Plate Pearls

This plate summarizes anatomical planes of study and terms of anatomical relationship. Note that in these images, the subject is always in a consistent anatomical position, with the head and toes directed anteriorly and the arms lateral to the trunk with the palms facing anteriorly.

The left image shows three key anatomical planes of study: frontal, or coronal; transverse, or horizontal; and sagittal.

• The frontal plane is drawn through the body longitudinally, dividing the body into anterior and posterior portions.

• The transverse plane is drawn horizontally through the body, dividing it into superior and inferior parts.

• The sagittal plane is drawn through the body longitudinally, dividing it into left and right sides.

In the right image, terms of orientation are provided for comparison purposes.

• Superior refers to structures that are closest to the top of the skull.

• Inferior refers to structures closest to the plantar surface of the foot.

• Cranial relates to the head.

• Caudal relates to the tail, or coccyx.

• Anterior refers to the front of the body.

• Posterior refers to the back of the body.

• Medial refers to structures that are closer to the midline of the body.

• Lateral refers to structures that are farther from the midline.

• Proximal refers to the point where a limb attaches to the trunk.

• Distal refers to a structure located farther from the point of attachment to the trunk.

When considering the surface anatomy of the head and neck during a physical examination, it is important to use appropriate and specific terminology for body regions and to look for symmetry between the left and right sides of the body.

This plate highlights the descriptive terms used for anterior body regions, divided into the head and neck, trunk, and limbs.

Note that the anterior aspect of the head is organized into the forehead and face.

• The forehead is termed the frontal region because it overlies the frontal bone.

• The face includes the eye, nose, cheek, mouth, and chin.

  • The orbital region surrounds the eyes, and the nasal region surrounds the nose. The oral region surrounds the mouth, and the cheek overlies the zygomatic bone of the facial skeleton. The mental region refers to the chin.

The neck is a transitional region between the head, thorax, and upper limb.

The trunk is formed by the thorax, abdomen, and perineum. Note the breast as a key surface anatomical feature in the thorax.

The upper limbs are organized from proximal to distal into the shoulder, axilla, arm, forearm, wrist, and hand.

• The cubital region lies anterior to the elbow and is a transitional area between the arm and the forearm.

• The anterior, or palmar, surface of the hand is visible in this image.

The lower limbs are organized from proximal to distal into the hip, thigh, leg, and foot.

• The hips serve as transitional sites between the trunk and lower limbs.

• The knee is the transitional region between the thigh, or femoral region, and the leg.

• The ankle is the transitional region between the leg and the dorsum of the foot.

This plate highlights the descriptive terms used for posterior body regions, divided into the head and neck, back, and limbs.

From a posterior view of the head, the temples (or temporal fossae), occiput (back of the head, or squamous part of the occipital bone), and ears are visible.

From a posterior view, the neck appears as a transitional region between the head and back.

In addition, the back transitions laterally into the upper limbs. From proximal to distal, identify the shoulder, axilla (armpit), arm (brachium), forearm (antebrachium), and dorsum, or back of the hand. The elbow transitions from the arm to the forearm, and the wrist adjoins the forearm and the hand.

• The back transitions to the lower limb at the hip. Note the continuity of the gluteal region with the thigh. The popliteal fossa is located posterior to the knee and represents a transitional region between the thigh and the leg. The leg transitions to the foot at the ankle.

This plate highlights the anatomical and functional organization of the nervous system.

Anatomically, the nervous system is organized into a central nervous system (CNS), which consists of the brain and spinal cord, and the peripheral nervous system, which consists of cranial and spinal nerves.

In the peripheral nervous system, receptors monitor either the outside world and body position ( somatic sensory receptors) or the internal body conditions and organ systems ( visceral sensory receptors). These sensory receptors make up the afferent division of the nervous system, which brings information into the central nervous system for processing.

The central nervous system then initiates a motor response to the sensory input through its efferent division. The efferent nervous system can be divided into a somatic motor and an autonomic motor system.

• The somatic nervous system innervates skeletal muscles of the body.

• The autonomic nervous system innervates smooth muscle, cardiac muscle, and glands. The autonomic nervous system can be further subdivided into sympathetic and parasympathetic divisions, which exert antagonistic effects on smooth muscle, cardiac muscle, and glands.

The activity of the gut is regulated by the autonomic nervous system. The gut also has an extensive neural plexus, however, which allows it to function independent of the autonomic system. This is why the gut is often classified as a separate component of the autonomic nervous system.

This plate demonstrates the anatomical distribution of the dermatomes, which are strips of skin innervated segmentally by cutaneous branches from one predominant spinal cord level. Dermatomes are clinically useful in diagnosing radiculopathies.

Note that there is no C1 dermatome because the C1 spinal nerve lacks somatic sensory fibers; instead, it provides motor innervation to the suboccipital muscles in the posterior neck and the skeletal muscles related to the hyoid bone in the anterior neck.

Dermatomes C2‒4 supply the posterior scalp and both the anterior and posterior aspects of the neck.

Dermatomes C5‒T1 are dedicated to the sensory innervation of the upper limb, with C6 supplying the skin over the thumb and T1 innervating the skin of the fifth digit (the pinky finger).

Dermatomes T2‒T12 provide segmental sensory innervation to the thoracoabdominal wall, with T10 lying at the level of the umbilicus.

Lumbar and sacral dermatomes supply the skin of the lower limb, with the L1 dermatome located anteriorly at the groin region and posteriorly in the superior gluteal region. In general, the embryonic rotation of the lower limbs positions the lumbar dermatomes more anteriorly and the sacral dermatomes more posteriorly.

The sympathetic nervous system is a division of the autonomic nervous system and is responsible for the “fight or flight” response. The targets for the sympathetic nervous system are smooth muscle, cardiac muscle, and glands.

• The sympathetic nervous system consists of a two-neuron chain extending from the spinal cord to the target organ, including a preganglionic and a postganglionic neuron. These two neurons communicate at an autonomic ganglion, which serves as the reference point for their naming scheme.

• The two main types of sympathetic autonomic ganglia are paravertebral (or sympathetic chain/trunk) and prevertebral.

All preganglionic sympathetic neurons have their cell bodies in the spinal cord, between T1 and L2 levels; this is the basis for designating the sympathetic system as a thoracolumbar system. These preganglionic neurons send their axons into the sympathetic chain, located just to the right of the spinal cord in this plate. In the sympathetic chain ganglion, a synapse will occur if the target is smooth muscle or a gland in the head, limbs, or body wall, or if the target is a thoracic organ.

• If the target is smooth muscle or a gland in the abdomen or upper pelvis, the synapse will occur in a prevertebral ganglion, such as the celiac, aorticorenal, superior, or inferior mesenteric ganglia.

For organs such as the rectum, prostate, or urinary bladder, sympathetic synapses occur in unnamed sympathetic ganglia in an autonomic plexus in the pelvis, termed the inferior hypogastric plexus.

The parasympathetic nervous system is a division of the autonomic nervous system and is responsible for the “rest and digest” response. The targets for the parasympathetic nervous system are smooth muscle, cardiac muscle, and glands.

• The parasympathetic nervous system consists of a two-neuron chain extending from the brain stem and spinal cord to the target organ, including a preganglionic and a postganglionic neuron. These two neurons communicate at an autonomic ganglion, which serves as the reference point for their naming scheme.

• The two main types of parasympathetic autonomic ganglia are cranial ganglia (ciliary, otic pterygopalatine, submandibular, or COPS ganglia) and intramural ganglia within the wall of the target organ.

Preganglionic parasympathetic neurons have their cell bodies in the brain stem or the sacral spinal cord (S2‒4); this is the basis for designating the parasympathetic system as a craniosacral system.

Parasympathetic fibers arising in the brain stem travel to their target organs via specific cranial nerves (CNs), including CN III (oculomotor), VII (facial), IX (glossopharyngeal), and X (vagus). CNs III, VII, and IX use cranial parasympathetic ganglia for their synapses (CN III uses ciliary ganglion, CN VII uses both pterygopalatine and submandibular ganglia, CN IX uses otic ganglion). CN X provides parasympathetic innervation to the thorax and abdomen as far distal as the mid–transverse colon; its preganglionic fibers synapse in intramural ganglia in the wall of the target organ.

Parasympathetic fibers arising in the sacral spinal cord travel via ventral rami of spinal nerves, which give rise to pelvic splanchnic nerves, which synapse in intramural ganglia in the wall of the target organ.

This plate summarizes the skeletal system of the body, which is formed by an axial skeleton and an appendicular skeleton.

The axial skeleton forms the main axis of the body and consists of 80 bones that form the skull, vertebral column, and thoracic cage.

• The skull includes the neurocranium, which includes the frontal, sphenoidal, ethmoidal, parietal, temporal, and occipital bones. The viscerocranium includes the nasal, lacrimal, maxillary, palatine, vomer, and inferior nasal conchae bones. Other associated bones of the skull include the middle ear ossicles, the mandible (jawbone), and the hyoid bone.

• The vertebral column includes 7 cervical, 12 thoracic, and 5 lumbar vertebrae, along with the sacrum and coccyx. The thoracic cage includes 12 pairs of ribs and a sternum.

The appendicular skeleton is formed by the skeleton of the upper and lower limbs.

• Each upper limb is supported by the pectoral girdle, which attaches the upper limb to the trunk, along with the free part of the upper limb.

  • The pectoral girdle is formed by the clavicle and scapula, and the free part of the upper limb includes the humerus, radius, ulna, carpal bones, metacarpal bones, and phalanges.

• Each lower limb is supported by the pelvic girdle, which attaches the lower limb to the trunk, along with the free part of the lower limb.

  • The pelvic girdle consists of the hip bones, and the free part of the lower limb includes the femur, patella, tibia, fibula, tarsal bones, metatarsal bones, and phalanges.

This plate outlines the key features of the synovial joint, the most common and most movable type of joint in the human body. The upper figure in this plate demonstrates a coronal section through two standard synovial joints.

Synovial joints are supported externally by a fibrous articular capsule that is continuous with the periosteum of the articulating bones. The articulating bones of a joint consist of a shaft, or metaphysis, and an end, or epiphysis. The epiphyses in the synovial joints are covered by a layer of hyaline cartilage, known as articular cartilage, which serves to absorb shock and reduce friction during movement. The inner surface of the articular cartilage and articular capsule in a synovial joint is lined by a synovial membrane that produces a lubricant known as synovial fluid.

Part A shows a hinge type of synovial joint, as is observed in the elbow joint. Hinge joints allow motion primarily in one plane and work much like the hinge of a door, where one bone moves while the other remains stationary. Most hinge joints allow flexion and extension in one plane, with only small degrees of motion in other planes.

Part B demonstrates a pivot type of synovial joint, as is observed in the atlantoaxial joint between vertebrae C1 and C2 in the neck. Pivot joints permit axial rotation, where the mobile bone rotates within a ring formed by the surface of a second bone. The atlantoaxial joint allows the head to turn to look left and right and to shake the head “no.”

Part C shows a saddle type of synovial joint, as is observed in the carpometacarpal joint of the thumb. The articulating surfaces both have concave and convex surfaces, which allow them to interface like two opposing saddles. Saddle joints allow movement in two directions, that is, they allow flexion, extension, abduction, and adduction.

Part D shows a condyloid synovial joint, which is formed by the oval-shaped end of one bone fitting into a similarly oval hollow of another bone. The knee is one example of this type of joint, which is similar to the saddle joint but allows less movement.

Part E shows a ball-and-socket joint, such as the hip joint, which consists of a rounded ball-like end of one bone (femoral head) fitting into a cup-like socket of another bone (acetabulum). This arrangement allows for the greatest range of motion, with movement in all directions possible.

Planar joints such as the acromioclavicular joint allow for gliding movements, which have a limited range of motion with no rotation.

This plate organizes the skeletal muscles of the body regionally.

In the left image, the anterior muscle groups are shown, including the muscles of facial expression and the neck muscles superior to the clavicle. Inferior to the clavicle, note the pectoral, anterior abdominal wall, and perineal musculature. In the upper limbs, the muscle groups are organized as shoulder, anterior arm, anterior forearm, and hand muscles. In the lower limbs, the muscle groups are organized as anterior thigh, medial thigh, anterior leg, and lateral leg and foot muscles.

The image on the right shows the posterior muscle groups, including the superficial back muscles. These blend with the shoulder muscles, which in turn are continuous with the muscles of the posterior arm and posterior forearm. The lower aspect of the posterior trunk is characterized by the superficial gluteal muscles, which blend inferiorly with the posterior thigh and posterior leg musculature.

A myotome is a group of skeletal muscles innervated by a single spinal nerve. The muscle movement of each myotome is controlled by motor nerves from the same motor section of a spinal nerve root. Knowledge of myotomes is important for testing spinal nerve compression. Most muscles in the limbs are innervated by more than one spinal nerve and therefore have multiple myotomes.

When considering the segmental motor innervation to the upper limb, note that the more proximal muscles are controlled by upper spinal nerve root levels and the more distal muscles in the hand are regulated by lower spinal nerve root levels.

Segmental motor innervation in the upper limb is controlled by spinal nerves C5‒T1. Flexion and extension of the arm at the shoulder are guided by C5 and C6, respectively. Forearm flexion is controlled by the C5 and C6 spinal nerve levels (a mnemonic is “five, six, pick up sticks”), from which the stimulation travels through peripheral nerves such as the musculocutaneous nerve. Forearm extension is mediated by the C6‒C8 spinal levels, from which the stimulation travels through the radial nerve. At the wrist, flexion is controlled by C7‒T1, and extension is elicited by stimulation of C7‒C8. Supination of the forearm is controlled by C5‒C7, and pronation is regulated by C6‒C8. Finally, flexion and extension of the digits of the hand are activated by different motor fibers of C7‒T1.

Segmental motor innervation of the lower limb is regulated by spinal nerves L1‒S2. Adduction of the thigh is governed by L2‒L4, and abduction of the thigh is controlled by L5‒S1. Medial rotation of the thigh is controlled by L4‒L5, whereas lateral rotation is governed by L5‒S1. Flexion of the thigh at the hip is regulated by L2‒L3, and extension of the thigh at the hip is controlled by L5‒S1. Flexion of the leg at the knee is regulated by L5‒S1, and extension of the leg at the knee is via L3‒L4. Subtalar inversion is mediated by L4‒L5 and eversion by L5‒S1. Dorsiflexion of the ankle is regulated by L4‒L5 and plantarflexion by S1‒S2.

The integument (skin) is considered the largest organ in the human body and serves as the major barrier between the internal anatomy of the body and the outside world.

The epidermis is the most superficial layer of the integument. It consists of five layers (strata), which can be considered developmental stages of the epidermis. Cells in the deepest layer of the epidermis, the stratum basale, mature and move up through the layers above, changing their appearance as they move from one layer to the next.

The stratum corneum is the outermost layer of the epidermis, and its keratin-dense composition is responsible for the protective function of the epidermis.

Deep to the stratum corneum lies the stratum lucidum, which consists of several layers of flattened dead cells that have not yet undergone desquamation to form the stratum corneum.

Deep to the stratum lucidum lies the stratum granulosum, which contains cells filled with keratohyalin granules. These granules contain lipids that are instrumental in providing a protective barrier against the outside world.

Deep to the stratum granulosum is the stratum spinosum. The cells in the stratum spinosum are anchored together by numerous desmosomes, and these connections look like little spines, or “prickles.”

Finally, the basal cell layer (stratum basale) consists of dividing cells that lie closest to the dermis.

The dermis underlies the epidermis and consists of the connective tissue layer of the skin. It contains the neurovasculature and sweat glands. The dermis is organized into a more superficial papillary layer and a deeper reticular layer. The papillary layer of the dermis forms little hills, or papillae, of loose connective tissue that extend up to the stratum basale of the epidermis. It is in the papillary layer that free nerve endings are found, along with tactile receptors known as Meissner’s corpuscles.

The reticular layer of the dermis lies deeper in the skin and is formed by dense irregular connective tissue. This layer conveys strength and elasticity to the skin. The reticular dermal layer contains hair follicles and pacinian (lamellar) corpuscles, along with sweat and sebaceous glands.

Hair follicles are specializations of the epidermis. At the base of a hair follicle, note the dermal papilla that contains the blood supply for the follicle. The matrix of the follicle contains proliferative cells that form the hair. Each hair is organized into a central medulla, surrounded by a cortex, and finally enclosed by a surface cuticle. Keratinized cells from the hair matrix form the internal root sheath. The external root sheath is formed as an invagination of the epidermis, and it surrounds the internal root sheath. The glassy membrane separates the external root sheath from the surrounding reticular dermal connective tissue.

Sebaceous glands are located in the reticular dermis and are closely associated with hair follicles. They release sebum onto the hair by the process of holocrine secretion.

Closely associated with the fibrous capsule surrounding the glassy membrane of the hair follicle is found the arrector pili muscle. It is a smooth muscular structure that elevates the hair to create goosebumps and also gently compresses the sebaceous glands to facilitate sebum release onto the hair.

The subcutaneous tissue, or hypodermis, lies deep to the reticular dermis. The hypodermis consists largely of adipose tissue, with retinacula cutis extending through it from the deep fascia of the underlying skeletal musculature. Sweat glands may extend into the hypodermis.

The cardiovascular system consists of the heart and blood vessels (including the arteries, arterioles, capillaries, venules, and veins), which work together to provide the blood supply to the body.

The heart is a dual pump organized into a right side, which transports deoxygenated blood from the body to the lungs, and a left side, which transports oxygenated blood to the body.

Venous blood from the body enters the right atrium (RA) of the heart through the superior and inferior venae cavae. From the right atrium, blood enters the right ventricle (RV) and then the pulmonary artery. The pulmonary artery delivers blood to the lungs for oxygenation.

Freshly oxygenated blood from the lungs is collected by pulmonary veins, which drain into the left atrium (LA) of the heart. From the left atrium, blood enters the left ventricle and then passes out to the aorta. The aorta branches into arteries that supply oxygen and nutrient-rich blood to the brain, the lungs themselves, the heart’s myocardium, the digestive tract (stomach), the musculoskeletal system, and the kidneys, as well as the skin and other organs.

The heart serves as the pump that propels blood into the great arteries of the heart, namely, the aorta and pulmonary artery. These large arteries serve as distribution blood vessels that carry blood away from the heart. As they do so they branch into progressively smaller blood vessels. Large arteries have muscular walls that are thick and elastic to accommodate blood flow at high pressures.

Smaller arteries have proportionately more smooth muscle in their walls, a type of muscle that can regulate the blood flow to specific regions of the body. Small arteries branch into even smaller blood vessels termed arterioles. When arterioles constrict, they increase resistance, causing a reduction in blood flow to their capillaries and therefore a large decrease in blood pressure. Arterioles regulate the pressure and flow within the cardiovascular system.

Arterioles give rise to capillaries, which are the smallest vessels in the circulatory system. Capillaries are the primary exchange blood vessels in the body, allowing for water, gases, electrolytes, proteins, and metabolites to move between the blood plasma and the extracellular space (interstitium).

Capillaries are drained by venules, which also serve as exchange blood vessels for large macromolecules and fluid. Venules join to form veins, which ultimately transport blood back to the heart. Veins serve as capacitance blood vessels, meaning that they are the sites where most of the blood volume is stored and where the regional blood volume is regulated.

This plate highlights the arterial system and the main pulse points of the body.

Blood from the left ventricle of the heart travels through the aorta to reach the rest of the body. From the aortic arch, note the right and left common carotid arteries, which produce the carotid artery pulse.

• Each common carotid artery gives rise to an internal and external carotid artery.

• The facial artery is a branch of the external carotid artery and provides a pulse over the inferior aspect of the mandible.

The subclavian artery branches from the aortic arch on the left and from the brachiocephalic trunk on the right. The subclavian artery becomes the axillary artery as it passes distal to the first rib.

• The axillary artery, in turn, becomes the brachial artery at the distal border of the teres major muscle. The brachial artery pulse may be palpated on the inner aspect of the midarm.

• The brachial artery divides in the cubital fossa into the radial and ulnar arteries, both of which produce a pulse that is palpable at the wrist. The radial and ulnar arteries form an arterial anastomosis in the hand, termed the palmar arches.

The aortic arch becomes the descending aorta distally, which gives rise to numerous segmental branches, including the renal arteries, as well as unpaired branches, including the celiac trunk and the superior and inferior mesenteric arteries. The descending aorta terminates distally as the common iliac arteries.

Each common iliac artery divides into an internal and an external iliac artery. The external iliac artery becomes the femoral artery as it travels inferior to the inguinal ligament.

• The femoral artery pulse may be palpated midway between the pubic symphysis and anterior superior iliac spine.

• The femoral artery gives rise to the deep femoral artery in the proximal thigh.

The femoral artery then continues distally to become the popliteal artery posterior to the knee.

• The popliteal artery pulse may be palpated posterior to the knee. The popliteal artery branches terminally to form the anterior and posterior tibial arteries.

• The anterior tibial artery becomes the dorsalis pedis artery as it crosses the ankle joint. This pulse is palpable lateral to the extensor hallucis longus tendon on the dorsum of the foot.

• The posterior tibial artery pulse is palpable posterior to the medial malleolus. The posterior tibial artery divides into medial and lateral plantar arteries in the foot.

The plantar arch is an arterial anastomosis between branches of the dorsalis pedis artery and the lateral plantar artery.

This plate highlights the systemic venous drainage of the body, including superficial and deep veins of the limbs.

Venous blood is returned to the heart via the superior and the inferior vena cava.

The azygos vein in the posterior mediastinum receives venous blood from the posterior thoracic wall and provides collateral circulation between the superior and the inferior vena cava.

The superior vena cava receives blood from the right and left brachiocephalic veins. The brachiocephalic veins are formed by the subclavian and internal jugular veins. Note the more superficial external jugular vein draining to the subclavian vein.

• The subclavian vein is continuous with the axillary vein at the lateral border of the first rib.

• The axillary vein is formed by the union of the brachial vein and the basilic vein.

  • The brachial vein is the deep vein of the arm and receives venous drainage from the radial and ulnar veins.

  • The cephalic and basilic veins are superficial veins of the upper limb.

The inferior vena cava receives blood from a variety of sources, including the renal veins and common iliac veins. Each common iliac vein receives blood from an internal and an external iliac vein. The external iliac vein is continuous with the femoral vein at the level of the inguinal ligament.

The femoral vein receives blood from the deep femoral vein and the superficial great saphenous vein. The femoral vein becomes the popliteal vein posterior to the knee.

The popliteal vein is formed by the union of the anterior and posterior tibial veins of the leg, which contribute to the dorsal venous arch of the foot.

The lymphatic system consists of several components, including lymphatic vessels, lymph nodes, and lymphatic organs.

Lymphatic organs highlighted in this image include the thymus gland, spleen, tonsils, and lymphoid nodules of the intestine.

• The thymus gland plays a key role in T lymphocyte development.

• The spleen recycles old red blood cells and combats certain types of bacterial infections.

• The tonsils are lymphoid organs that help protect the respiratory and gastrointestinal systems against infection.

• The lymphoid nodules in the intestine play an important role in monitoring and responding to pathogens in the gastrointestinal tract.

Lymph vessels are an integral part of the cardiovascular system, collecting excess extracellular fluid that is not resorbed at the capillary level. Lymph vessels periodically course through lymph nodes, which are lymphatic organs responsible for sampling and filtering the lymph before its drainage into the systemic venous system.

Lymph from the lower limbs, abdomen, and left side of the head, neck, upper limb, and thorax is drained into the thoracic duct. Lymph from the right upper limb, thorax, head, and neck drains to the right lymphatic duct. Each of these ducts empties into the venous angle, where the internal jugular vein joins the subclavian vein.

Lymph from the lower limbs drains through inguinal lymph nodes to iliac lymph nodes, to lumbar lymph nodes, and then to the cisterna chyli. The cisterna chyli narrows superiorly to become the thoracic duct.

Lymph from the upper limbs and breast drains primarily to the axillary lymph nodes, which then drain either to the thoracic duct on the left or to the right lymphatic duct.

The respiratory system functions in ventilation, or the movement of air between the atmosphere and the lungs by the processes of inspiration and expiration. Anatomically, the respiratory system consists of an upper respiratory tract that is located superior to the thorax and a lower respiratory tract that lies within the chest. The upper respiratory tract includes the nasal cavity, pharynx, and larynx, and the lower respiratory tract consists of the trachea, bronchi, and lungs. In this plate, the upper respiratory system is demonstrated in sagittal section and the lower respiratory system is intact.

Inspiration occurs through either the nasal cavity or the oral cavity. The nasal cavity is designed to warm and humidify the air as it enters the body. The surface area across which air is warmed and humidified is increased by the presence of scroll-shaped bones, known as conchae, projecting from the lateral walls of the nasal cavities.

From the nasal cavity, air enters the pharynx, a musculofascial tube extending from the skull base into the neck. It is organized into three regions. The upper pharynx, or nasopharynx, receives air from the nasal cavity. The nasopharynx is continuous inferiorly with the oropharynx. Air entering the body through the oral cavity passes directly into the oropharynx. From the oropharynx, air moves into the laryngopharynx, or hypopharynx, from which it enters the larynx, or voice box.

The larynx contains the vocal folds, which abduct and adduct to regulate the passage of air into and out of the lower respiratory tract.

From the larynx, air enters the trachea, which bifurcates into left and right main bronchi that convey air to the left and right lungs, respectively. Note that the main bronchi enter the lung at the hilum, which is a region on the medial aspect of each lung where structures, including the bronchi and neurovasculature, enter and exit the lung.

The anatomical structure with which each lung maintains inflation is the pleura. Pleural membranes are serous membranes that cover the lung itself, as well as all surfaces in contact with the lungs in the thorax. Visceral pleurae cover each lung and then reflect off of the lung at the hilum to form the parietal pleura, which lines the walls of the pleural cavity. The parietal pleura is subdivided into the costal pleura, diaphragmatic pleura, mediastinal pleura, and cervical pleura. The visceral and parietal pleurae slide over one another, with only a few drops of serous fluid located in the pleural cavity between them. If air, blood, or a fluid enters the pleural cavity and separates the visceral and parietal layers of pleura, a collapsed lung will result.

The digestive system consists of the tubular gastrointestinal (GI) tract and the accessory digestive organs, including the salivary glands, liver, gallbladder, and pancreas. Digestion begins in the oral cavity, as the teeth and tongue facilitate the mechanical breakdown of food. Salivary glands, including the sublingual, submandibular, and parotid glands, secrete saliva to initiate digestion. These glands are named by their anatomical location, with the sublingual salivary gland lying inferior to the tongue in the floor of the mouth, the submandibular salivary gland located inferior to the mandible, and the parotid salivary gland situated adjacent to the ear, or otic region.

From the oral cavity, a bolus of food moves posteriorly into the pharynx, a musculofascial tube. The skeletal muscles of the pharynx propel the bolus of food inferiorly into the esophagus.

The esophagus transports food into the stomach. It is a transitional region from the more somatic oral cavity and pharynx to the more visceral segment of the digestive tract.

From the esophagus, the bolus of food enters the stomach. Here, the chemical breakdown of food occurs by the actions of acids and enzymes and the mechanical breakdown continues via muscular contractions. In addition, some amount of water, alcohol, and minerals is absorbed from the stomach into the bloodstream.

From the stomach, the semidigested food, or chyme, enters the small intestine. The small intestine is the site into which accessory digestive glands such as the liver, gallbladder, and pancreas release their products.

The liver is the site of bile secretion, which is important for lipid digestion. The gallbladder functions in the concentration and storage of bile. The liver is also where nutrients are stored and cellular fuels are produced. In addition, the liver produces plasma proteins and clotting factors and is a site for detoxification and phagocytosis.

The pancreas exhibits both exocrine and endocrine functions. Its exocrine structures secrete buffers and digestive enzymes, and its endocrine components secrete hormones to regulate digestion.

The small intestine is the site where acid neutralization occurs, along with the absorption of water, nutrients, vitamins, and ions. It is also a site for the immune host defense.

Finally, the large intestine serves to dehydrate and compact any remaining indigestible material from the small intestine. The large intestine further serves to resorb water and electrolytes. Like the small intestine, it is a site for the immune host defense.

The urinary system serves a variety of functions in the human body, including the elimination of waste from the body, the regulation of the blood volume, blood pressure, and electrolyte and metabolite levels, and the mediation of the blood pH.

The urinary system includes the kidneys, ureters, urinary bladder, and urethra. The kidneys produce urine, which is conveyed by the ureters to the urinary bladder. The kidneys are abdominal organs, lying in a retroperitoneal position at vertebral levels T12‒L3. The ureters are muscular ducts that exit the hilum of each kidney, descend along the posterior abdominal wall, and pass over the pelvic brim to enter the pelvis. In the pelvis, the ureters open into the fundus of the urinary bladder.

Anatomically, the suprarenal glands are included in the urinary system due to their position superior to the kidneys. The suprarenal glands have an endocrine function.

The reproductive system consists of the internal and external organs involved in sexual reproduction. The ovaries and the testes are the gonads, or principal sex organs, which produce oocytes (eggs) and sperm, respectively.

In females, the internal genital organs include the ovaries, uterine tubes, uterus, and vagina; the mammary glands are external, accessory reproductive glands. At puberty, ovulation produces one or more oocytes from the ovary, which are collected by the uterine tube. If sexual intercourse occurs during ovulation, sperm are deposited into the vagina and travel through the uterus and into the uterine tube, where fertilization may occur. Should fertilization occur, the zygote (or fertilized egg) will then migrate to the uterus for implantation and development. Mammary glands in the breast function as accessory glands of reproduction in females. They are modified sweat glands that have the capacity to secrete milk under appropriate hormonal stimulation following childbirth. The breasts are located in the anterior thoracic wall and consist of mammary glandular tissue, along with adipose and fibrous tissue.

In males, the internal genital organs include the testes, epididymides, ductus deferens, seminal glands, and prostate. The penis is the external genital organ in the male. Sperm are produced by the testes and stored in the epididymides. Sperm are transported via the ductus deferens to be released into the male urethra during ejaculation. In addition to sperm, seminal fluid contains secretions from seminal glands and the prostate. The seminal glands produce a fructose-rich secretion to nourish sperm that mixes with sperm as they enter the urethra. The prostate secretes a thin milky fluid that is critical in activating sperm.

The endocrine system consists of a variety of ductless glands that secrete hormones into the bloodstream to act on different organs in the body to maintain homeostasis and regulate reproduction and development.

The pituitary gland is often termed the master gland of the body because it regulates the function of many other endocrine organs. The pituitary gland is organized into an anterior lobe and a posterior lobe, each of which produces discrete hormones.

The anterior lobe of the pituitary releases ACTH (adrenocorticotropic hormone, which regulates the suprarenal glands), TSH (thyroid-stimulating hormone, which regulates the thyroid gland), GH (growth hormone), PRL (prolactin to stimulate milk production in the female breast), FSH (follicle-stimulating hormone, which regulates the ovaries and testes), LH (luteinizing hormone, which regulates the ovaries and testes), and MSH (melanocyte-stimulating hormone, which produces pigmentation and preserves the skin from ultraviolet rays and controls the appetite).

The posterior lobe of the pituitary secretes oxytocin (which stimulates milk flow in breastfeeding women and helps labor to progress in pregnant females) and vasopressin (ADH, or antidiuretic hormone, which regulates the water balance in the body and the sodium levels in the blood).

The hypothalamus controls pituitary hormones through its release of TRH (thyrotropin-releasing hormone), CRH (corticotropin-releasing hormone), GHRH (growth hormone‒releasing hormone), GnRH (gonadotropin-releasing hormone), and somatostatin. These hypothalamic hormones collectively regulate the body temperature, appetite and weight, mood, sex drive, sleep, and thirst.

The pineal gland produces melatonin, which helps to maintain circadian rhythms and regulates reproductive hormones (e.g., it can block the secretion of gonadotropins from the anterior pituitary gland). It was once termed the third eye due to its position deep within the brain and its connection to light processing within the central nervous system. Pineal literally translates to “pine cone‒shaped,” thus describing its appearance.

The thyroid gland secretes thyroxine (T4), triiodothyronine (T3), and calcitonin, which produce a variety of effects on the metabolism. Calcitonin reduces the calcium levels in the blood. The release of T3 and T4 is regulated by a negative feedback loop with the hypothalamus and anterior pituitary gland.

Parathyroid glands produce parathyroid hormone (PTH) in response to low blood calcium levels.

The thymus produces thymopoietin, which regulates immune function and T-cell differentiation.

The heart produces atrial natriuretic peptide (ANP), which functions to lower the blood pressure and control the electrolyte homeostasis.

The digestive tract produces enteroendocrine hormones such as gastrin, secretin, cholecystokinin (CCK), gastric inhibitory peptide (GIP), and motilin. Gastrin is responsible for gastric motility and the secretion of hydrochloric acid into the stomach. Secretin is produced by the duodenum and is responsible for the regulation of gastric acidity and pancreatic bicarbonate and osmoregulation. CCK regulates pancreatic enzyme secretion and gastric motility and also serves as a satiety signal. GIP is produced by the small intestine, and it increases insulin levels. Motilin is produced in the small intestine to stimulate gastric and small intestinal motility, causing undigested food to move toward the colon.

Pancreatic islets secrete insulin, glucagon, and somatostatin. Somatostatin inhibits insulin and glucagon release.

Suprarenal glands have an inner medulla, which produces epinephrine and norepinephrine, and an outer cortex, which secretes mineralocorticoids, glucocorticoids, and androgens.

Kidneys produce erythropoietin (EPO), calcitriol, and renin. Erythropoietin plays an important role in the production of red blood cells. Calcitriol is the active form of vitamin D and regulates the amount of calcium in the body. Renin increases the blood pressure.

Adipose tissue produces leptin, which helps to regulate the body weight. Leptos translates to “thin.” Leptin is sometimes referred to as the fat controller.

Ovaries produce estrogens, progestins, inhibin, and relaxin. Estrogen and progestins are necessary to prepare the uterus for menstruation, and their release is triggered by the hypothalamus. Inhibin signals the pituitary to inhibit FSH. Relaxin relaxes ligaments in the pelvis and softens and widens the cervix.

Testes produce androgens and inhibin. Testosterone is the hormone responsible for secondary sexual characteristics in the male, and it stimulates spermatogenesis. Sertoli cells produce inhibin, which is released into the blood when the sperm count is too high; this inhibits the release of GnRH and FSH, which slows spermatogenesis.

When considering the surface anatomy of the head and neck during a physical examination, it is important to look for symmetry between the left and right sides of the face and neck. The upper figure in this plate demonstrates key surface anatomical landmarks often used in physical examination.

The forehead is formed by the smooth convexity of the frontal bone. The supraorbital notch (or foramen) is located on the inferior edge of the frontal bone where it forms the upper border of the orbit (supraorbital margin). Just superior to the upper border of the orbit, a ridge known as the superciliary arch is observed; this arch lies deep to the eyebrows. The glabella is the smooth prominence superior to the nasal bones and between the superciliary arches. The infraorbital margin forms the lower border of each orbit and is formed by the zygomatic bone and the maxilla. The zygomatic bones extend laterally to form the prominence of the cheeks.

The external nose projects from the facial skeleton, with the nasal bones forming the bridge of the nose. The alae or wings of the nose surround the anterior nares or nostrils.

Just inferior to the nose is the philtrum, or the central depression between the nose and the upper lip. The inferior margin of the philtrum forms the downward arch of the “cupid’s bow” while the underlying fullness is the tubercle of the upper lip.

The external ear is a prominent feature of the lateral aspect of the head. The upper border of the ear is formed by the helix, while the antihelix is the Y shaped ridge just inferior to the helix. The tragus lies inferior to the helix and antihelix, located anterior to the external auditory meatus. The antitragus lies just posterior to the tragus, separated from it by the intertragic notch. Immediately inferior to the antitragus is the fleshy lobule.

The lower jaw is formed by the mandible, which is a U-shaped bone. The mental protuberance forms the midline prominence of the chin. The angle of the mandible is located more laterally, at the junction of the vertical ramus and horizontal body of the mandible.

The submandibular salivary gland can be palpated just under the inferior border of the mandibular body and should be soft and mobile and should not be tender to palpation. It should not be confused with an enlarged submandibular lymph node.

The thyroid cartilage is a key landmark for identifying the thyroid gland, which lies just inferior to it. The thyroid gland should be evaluated for asymmetry, nodules, or masses.

The sternocleidomastoid muscle is a key anatomical landmark in the neck, extending from the mastoid process of the temporal bone to the manubrium of the sternum (sternal head) and to the medial third of the clavicle (clavicular head). Its function is tested clinically by asking the patient to turn the head to the contralateral side against resistance.

The sternocleidomastoid delineates the anterior and posterior cervical triangles.

• The anterior triangle is formed by the anterior border of the sternocleidomastoid, midline of the neck, and inferior border of the body of the mandible. The apex of the anterior triangle is positioned at the jugular notch located at the superior end of the manubrium.

• The posterior triangle is formed by the posterior border of the sternocleidomastoid, anterior margin of the trapezius muscle, and the clavicle. In the posterior triangle, structures such as the inferior belly of the omohyoid muscle and the brachial plexus may be visible.

The external jugular vein is visible crossing the surface of the sternocleidomastoid. Typically, the vein is only visible immediately superior to the clavicle, although it may become distended if central venous pressure is elevated, as in heart failure or obstruction of the superior vena cava.

The lower illustration in this plate shows the key regions in the face and neck. The parietal region overlies the parietal bones on the superior aspect of the skull. The frontal region overlies the forehead. The orbital regions correspond to the eye sockets, or bony orbits. The nasal region includes the region where the external nose projects from the facial skeleton. Just lateral to the nasal region, note the infraorbital regions, just inferior to the orbits. Just lateral to the infraorbital regions, identify the zygomatic regions, overlying the zygomatic bone on each side. Lateral to the zygomatic region, note the auricular region, including the external ear.

• Inferior to the nasal region, note the oral region around the lips and labial commissures. Just lateral to the oral region is the buccal region. Even further laterally is the parotideomasseteric region, which includes the parotid glands and masseter muscles.

• Over the prominence of the chin, identify the mental region, which contains the mental protuberance.

• The neck is organized into anterior and posterior triangles by the sternocleidomastoid region. The anterior triangle includes the submandibular, submental, carotid, and muscular regions. Lateral to the sternocleidomastoid region, note the omoclavicular and occipital triangles forming the lateral region of the neck, as well as the posterior triangle or region of the neck.

When considering the sensory innervation pattern of the head and neck, it is important to remember that both cranial and spinal nerves supply different regions in this area.

The face is innervated by cranial nerve (CN) V, the trigeminal nerve. CN V has three divisions that innervate discrete regions of the face: ophthalmic (V ₁ ), maxillary (V ₂ ), and mandibular (V ₃ ).

• The ophthalmic division of the trigeminal nerve, V ₁ , is a purely sensory nerve that supplies the superior scalp, forehead, upper eyelid, and external nose. It has frontal, lacrimal, and infratrochlear branches.

  • The frontal nerve gives rise to the supraorbital and supratrochlear nerves that innervate the skin of the forehead.

  • The lacrimal nerve gives rise to a palpebral branch that supplies skin over the lateral upper eyelid.

  • The infratrochlear nerve is the terminal branch of the nasociliary branch of V ₁ and supplies the skin of the medial eyelid and the side of the nose above the medial canthus.

  • The external nasal nerve is the terminal branch of the anterior ethmoidal nerve, which in turn branches from the nasociliary nerve.

• The maxillary division of the trigeminal nerve, V ₂ , is also a purely sensory nerve that supplies the skin of the anterior temporal region, as well as the skin of the cheek, ala of the external nose, and the upper lip.

  • The zygomatic branch of V ₂ gives rise to two superficial nerves on the face, the zygomaticofacial and zygomaticotemporal nerves, which supply the lateral cheek and anterior temporal region, respectively.

  • The infraorbital nerve represents the continuation of V ₂ and innerves the skin of the cheek, lateral nose, and upper lip.

• The mandibular division of the trigeminal nerve, V ₃ , is a mixed nerve, with sensory and motor branches. The branches seen represent its superficial sensory nerves.

  • The auriculotemporal nerve supplies skin anterior to the external ear and posterior temporal region.

  • The (long) buccal nerve innervates the skin of the cheek over the buccal fat pad.

  • The mental nerve is the continuation of the inferior alveolar nerve, and it supplies the skin over the chin and lower lip.

The skin covering the posterior aspect of the head and neck is supplied segmentally by posterior rami of cervical spinal nerves 2 through 7. One named posterior ramus, the greater occipital nerve, is a branch of spinal nerve C2 and supplies the occipital region of the scalp.

The skin of the anterior and lateral neck is supplied by sensory branches of the cervical plexus, derived from the anterior rami of spinal nerves C2 to C4. These branches include the great auricular, transverse cervical, supraclavicular, and lesser occipital nerves.

• The great auricular nerve also supplies the skin over the angle of the mandible.

The face receives its arterial blood supply from direct or indirect branches of the external carotid and internal carotid arteries (see small figure at the lower left for a summary of the distribution of each artery).

• The external carotid artery gives rise to the facial artery, which courses obliquely and medially across the face from its point of origin and becomes the angular artery distal to the ala of the external nose.

• The external carotid artery gives rise to the posterior auricular artery, which supplies the scalp behind the external ear, and the occipital artery, which supplies the posterior scalp to the vertex (superior point of calvaria).

• The two terminal branches of the external carotid artery are the superficial temporal and maxillary arteries.

  • The superficial temporal artery gives rise to frontal, parietal, and transverse facial branches supplying the lateral face and scalp.

  • The maxillary artery gives rise to multiple branches coursing through the infratemporal and pterygopalatine fossae. One branch is the inferior alveolar artery, which supplies the mandible and mandibular teeth and gives off the mental artery, which exits the mandible anteriorly onto the face and supplies the skin of the chin (not labeled).

• The forehead is supplied by the supraorbital and supratrochlear arteries, derived from the ophthalmic artery, which is the first branch of the internal carotid artery.

The face and scalp are drained by superficial veins associated with either the external or the internal jugular vein.

• In terms of venous drainage from the face, the facial vein is responsible for superficial drainage. It courses obliquely and laterally across the face from its point of origin at the angular vein ; the name change occurs at the ala of the nose, as it does for its arterial counterpart. The facial vein receives blood from the infratemporal fossa by way of the deep facial vein, which drains the pterygoid venous plexus.

• The retromandibular vein drains most of the blood from the deep face and is formed by the junction of the superficial temporal and maxillary veins. The retromandibular vein divides into anterior and posterior divisions as it emerges inferiorly from the parotid gland.

  • The anterior division joins the facial vein to form the common facial vein, which drains into the internal jugular vein located deep to the sternocleidomastoid muscle.

  • The posterior division joins the posterior auricular vein to form the external jugular vein, located superficial to the sternocleidomastoid.

• The forehead is drained by the supraorbital and supratrochlear veins, which join the angular vein at the medial corner of the eye. The lateral scalp is drained by the superficial temporal vein, and the posterior scalp is drained by the posterior auricular vein. The posterior auricular vein receives blood from the mastoid emissary vein, which connects to the sigmoid dural venous sinus.

• The facial skeleton comprises the frontal and zygomatic bones and the bones of the nasal and orbital regions, the maxillae and mandible.

• Note the exit points for several branches of the trigeminal nerve onto the face, including the supraorbital foramina, or notches, in the frontal bone (for supraorbital nerve of CN V ₁ ), infraorbital foramina in the maxillae (for infraorbital nerve of CN V ₂ ), and mental foramina in the mandible (for mental nerve of CN V ₃ ).

• These three sets of foramina are aligned along a vertical axis on each side of the face, making them easy to identify.

The orbits are complex composite structures formed by multiple bony elements.

• Superficially, the frontal and zygomatic bones and the maxilla form the orbital margin.

• Extending posteriorly from the orbital margin, the orbit is a bony cavity configured as a pyramid. The apex of this pyramid is located at the optic canal housed in the lesser wing of the sphenoid. The optic canal conveys cranial nerve (CN) II, the optic nerve.

• The roof of each orbit is formed by the orbital plate of the frontal bone; the floor is formed by the maxilla and the zygomatic and palatine bones. The inferior orbital fissure separates the floor from the lateral wall and transmits the infraorbital nerve of CN V ₂ .

• Medially, the orbit is delimited by the orbital plate of the ethmoid, along with smaller contributions from the lacrimal bone, maxilla, and sphenoid. Foramina in the medial wall of each orbit transmit anterior and posterior ethmoidal nerves of CN V ₁ to the ethmoid air cells located medial to each orbit. The lacrimal bone contains a depression, or fossa, for the lacrimal sac that drains tears from the lacrimal gland into the nasolacrimal duct.

• Laterally, the zygomatic bone and the greater wing of the sphenoid form a strong buttress to guard against damage from trauma.

The nasal region is bounded superiorly by the paired nasal bones. The piriform aperture is a pear-shaped opening inferior to the nasal bones. The midline nasal septum can be observed by looking through the piriform aperture along with the nasal conchae on each lateral nasal wall.

In the upper radiograph, the posteroanterior (PA) view of the skull allows visualization of superficial and deep landmarks concurrently.

• Note the superior position of the sagittal suture separating the parietal bones, along with the posteriorly located lambdoid suture, which delineates the parietal from the occipital bones.

• Note the position of the orbits and the deeper structures that are visible relative to them, including the lesser wing of the sphenoid bone and the petrous part of temporal bone.

• The foramen rotundum, clearly visible in this view, conveys the maxillary division of the trigeminal nerve.

• The nasal septum divides the nasal cavity into right and left sides, with nasal conchae projecting from the lateral nasal wall on each side.

• Note that pneumatized bones, such as the maxilla with its maxillary sinus, appear radiolucent, or darker, than surrounding areas of the skull. The frontal sinus and mastoid cells also demonstrate this feature in this image.

• In the upper neck, note the atlas (C1) and axis (C2).

• The body, angle, and ramus of the mandible, or lower jaw, are also visible.

The lower radiograph is an occipitomental (OM), or Waters’, view of the skull, which is angled with the patient looking superiorly. This approach is useful in evaluating facial fractures and acute sinusitis.

• Note the frontal sinuses extending superior to the supraorbital margin.

  • On the lateral aspect of the orbit, the zygomaticofrontal suture is where the zygomatic and frontal bones articulate.

  • On the medial aspect of the orbit, note the ethmoidal sinus.

  • At the inferior margin of the orbit, note the infraorbital foramen and maxillary sinus.

• The nasal septum is readily identifiable here, separating the left and right nasal cavities.

• On the lateral aspect of the facial skeleton, note the zygomatic arch and mandibular condyle.

• Inferiorly, the angle of the mandible is visible, along with the lateral mass of C1 and the dens of C2.

The lateral view of the skull is characterized by features of both the facial skeleton (viscerocranium) and the brain case (neurocranium).

On each side of the neurocranium, a readily visible depression termed the temporal fossa houses the temporalis muscle.

• The temporal fossa is formed by four bones: frontal, parietal, sphenoid, and temporal; the pterion is a sutural junction formed where these bones meet.

• At the superior edge of each fossa are two temporal lines. The superior line serves as the attachment for the temporal fascia overlying the temporalis muscle. The inferior line serves as the upper attachment for the temporalis muscle itself.

• The temporal fossa is in open communication with the more inferior infratemporal fossa, whose superior boundary is the infratemporal crest, visible on the lower image. The tendon of the temporalis muscle courses inferiorly, deep to the zygomatic arch, to attach on the coronoid process of the mandible and to the anterior border of the mandibular ramus, almost to the third molar tooth.

The external acoustic meatus is also visible on this lateral view of the neurocranium. This opening funnels sound waves to the tympanic membrane at the lateral end of the meatus (not visible on this image).

The mastoid process is located just posterior to the external acoustic meatus and serves as an attachment for the sternocleidomastoid muscle in the neck.

On each side of the viscerocranium, inferior to the temporal fossa, the superficial anatomy of the mandible can be studied. The mandible has two processes, a more anterior coronoid process, to which the temporalis tendon attaches, and a more posterior condylar process that contributes to the temporomandibular joint. These two processes join inferiorly to form the ramus of the mandible, to which masseter and medial pterygoid attach.

On each side of the viscerocranium, inferior to the temporal fossa, is an area in the deep face known as the infratemporal fossa, outlined in dashed lines on the lower image. Note that the zygomatic arch and mandible have been removed in this image. The infratemporal fossa is bounded laterally by the mandibular ramus, medially by the lateral pterygoid plate, anteriorly by the maxilla, and posteriorly by the styloid and mastoid processes.

• The infratemporal fossa contains the medial and lateral pterygoid muscles, tendon of the temporalis muscle, maxillary artery and pterygoid venous plexus, and branches of cranial nerve (CN) V ₃ , chorda tympani, and otic ganglion.

• CN V ₃ enters the infratemporal fossa through the foramen ovale.

• The infratemporal fossa communicates with the pterygopalatine fossa through a teardrop-shaped opening called the pterygomaxillary fissure.

• The pterygopalatine fossa lies deep to the pterygomaxillary fissure. It contains CN V ₂ and many of its branches, the maxillary artery, and pterygopalatine ganglion.

• The pterygopalatine fossa communicates medially with the nasal cavity through the sphenopalatine foramen.

• You can think of the pterygopalatine fossa as a small room with multiple doors or openings in and out: the lateral door is the pterygomaxillary fissure; the medial door is the sphenopalatine foramen; and the anterior door is the inferior orbital fissure.

Lateral radiographs of the skull allow visualization of superficial and deep landmarks concurrently.

First, identify the coronal suture, which separates the frontal and parietal bones of the skull. The lambdoid suture is visible posteriorly, dividing the parietal from the occipital bones. Posterior and superficial to the lambdoid suture, note the external occipital protuberance on the occipital bone.

Note that pneumatized bones, such as the maxilla (containing maxillary sinus), frontal bone (containing frontal sinus), sphenoid bone (containing sphenoid sinus), and mastoid process (containing mastoid air cells), appear radiolucent, or darker, than surrounding areas of the skull.

Superior to the sphenoid sinus, the bony sella turcica houses the pituitary gland. Anterior to the sella turcica, the greater wing of the sphenoid bone is visible.

Note the components of the mandible, including the more anteriorly positioned coronoid process and the more posteriorly located condyle.

The cervical spine is also apparent, with the anterior arch of atlas (C1) and dens of axis (C2) clearly delineated.

The upper image illustrates a sagittal section through the cranial fossae, nasal cavity with nasal septum in place, and hard palate.

• In the floor of the cranial cavity, the boundaries of the anterior, middle, and posterior cranial fossae are clearly delineated.

• The anterior cranial fossa extends from the frontal bone to the lesser wing of the sphenoid bone and includes the ethmoid bone. Visible within the anterior cranial fossa is the crista galli, a bony projection from the ethmoid bone that serves as an attachment for the cerebral falx, a dural fold that separates the cerebral hemispheres. On either side of the crista galli, you can see the cribriform plate of the ethmoid bone, which transmits the central processes of cranial nerve (CN) I, the olfactory nerve.

• The middle cranial fossa is bounded by the greater wing of the sphenoid bone and extends posteriorly to the petrous ridge of the temporal bone. The sella turcica is located in the middle cranial fossa.

• The posterior cranial fossa extends posteriorly from the dorsum sellae of the sphenoid bone. The posterior cranial fossa is bounded by the petrous and tympanic portions of the temporal bone and by the occipital bone.

The lower image demonstrates the composition of the lateral nasal wall.

• The lateral nasal wall is formed by the nasal, frontal, lacrimal, ethmoid, palatine, and sphenoid bones, along with the maxilla and inferior concha.

• The ethmoid bone is specialized to form the superior and middle conchae, which are scroll-shaped bones that extend medially into the nasal cavity. The inferior concha is a separate bone. All the nasal conchae are covered by respiratory mucosa. They function to increase the surface area over which air is warmed and humidified before entering the lungs and to create turbulence in inspired air.

• Located between the perpendicular plate of the palatine bone and the sphenoid bone is the sphenopalatine foramen, which allows communication between the nasal cavity and the more laterally positioned pterygopalatine fossa. This foramen conveys the sphenopalatine artery, a branch of the maxillary artery, along with branches of CN V ₂ , including the posterolateral nasal nerves and nasopalatine nerve.

The upper image is a superior view of the calvaria, which forms the roof of the neurocranium.

The calvaria is formed by the frontal bone anteriorly, the two parietal bones laterally, and the occipital bone posteriorly. The frontal and parietal bones articulate by way of the coronal suture, while the parietal bones unite at the sagittal suture. The lambdoid suture is formed by the articulation of the parietal and occipital bones posteriorly.

Diploë is the bone marrow of the calvarial bones. Diploic veins are large, thin-walled vessels that may drain internally into one of the dural venous sinuses or externally into the occipital vein.

The lower image shows the deep surface of the calvaria that faces the brain and its meningeal coverings.

On the deep surface of the calvaria, a deep midline groove for the superior sagittal dural venous sinus is visible, running anterior to posterior. Just lateral to this groove, a series of small pits, known as granular foveolae, are created by pressure on the bone by arachnoid granulations, which are aggregates of arachnoid mater that protrude through the dura mater into the superior sagittal sinus and its lateral lacunae.

On the lateral sides of the deep surface of the calvaria, note the grooves for branches of the middle meningeal arteries, which mainly supply the periosteum of the bones of the calvaria, as well as the dura.

The inferior surface of the cranial base is formed by the maxilla, palatine, vomer, sphenoid, temporal, and occipital bones.

Anteriorly, the hard palate is formed by the palatine process of the maxilla and the horizontal plate of the palatine bone.

• The incisive fossa, located posterior to the central incisors, conveys the nasopalatine nerve, a sensory nerve that supplies the anterior mucosa of the hard palate.

• The horizontal plates of the palatine bone unite posteriorly to form the posterior nasal spine, to which the uvula of the soft palate is attached.

• Note the position of the greater and lesser palatine foramina, which convey neurovasculature to the hard and soft palatine mucosae, respectively.

The vomer extends superiorly from the posterior aspect of the hard palate. It contributes to the bony component of the nasal septum and creates two choanae, or internal nares, that allow for communication between the nasopharynx and the nasal cavities.

Inferiorly, the pterygoid processes and the greater wings of the sphenoid bone are visible.

• Each pterygoid process consists of a medial and lateral pterygoid plate, separated by the pterygoid fossa. Inferior to the pterygoid fossa is a small, canoe-shaped depression known as the scaphoid fossa. The medial pterygoid plate has a hook, or hamulus, projecting from its inferior surface.

• The greater wing of the sphenoid bone forms the superior boundary of the infratemporal fossa below. The foramen ovale and foramen spinosum are visible in the medial aspect of the greater wing and serve as communication sites between the middle cranial fossa and the infratemporal fossa.

The temporal bone exhibits several specializations from the inferior view, including the more medial, rock-like petrous portion and the more lateral, smooth squamous portion.

• The mandibular fossa of the temporal bone serves as a site of articulation for the condylar head of the mandible, forming the temporomandibular joint. The petrotympanic fissure is visible just posterior to the mandibular fossa and serves as the exit point for the chorda tympani nerve of cranial nerve (CN) VII as it travels into the infratemporal fossa.

• The carotid canal is located in the petrous portion of the temporal bone and serves as the entrance point for the internal carotid artery into the skull base.

• Two processes characterize the inferior surface of the temporal bone: styloid and mastoid.

  • The styloid process of the temporal bone projects inferiorly and serves as a site of attachment for a variety of muscles (e.g., stylohyoid, styloglossus, stylopharyngeus) and the stylohyoid ligament.

  • The mastoid process serves as an attachment for the sternocleidomastoid splenius capitis muscles. Just medial to this process, the mastoid notch is visible, which serves as an attachment site for the posterior belly of the digastric muscle.

  • Between the styloid and mastoid processes, the stylomastoid foramen transmits the facial nerve and stylomastoid artery.

At the cranial base, the occipital bone surrounds a large opening, the foramen magnum, which contains and marks the transition between the cervical spinal cord and the medulla oblongata of the brain stem.

• Anterior to foramen magnum, the basilar portion of the occipital bone is characterized by the pharyngeal tubercle, to which the superior pharyngeal constrictor muscle is attached.

• The foramen lacerum is located between the basilar and petrous portions of the temporal bone and the pterygoid process of the sphenoid bone. The greater petrosal nerve travels superior to this opening in the skull, which is almost completely closed by a fibrocartilaginous plug in life.

• The occipital condyles lie just lateral to foramen magnum and articulate with the first cervical vertebra (C1).

• The hypoglossal canal is located just anterolateral to the occipital condyles, and it conveys CN XII, the hypoglossal nerve.

• The jugular foramen is located lateral to the occipital condyles, between the petrous temporal and occipital bones. It transmits the internal jugular vein and CNs IX, X, and XI.

• When present, the posterior condylar canal is located posterior to the occipital condyles and transmits emissary veins from the sigmoid dural venous sinus to the occipital veins of the scalp.

• The external occipital protuberance is a prominent landmark on the posterior aspect of the occipital bone. It serves as an attachment for the trapezius muscle. Extending laterally from this midline structure is the superior nuchal line, to which trapezius and sternocleidomastoid muscles are attached.

Examination of the cranial base from a superior view reveals the organization of this area into three fossae: anterior, middle, and posterior.

The anterior cranial fossa is formed by the frontal, ethmoid, and sphenoid bones. The posterior border of the anterior cranial fossa is marked by the lesser wing of the sphenoid. The ethmoid bone contains two specializations in this region: the cribriform plate, which conveys the olfactory cranial nerve, and the crista galli, to which the cerebral falx is attached.

The middle cranial fossa is formed by the sphenoid, temporal, and parietal bones.

• The greater wing of the sphenoid contains several key foramina in this region, including the rotundum, ovale, and spinosum. The foramen rotundum conveys cranial nerve (CN) V ₂ , the foramen ovale conveys CN V ₃ and lesser petrosal nerve, and the foramen spinosum conveys the middle meningeal artery. Grooves created by this artery in the sphenoid, temporal, and parietal bones are visible extending anteriorly and laterally from the foramen spinosum.

• The superior orbital fissure and optic canal are considered to be in the middle cranial fossa.

• The pituitary gland is located centrally in the middle cranial fossa, specifically in a depression in the sphenoid bone known as the hypophyseal fossa. If this fossa is considered as a “bed” for the pituitary gland, the front of the bed frame is the tuberculum sellae, and the headboard is the dorsum sellae. The four bedposts include the anterior and posterior clinoid processes. The term sella turcica refers to the saddle-like bony structure in which the hypophyseal fossa is located; it includes the tuberculum sellae and dorsum sellae.

The posterior cranial fossa is formed by the petrous temporal, parietal, and occipital bones.

• The internal acoustic meatus, jugular foramen, hypoglossal canal bilaterally, and the foramen magnum in the midline all communicate with the posterior cranial fossa. CNs VII and VIII travel through the internal acoustic meatus. The internal jugular vein and CNs IX, X, and XI travel through the jugular foramen. CN XII travels through the hypoglossal canal.

• The posterior cranial fossa contains several dural venous sinuses, with associated bony landmarks. The internal occipital protuberance of the occipital bone marks the site for the confluence of the sinuses; grooves for the transverse sinuses extend laterally from this bony landmark. The transverse sinuses drain to the sigmoid sinuses on each side, which become the internal jugular veins within the jugular foramina. A small, occipital dural venous sinus creates a groove just posterior to the foramen magnum as this sinus approaches the confluence.

A variety of neurovascular elements enter and exit the cranial base through foramina, fissures, canals, and canaliculi.

From an inferior view, proceeding anterior to posterior along the cranial base, the first opening encountered is the incisive fossa in the maxillary bone. It conveys the nasopalatine nerve, a branch of cranial nerve (CN) V ₂ that originates in the pterygopalatine fossa, enters the nasal cavity via the sphenopalatine foramen, and travels along the nasal septum until it reaches the incisive canal and fossa. The nasopalatine nerve supplies the anterior aspect of the hard palate with sensory innervation. A branch of the sphenopalatine artery accompanies the nasopalatine nerve along the nasal septum to the incisive canal and fossa.

Next, the greater and lesser palatine foramina are visible.

• The greater palatine foramen is located between the palatine and maxillary bones and conveys the greater palatine nerve and vessels to the hard palate posterior to the canine teeth.

• The lesser palatine foramen is located in the pyramidal process of the palatine bone and conveys the lesser palatine nerve and vessels to the soft palate.

Posterior to the medial pterygoid plate of the sphenoid bone, the foramen lacerum is visible medial to the petrous temporal bone and lateral to the basilar occipital bone. It is covered by a fibrocartilaginous plate in life, and the greater petrosal nerve of CN VII travels across it superiorly.

Lateral to the foramen lacerum, the foramen ovale and foramen spinosum can be identified.

• The foramen ovale contains CN V ₃ as it enters the infratemporal fossa, the lesser petrosal nerve of CN IX, and the accessory middle meningeal artery.

• The foramen spinosum conveys the middle meningeal vessels and a meningeal branch of V ₃ .

Posterior to the foramen spinosum, the carotid canal can be seen. It carries the internal carotid artery as it enters the skull base and the sympathetic carotid plexus of nerves coating the artery.

Lateral to the carotid canal is the petrotympanic fissure, located just posterior to the mandibular fossa of the temporal bone. This fissure transmits the chorda tympani branch of CN VII, carrying preganglionic parasympathetic fibers destined to synapse in the submandibular ganglion, along with taste fibers from the anterior two thirds of the tongue.

Moving posteriorly, the stylomastoid foramen transmits CN VII after it has traversed the length of the facial canal.

Medial to the stylomastoid foramen, the mastoid canaliculus transmits the sensory auricular branch of CN X. The tympanic canaliculus conveys the tympanic branch of CN IX, which carries preganglionic parasympathetic fibers destined to synapse in the otic ganglion and sensory fibers for the middle ear cavity.

The jugular foramen lies just posterior to the canaliculi and transmits CNs IX, X, and XI and the internal jugular vein.

The hypoglossal canal is located medial to the jugular foramen. It transmits the hypoglossal nerve, which innerves all the intrinsic and most of the extrinsic muscles of the tongue (except palatoglossus, a muscle of the palate supplied by CN X).

The foramen magnum lies in the midline of the squamous part of the occipital bone and conveys the medulla of the brain stem and the vertebral arteries and veins, along with CN XI as it ascends from the spinal accessory nucleus.

A variety of neurovascular elements enter and exit the cranial base through foramina, fissures, and canals.

From a superior view, anterior to posterior along the cranial base, the first opening encountered in the anterior cranial fossa is the foramen cecum, formed by the articulation of the caudal end of the frontal crest with the crista galli of the ethmoid bone. The foramen cecum transmits an emissary vein from the nasal cavity to the superior sagittal sinus.

The nasal slit is located posterolateral to the foramen cecum: it conveys sensory fibers and blood vessels to the nasal cavity from the anterior ethmoidal nerve (from the nasociliary nerve of CN V ₁ ) and occasionally accommodates a vein draining from the nasal mucosa to the superior sagittal sinus.

The anterior ethmoidal foramen is located at the junction of the ethmoid and frontal bones and transmits the anterior ethmoidal neurovasculature from the anterior cranial fossa to the nasal cavity.

The cribriform plate of the ethmoid bone is located just lateral to the crista galli and conveys cranial nerve (CN) I from the olfactory epithelium of the nasal cavity to the olfactory bulb.

The posterior ethmoidal foramen is located at the junction of the ethmoid and frontal bones and transmits the posterior ethmoidal neurovasculature from the anterior cranial fossa to the nasal cavity.

Moving posteriorly into the middle cranial fossa, the optic canal is the site through which CN II and the ophthalmic artery communicate with the orbit.

Just lateral to the optic canal, the diagonal gap between the greater and lesser wings of the sphenoid bone form the superior orbital fissure. It transmits the motor nerves to the extraocular muscles (CNs III, IV, and VI), CN V ₁ , and the ophthalmic veins.

Posterior to the superior orbital fissure, the foramen rotundum transmits V ₂ to the pterygopalatine fossa anteriorly.

The foramen ovale lies posterolateral to the foramen rotundum. It contains CN V ₃ , the lesser petrosal nerve of CN IX, and the accessory meningeal artery.

Medial to the foramen ovale, the carotid canal opens superiorly into the middle cranial fossa, conveying the internal carotid artery and its sympathetic carotid plexus. The foramen lacerum can be seen medial to the superior opening of the carotid canal.

Posterolateral to the carotid canal are two small, hiatal grooves for the greater and lesser petrosal nerves as they exit the temporal bone to enter the middle cranial fossa.

• The greater petrosal nerve branches from CN VII at the level of the geniculate ganglion in the temporal bone.

• The lesser petrosal nerve emerges from the tympanic plexus in the middle ear cavity in the temporal bone.

Posterolateral to the carotid canal, the internal acoustic meatus provides an opening into the temporal bone through which CNs VII and VIII and the labyrinthine artery travel. The labyrinthine artery supplies the inner ear and is typically a branch of the basilar artery but may arise from the anterior inferior cerebellar artery.

Posterolateral to the internal acoustic meatus is the opening of the vestibular aqueduct. This passageway transmits the endolymphatic duct, which connects the saccule of the membranous labyrinth of the inner ear to the endolymphatic sac, a blind-ended reservoir for endolymph in the posterior cranial fossa.

The jugular foramen lies posterior to the internal acoustic meatus. It conveys CNs IX, X, and XI and the internal jugular vein, or it conveys the structures forming it (inferior petrosal and sigmoid sinuses) if the internal jugular vein forms just below the jugular foramen. The posterior meningeal artery, a branch of the ascending pharyngeal artery, may traverse the jugular foramen to supply the dura mater of the posterior cranial fossa.

The hypoglossal canal lies medial to the jugular foramen and transmits CN XII.

The foramen magnum lies in the midline of the squamous occipital bone and transmits the medulla oblongata of the brain stem, vertebral arteries and veins, and CN XI as it ascends from the spinal accessory nucleus.

The bones of the fetal skull develop by two different processes, depending on their location. Most of the calvaria is formed by intramembranous ossification, whereas most of the skull base is formed by endochondral ossification.

The newborn skull is characterized by prominent eminences in the frontal and parietal bones. The facial skeleton of a newborn is disproportionately small relative to the adult facial skeleton. Wide fibrous membranes forming soft spots, or fontanelles, are present; they are functionally important during vaginal birth, allowing the calvarial bones to shift to negotiate the birth canal during vaginal delivery. Clinically, fontanelles are important to evaluate the growth of certain skull bones, hydration status, and intracranial pressure of the newborn and infant.

The frontal bones are divided by the frontal suture; the parietal bones are separated by the sagittal suture posteriorly. The frontal and parietal bones are separated by the coronal suture, and the parietal and occipital bones by the lambdoid suture. The squamous suture divides the squamous portions of the parietal and temporal bones.

The anterior fontanelle is a diamond-shaped region between the frontal and parietal bones, and its location corresponds to the bregma, where the coronal and sagittal sutures meet in the mature calvaria.

The posterior fontanelle is a triangular-shaped region between the parietal and occipital bones, and its location corresponds to the lambda, where the lambdoid sutures meet in the mature skull.

The sphenoid and mastoid fontanelles are united by the squamous suture.

Typically, the posterior fontanelle closes in the first 3 months postnatally, followed by the sphenoid and mastoid fontanelles. The anterior fontanelle is the last to close, most by the middle of the second year, and almost all by 24 months.

The skeletal framework of the head and neck consists of the skull, mandible, hyoid bone, cervical vertebrae, manubrium of the sternum, and the clavicle. The cartilaginous larynx and trachea are palpable in the neck.

On this lateral view of the head, the anatomical relationships of the mandible are clearly visible. Superiorly, the anterior coronoid and posterior condylar processes are shown, with the mandibular notch between them. These two processes unite as the vertically oriented ramus of the mandible. The ramus joins the more horizontally oriented mandibular body at the angle of the mandible, typically positioned at vertebral level C2.

The hyoid bone is located inferior to the mandible, typically at vertebral level C3.

The larynx lies just inferior to the hyoid bone and spans vertebral levels C3‒6. The thyroid cartilage is typically positioned at vertebral level C4‒5; the cricoid cartilage lies at vertebral level C6.

Posterior to the mandible, the external acoustic meatus is clearly visible on the lateral aspect of the temporal bone; the styloid process is located just inferior to the meatus.

A number of ligaments support the bony framework of the head and neck, as demonstrated.

• The stylomandibular ligament spans between the styloid process of the temporal bone and the angle of the mandible. Its position and orientation indicate that this ligament cannot mechanically constrain any normal movements of the mandible.

• The stylohyoid ligament spans between the styloid process of the temporal bone and the lesser horn of the hyoid bone. It can become ossified in a condition known as Eagle syndrome, resulting in compression of cranial nerves V, VII, IX, and X or the internal carotid artery.

• The pterygomandibular raphe is shown in phantom, attached between the hamulus of the medial pterygoid plate and the retromolar triangle of the mandible. This raphe serves as a point of attachment for the buccinator muscle anteriorly and the superior pharyngeal constrictor posteriorly.

This plate demonstrates a coronal section through the facial skeleton, at the level illustrated in the upper right image of this plate.

In the lower image of this plate, first note the skull region superior to the bony orbits, the region known as the anterior cranial fossa. In this fossa of the skull, identify the crista galli and cribriform plate of the ethmoid bone. Cranial nerve I sends its axons through the cribriform plate to synapse in the olfactory bulb in the anterior cranial fossa.

Follow the crista galli inferiorly as it forms the perpendicular plate of the ethmoid bone, which creates the upper bony part of the nasal septum. This perpendicular plate of the ethmoid blends inferiorly with the vomer, which attaches to the bony palate. The bony part of the nasal septum divides the nasal cavity into right and left sides.

The lateral wall of each side of the nasal cavity is characterized by scroll-shaped bony projections known as nasal conchae, which increase the surface area within the nasal cavity. When these conchae are covered by highly vascular respiratory epithelium, the capacity to warm and humidify inspired air is significantly increased.

The superior and middle nasal conchae are part of the ethmoid bone, whereas the inferior concha is a distinct bone. Inferior to each concha is a compartment within the nasal cavity known as a meatus.

The superior meatus (SM) lies inferior to the superior concha, the middle meatus (MM) is located inferior to the middle concha, and the inferior meatus (IM) lies inferior to the inferior concha.

Closely associated with the nasal cavity are the paranasal sinuses, which are air-filled extensions of the nasal cavity into the bones of the skull, including the ethmoid bone and maxilla. In this image, the ethmoidal cells are visible on the medial aspect of each orbit. The sinus of the maxilla is also visible inferior to each orbit. Note the opening of the sinus of the maxilla medially into the MM.

Demonstrates the pterygoid and infratemporal fossae and their superficial and deep relationships.

The upper image shows the skull base with the mandible removed. For orientation, find the external occipital protuberance, or inion, with the superior nuchal lines extending laterally from it on each side. Note the mastoid and styloid processes of the temporal bone and the zygomatic arches bilaterally. The occipital condyles are also visible in this view.

• Just inferior to the occipital condyles, note the two pterygoid plates of the sphenoid bone (medial and lateral) and the space between them, termed the pterygoid fossa. The medial pterygoid muscle fills much of the pterygoid fossa on each side.

• The medial pterygoid plate terminates in a bony hook, the hamulus, which is grooved anteriorly by the tendon of the tensor veli palatini muscle.

• Medial to the medial pterygoid plate, note the choanae, or posterior openings into the nasal cavities. These two openings are separated by the vomer of the nasal septum. When you look through the choanae, the middle and inferior conchae, which are scroll-shaped bony projections, are visible on the lateral nasal wall bilaterally.

• The two components of the hard palate can be seen in the upper image, including the horizontal plate of the palatine bone and the palatine process of the maxilla. The incisive fossa, which conveys the nasopalatine nerve to the mucosa of the anterior part of the hard palate, is visible in the midline just posterior to the central incisors.

The lower image clearly demonstrates the infratemporal fossa and its relationship to deeper regions in the head. Note that the mandible has been removed in this image.

• The infratemporal fossa is located deep to the ramus of the mandible and medial to the lateral pterygoid plate. Its anterior boundary is the posterior aspect of the maxilla, and its posterior boundary is formed by the mastoid and styloid processes of the temporal bone. Superiorly, the infratemporal fossa extends to the inferior surface of the greater wing of the sphenoid bone.

• The infratemporal fossa communicates with the deeper pterygopalatine fossa through a planar, door-like opening, the pterygomaxillary fissure. The pterygopalatine fossa is a small region medial to the infratemporal fossa and inferior to the apex of the orbit. It contains several foramina, including the sphenopalatine foramen communicating with the nasal cavity.

The mandible forms the skeleton of the chin. It is a horseshoe-shaped bone with a horizontally oriented body anteriorly. The body turns posteriorly and superiorly at the angle of the mandible to form the ramus. Superiorly, the ramus ends in two processes, a more anterior coronoid process and a posterior condylar process.

The coronoid process serves as an attachment for the temporalis muscle.

The condylar process includes the condylar head, which articulates with the mandibular fossa of the temporal bone to form the temporomandibular joint. The condylar head tapers inferiorly to form the condylar neck, which contains a small depression, the pterygoid fovea, where the lateral pterygoid muscle is partially attached.

The mental protuberance is a midline elevation on the superficial surface of the mandibular body that forms the prominence of the chin. This bony landmark is bounded laterally on each side by a mental tubercle.

Moving posteriorly along the body of the mandible, the mental foramen is the next characteristic feature encountered; this opening transmits the inferior alveolar nerve and vessels.

• The oblique line is a bony ridge visible on the superficial surface of the mandible, extending from the anterior border of the ramus to the mental tubercle on each side.

• Medial to the oblique line as it takes origin from the anterior part of the ramus, the retromolar fossa can be visualized; this is an important landmark when administering an inferior alveolar nerve block.

On the deep surface of the mandible, in the midline, two to four small, bony bumps can usually be identified. These are the genial tubercles, or mental spines; they are attachment sites for genioglossus (superior genial tubercles) and geniohyoid (inferior genial tubercles) muscles.

Extending laterally from the midline of the deep surface of the mandibular body is the mylohyoid line, which serves as an attachment for the mylohyoid muscle. The mylohyoid line separates a superior depression, the sublingual fossa (which houses the sublingual salivary gland), from an inferior depression, the submandibular fossa (which houses the submandibular salivary gland).

Moving superiorly up the deep surface of the mandibular ramus, the next key landmark is the mandibular foramen, which transmits the inferior alveolar nerve and vessels that supply the mandibular teeth and exit the mental foramen superficially as the mental nerve and vessels. The mandibular foramen is guarded anteriorly by a bony, tongue-like projection known as the lingula. The sphenomandibular ligament is attached to the lingula.

The lower right image shows the mandible of an edentulous patient. Note the position of the mental foramen on this mandible; resorption of the alveolar ridge as a result of tooth loss can destroy the mental foramen, leaving the mental neurovasculature unprotected and prone to injury.

The upper figure summarizes the 20 deciduous, or primary, teeth in children and their timeline for eruption. The deciduous teeth include the central and lateral incisors, canine, and first and second molars on each side of the maxillary and mandibular arches.

• The incisors are first to erupt, usually at 8 to 10 months on the maxillary arch and 6 to 21 months on the mandibular arch.

• Canines and first molars erupt next, usually at 15 to 21 months on the maxillary and mandibular arches.

• The molars are the last teeth to erupt, usually at 15 to 24 months on the maxillary and mandibular arches.

The permanent, or secondary, teeth are shown in blue and include the central and lateral incisors, canine, first and second premolars, and first, second, and third molars on each side of the maxillary and mandibular arches.

• The first molars are the first teeth to erupt, typically at age 6 years on the maxillary and mandibular arches.

• The incisors erupt typically at 7 to 8 years on the maxillary and mandibular arches.

• The premolars erupt next, typically 9 to 10 years on the maxillary and mandibular arches.

• The second molars typically erupt at age 10 years, while the canines erupt at 11 to 12 years.

• The third molars (wisdom teeth) erupt last, usually at age 17 to 25.

The position of the permanent teeth is shown in the lower figures, with the maxillary arch to the left and the mandibular arch to the right.

• The incisors are the most anterior teeth, with the central incisors being most anterior and lateral incisors positioned posterior to them. Posterior to the incisors are the canines, premolars (first anterior to second), and most posteriorly, the molars (with first being most anterior and third most posterior).

The upper image shows the general histological organization of a tooth.

• Each tooth consists of a crown, neck, and root. The crown extends superior to the gingiva. The neck is the transitional area between the crown and root. The root is anchored into the alveolar bone by the periodontium.

• Dentin covers the tooth in its entirety, while enamel covers the crown and cement covers the root. A pulp cavity within the dentin contains vessels and nerves. This pulp cavity narrows inferiorly to form the root canal that allows the entry and exit of the neurovascular elements through the apical foramen.

The lower image shows the anatomy of each of the permanent teeth.

• The incisors have a sharp cutting surface and a single root.

• The canines are positioned at the corners of each dental arch and have a sharp, pointed occlusal surface and a single root.

• The premolars have a flat biting surface and one or two roots (maxillary first premolars typically have two roots).

• The molars are the largest of the teeth, with a flat occlusal surface and two or three roots (maxillary molars typically have three roots).

The temporomandibular joint (TMJ) is a synovial joint between the mandibular fossa of the temporal bone and the condylar head of the mandible. As with any synovial joint, the TMJ has a fibrous joint capsule, which here attaches along the temporal bone and to the mandibular neck. Unlike most synovial joints, however, its articular surfaces are lined by fibrocartilage, rather than hyaline cartilage, and the TMJ cavity is divided into upper and lower compartments (“spaces”) by a fibrocartilaginous articular disc.

On this lateral view, you can see the lateral ligament, a thickening of the joint capsule, which helps to prevent posterior dislocation of the TMJ.

Also visible are two extrinsic ligaments outside the joint capsule, the stylomandibular and sphenomandibular ligaments.

• The stylomandibular ligament runs from the styloid process of the temporal bone to the angle of the mandible.

• The sphenomandibular ligament spans from the spine of the sphenoid to the lingula of the mandible.

These two extrinsic ligaments can be more readily visualized from a medial view. Although the stylomandibular ligament does not provide substantive support to the TMJ, the sphenomandibular ligament is the primary passive support of the mandible.

Note that the inferior alveolar nerve, a branch of cranial nerve (CN) V ₃ , travels between the sphenomandibular ligament and the ramus of the mandible to gain access to the mandibular foramen. This ligament can block the diffusion of local oral anesthetic administered during an inferior alveolar nerve block, resulting in difficulty in numbing the patient’s mandible.

The primary sensory nerve of the TMJ is the auriculotemporal nerve, together with branches from the masseteric and deep temporal nerves; all are branches of CN V ₃ . The auriculotemporal nerve can be seen branching posteriorly from V ₃ and traveling around the mandibular neck before ascending anterior to the external ear.

The mandibular fossa and condylar head are completely separated by an articular disc, which divides the joint cavity into two discrete spaces where different types of movement occur. Protrusion and retrusion, sometimes referred to as translation or gliding motions, occur between the mandibular fossa and articular disc. Elevation, depression, and rotation occur between the articular disc and the condylar head.

When the jaw is closed, the condylar heads are held in a retracted position in the mandibular fossae. When the jaw slightly opens, the hinge action predominates. As the mouth opens wider, gliding allows the mandible to move forward, or protrude.

Popping or clicking in the TMJ may result if the articular disc does not stay in place between the condylar head and mandibular fossa.

The two most superior cervical vertebrae are highly specialized to accommodate the articulation of the skull with the vertebral column.

The first cervical vertebra (C1) is also known as the atlas because of its similarity to the Greek god Atlas holding the world (skull) on his shoulders.

• The atlas is unique among cervical vertebrae because it lacks a vertebral body and a spinous process.

• The atlas consists of two lateral masses, each of which has a superior articulating facet for the occipital condyle of the skull. A transverse process projects laterally from each lateral mass, with a transverse foramen (foramen transversarium) to transmit the vertebral artery.

• The lateral masses are connected by anterior and posterior arches, which complete the bony ring.

  • Each arch has a tubercle that serves as an attachment for ligaments: anterior longitudinal ligament for anterior tubercle and nuchal ligament (ligamentum nuchae) for posterior tubercle.

  • As the vertebral artery emerges from the transverse foramen of C1, it lies in a groove on the superior surface of the posterior arch en route to the foramen magnum of the skull.

The second cervical vertebra (C2) is also known as the axis because it forms the pivot around which the atlas rotates.

• The axis has a body and a bifid spinous process. A tooth-like projection known as the dens, or odontoid process, projects superiorly from the vertebral body. The dens acts as the pivot around which rotation of the head takes place. It is stabilized against the anterior arch of C1 by the transverse ligament of the atlas.

• The axis has both a superior and an inferior articulating facet, between which lies the pars interarticularis. The superior articulating facet of the axis articulates with the inferior articulating facet of C1, while the inferior articulating facet of the axis articulates with the superior articulating facet of C3.

The third (C3) through sixth (C6) cervical vertebrae exhibit typical features for cervical vertebrae.

Standard cervical vertebrae have a small vertebral body, characterized by uncinate processes, which are superior elevations on each side.

• The uncinate processes are separated by intervertebral discs under normal circumstances, creating uncovertebral joints (clefts/crypts of Luschka). With age, however, the intervertebral discs degenerate, resulting in the direct approximation of the bony uncinate process of one vertebral body with that of the next more superior vertebra.

C3 to C7 also exhibit a vertebral arch that extends posterior to the vertebral body.

• The vertebral arch is formed by two laminae that unite with the spinous process and the pedicles that connect directly to the vertebral body. The spinal cord occupies the space bounded by the vertebral arch, known as the vertebral canal.

• All cervical vertebrae have a vertebral canal that is large relative to the overall size of the vertebra in order to accommodate the cervical enlargement of the spinal cord.

Standard cervical vertebrae have transverse processes with a transverse foramen (foramen transversarium) that conveys the V ₂ segment of the vertebral artery (except C7) and the vertebral veins. The transverse processes of typical cervical vertebrae display anterior and posterior tubercles, which serve as attachment sites for lateral neck and deep back musculature.

• The anterior tubercles of C6 may be referred to as carotid tubercles because of their close anatomical relationship with the common carotid arteries, and they are palpable.

Bifid spinous processes are unique features of C2 to C6.

C7 has a long, single spinous process, usually visible when the neck is flexed, giving this vertebra the name vertebra prominens.

Demonstrates an anterior view of a fully articulated cervical spine (upper image) and a coronal section through C3‒7 vertebrae (lower image).

In the upper image, the anterior arch of the atlas is visible, with its anterior tubercle for attachment of the anterior longitudinal ligament. Transverse processes extend laterally, containing transverse foramina that transmit the V ₂ segment of the vertebral artery and the vertebral veins. Note the absence of an intervertebral disc between the atlas and axis.

For C3 to C7, uncinate processes project superiorly on the lateral sides of each vertebral body.

Normally, the uncinate processes are separated by intervertebral discs, creating uncovertebral joints (clefts of Luschka). With age, the intervertebral discs degenerate, resulting in the direct approximation of the bony uncinate process of one vertebral body with that of the next, more superior vertebra.

Two sets of synovial craniocervical (craniovertebral) joints allow movement between the skull and neck. The atlantooccipital joints, located between C1 and the skull base, allow nodding the head up and down to indicate “yes.” The atlantoaxial joints, located between C1 and C2, allow shaking the head from side to side to indicate “no.” Several ligaments visible are associated with these joints and help to stabilize the skull on the cervical spine.

In the upper image, the anterior view shows the joint capsules of both the atlantooccipital and the atlantoaxial joint. The capsules are lax and loosely arranged to allow for adequate movement within each joint. The anterior atlantooccipital membrane spans from the anterior arch of C1 to the foramen magnum; note how its fibers blend with those of the anterior longitudinal ligament below. The anterior membrane is effective in preventing excessive movement at the atlantooccipital joint.

In the middle right image, the posterior view shows the posterior atlantooccipital membrane spanning from the posterior arch of C1 to the foramen magnum and its relationship to the V ₄ segment of the vertebral artery as it pierces the inferior border of the posterior atlantooccipital membrane to reach the cranial cavity. This image also illustrates the continuity of the ligamentum flava (between adjacent laminae inferiorly) with the posterior atlantooccipital membrane superiorly.

In the lower image, the right lateral view depicts the relationship between the longitudinal ligaments and craniocervical ligaments.

Note the course of the V ₂ to V ₄ segments of the vertebral artery.

Demonstrates the craniocervical ligaments visible within the vertebral canal.

The upper image is a posterior view into the vertebral canal and cranial cavity, with the spinous processes and posterior skull base removed. The vertebral bodies of the cervical vertebrae are anterior to the tectorial membrane and posterior longitudinal ligament. The capsules of the atlantooccipital and atlantoaxial joints are seen laterally on either side of the tectorial membrane.

The posterior longitudinal ligament is renamed the tectorial membrane at the level of C2. The tectorial membrane is a strong, broad band that extends from the vertebral body of C2 through the foramen magnum to attach superiorly to the occipital bone, where it blends with the cranial dura mater.

The right upper image is the same view as the left upper image, except that most of the tectorial membrane has been removed to demonstrate the more anterior ligaments: the alar, cruciate, and apical ligaments.

The alar ligaments extend from the lateral sides of the dens of C2 to the edges of the foramen magnum. They are so named because they resemble wings extending from the dens. The alar ligaments can be seen isolated in the left lower image; they are important for checking and limiting rotation.

The cruciate ligament, so named because it forms a cross-like configuration, is composed of the transverse ligament of the atlas and the superior and inferior longitudinal bands.

• The transverse ligament of the atlas helps to support the dens of C2 in place against the anterior arch of C1; it extends between small tubercles on the medial aspects of each lateral mass of C1 (right lower image).

• The median superior and inferior longitudinal bands of the cruciate ligament extend from the transverse ligament of the atlas to the anterior rim of the foramen magnum superiorly and to the body of C2 inferiorly. The superior ligament is stronger than the inferior ligament.

The apical ligaments of the dens extend from the dens to the anterior margin of the foramen magnum. They are developmental remnants of the notochord and provide minimal support to the craniocervical joints.

The muscles of facial expression are organized into groups, acting on the scalp, forehead and eyebrows, eyelids, nostrils, lips, and skin of the anterior neck. They are unique in that they are only attached to bone at one end and to subcutaneous tissues at the other end.

In terms of muscles acting on the scalp, forehead, and eyebrows, the occipitofrontalis muscle consists of two muscle bellies (frontalis and occipitalis) connected by the epicranial aponeurosis. This muscle acts to wrinkle the forehead, raise the eyebrows, and retract the scalp.

Movement of the auricle is minimal in most people.

In terms of muscles acting on the eyelids, the orbicularis oculi forms a sphincter around each orbit and acts to close the eyelids, as in blinking.

The vertically oriented fibers of the procerus muscle act to wrinkle the skin over the bridge of the nose. The corrugator supercilii creates vertical wrinkles in the skin above the nose and between the eyebrows; it acts with the orbicularis oculi to draw the eyebrows medially and downward when shielding the eyes from bright light and when frowning. The alar fibers of the nasalis muscle are active before inspiration and flare the nostrils.

In the region of the lips, muscles of facial expression insert into either the upper or the lower lip, or into the region of the corner of the mouth known as the modiolus.

The orbicularis oris muscle forms a sphincter around the lips and acts to close the oral fissure when approximating the lips. The levator labii superioris and zygomaticus minor elevate the upper lip, while the zygomaticus major elevates the labial commissure (corner of the mouth). The risorius is a highly variable muscle that pulls the corners of the mouth laterally in numerous facial activities, including smiling and laughing. Strictly speaking, the buccinator is not a muscle of facial expression; it is the cheek muscle that functions to tighten the cheek against the molar teeth to prevent food from entering the oral vestibule while eating.

The platysma muscle arises from the fascia over the upper parts of the pectoralis major and deltoid and is attached to the lower border of the mandible and the skin and subcutaneous tissues of the lower face. The platysma may assist in depressing the mandible. The depressor anguli oris lowers the corner of the mouth; the depressor labii inferioris lowers the inferior lip; and the mentalis muscle protrudes the lower lip.

On the right side, note the layers of deep fascia.

• The cut edge of the platysma muscle is shown. The underlying, investing layer of deep fascia splits to enclose the sternocleidomastoid and extends laterally to form the roof of the posterior triangle of the neck.

• The investing fascia extends superior to the hyoid bone, covering the suprahyoid muscles (digastric, mylohyoid, and stylohyoid). It has been cut in this view to reveal the underlying muscles.

• The potential space known as the suprasternal space (of Burns) is created by the attachment of the two layers of investing fascia to the manubrium.

• Deep to the investing layer of fascia, the middle (pretracheal) fascia is visible. Its muscular layer covers the infrahyoid muscles (sternohyoid, superior belly of omohyoid, sternothyroid, and thyrohyoid), and its visceral layer is visible in the midline covering the thyroid gland and trachea.

On the left side, the fascial layers have been removed to demonstrate the underlying muscles and vascular elements.

• The sternocleidomastoid muscle extends from the mastoid process of the temporal bone to the manubrium (sternal head) and the clavicle (clavicular head).

• The sternocleidomastoid is an important landmark in the neck, dividing it into anterior and posterior cervical triangles.

• The anterior triangle is bounded by the anterior border of the sternocleidomastoid posteriorly, lower border of the mandible superiorly, and midline of the neck. Its contents include the infrahyoid muscles, submandibular salivary gland, submental and submandibular lymph nodes, larynx, trachea, thyroid and parathyroid glands, common carotid artery, internal carotid artery, external carotid artery and its facial and lingual branches, internal and anterior jugular veins, hypoglossal nerve, and ansa hypoglossi.

• The posterior triangle is delineated by the posterior border of the sternocleidomastoid anteriorly, anterior border of the trapezius posteriorly, and middle third of the clavicle inferiorly. Its contents include the inferior belly of the omohyoid, scalene muscles, trunks of the brachial plexus, and accessory nerve.

The sternocleidomastoid muscle is reflected on the donor’s left side, while it is intact along with investing fascia on the donor’s right side.

The two major venous channels in the neck are the external and internal jugular veins. These veins are separated by the sternocleidomastoid muscle, with the external jugular vein being superficial to it and the internal jugular vein lying deep to it.

The retromandibular vein plays an important role in indirectly uniting the external and internal jugular venous systems.

• The retromandibular vein splits into anterior and posterior branches at the level of angle of the mandible.

• The posterior branch contributes to the external jugular vein, while the anterior branch joins the facial vein to form the common facial vein, which drains to the internal jugular vein.

The external jugular vein is formed superiorly by the union of the posterior branch of the retromandibular vein and the posterior auricular vein (not visible), at the level of the mandibular angle.

• The external jugular vein courses inferiorly over the sternocleidomastoid, and at the root of the neck, it pierces the investing fascia and passes deep to sternocleidomastoid to drain into the subclavian vein.

The anterior jugular veins are a common tributary of the external jugular veins.

• The anterior jugular veins originate near the hyoid bone in the region of the submental and submandibular triangles.

• They descend medial to the sternocleidomastoid and often unite in midline to form the jugular venous arch just superior to the manubrium of the sternum.

• The anterior jugular veins typically dive deep to the sternocleidomastoid on each side at the root of the neck to drain into either the external jugular vein or the subclavian vein.

The internal jugular vein is found deep to the sternocleidomastoid and receives venous drainage from the common facial vein (not shown), along with the superior and middle thyroid veins.

In addition to venous drainage of the neck, this highlights the sensory and motor components of the cervical plexus of nerves.

• The cervical plexus is formed by the anterior rami of cervical spinal nerves C1‒4. The sensory branches of the cervical plexus arise from the nerve point of the neck, just posterior to the midpoint of the sternocleidomastoid, and are visible on the donor’s right side. These sensory branches provide sensory innervation to the anterior and lateral neck as well as to the skin over the angle of the mandible.

• Three of the four sensory branches are visible (lesser occipital is not seen because it courses posterior to the external ear).

  • The great auricular nerve courses toward the ear in parallel with the external jugular vein.

  • The transverse cervical nerves course horizontally across the sternocleidomastoid to supply the anterior neck.

  • The supraclavicular nerves descend to the skin over the clavicle.

• The motor component of the cervical plexus is known as the ansa cervicalis (nerve loop of the neck) and supplies motor innervation to most of the infrahyoid muscles (thyrohyoid is innervated directly by C1, nerve to thyrohyoid).

  • The ansa cervicalis is formed by two roots, named by the spinal cord levels (C1‒3) contributing to them. The superior root of ansa cervicalis is formed by C1 spinal nerve fibers and descends vertically within the carotid sheath over the common carotid artery.

  • The superior root unites inferiorly with the inferior root of ansa cervicalis, formed by C2‒3, over the internal jugular vein. Motor branches emerge from the ansa cervicalis to supply the sternohyoid, omohyoid, and sternothyroid muscles.

The neck is compartmentalized vertically by fascial layers that facilitate visceral movements during swallowing and are clinically significant to the spread of infection.

The superficial fascia is a zone of loose connective tissue between the dermis and cervical deep fascia and is joined to both. It contains the platysma muscle and a variable amount of fat.

Deep cervical fascia is organized into the investing or superficial fascia, middle or pretracheal fascia, prevertebral fascia, and carotid sheath.

The investing fascia is shown in red and surrounds the entire neck like a collar. It splits around the trapezius and sternocleidomastoid muscles on each side. Inferiorly and anteriorly, the investing fascia remains as two layers after it has surrounded the sternocleidomastoid; where these layers are attached to the manubrium of the sternum, they create the suprasternal space (of Burns). More laterally, the investing fascia forms the roof of the posterior triangle of the neck, and posteriorly it blends with the nuchal ligament.

The middle (pretracheal) layer of fascia is subdivided into a muscular or infrahyoid layer (in purple ) and a visceral layer (in blue ). The muscular layer invests the infrahyoid muscles. The visceral layer surrounds the thyroid gland, larynx, trachea, and esophagus, providing fascial sheaths of varying thickness; it is incomplete posteriorly.

The prevertebral fascia (in orange ) forms a sleeve around the vertebral column and its associated muscles (longus colli, scalenes, levator scapulae, and deep back muscles). The alar fascia lies anterior to the prevertebral fascia, from which it is separated by loose connective tissue (the “danger space”). Note in the lower image that the true retropharyngeal space ends variably in the upper thorax between the first (T1) and seventh (T7) thoracic vertebrae, whereas the danger space extends inferiorly into the mediastinum, providing a path for infection (e.g., from retropharyngeal abscess) to enter the chest.

The carotid sheath is a composite fascial tube extending from the skull base into the thorax. It encloses the common and internal carotid arteries, internal jugular vein, and vagus nerve.

This plate highlights the anatomy of the fasciae of the head and neck, including the deep cervical, pretracheal, and prevertebral layers. These fascial layers are clinically important because they serve as surgical cleavage planes. Cervical fasciae can serve to limit the spread of infection or cancer in many cases, but also can allow head and neck infections to spread into the mediastinum.

Note that the sternocleidomastoid muscle (SCM) has been resected; identify its proximal and distal cut ends and the middle segment, reflected posteriorly.

Begin your study of this plate with the superficial layer of the deep cervical fascia (SLDCF), shown in pink, which invests the SCM and trapezius muscle. Note how the deep cervical fascia ensheathes the SCM and forms the roof of the posterior cervical triangle. The floor of the posterior triangle is the prevertebral fascia, shown in orange.

Note that as the deep cervical fascia splits to ensheathe the sternal head of SCM, its anterior and posterior layers attach to the manubrium of the sternum to create the suprasternal space (of Burns).

Superiorly, the deep cervical fascia encloses the submandibular and parotid salivary glands, contributing to their fibrous capsules.

Note the anterior subdivision of the prevertebral fascia, the alar fascia, which helps to seal the retropharyngeal space posteriorly. Anteriorly, the retropharyngeal space is bounded by the buccopharyngeal fascia ( green ), which blends posteriorly with the pretracheal fascia ( blue ).

The pretracheal fascia has two components, visceral and muscular.

• The blue visceral layer invests the thyroid gland, trachea, larynx, and esophagus. It is continuous posteriorly and superiorly with the buccopharyngeal fascia of the pharynx.

• The purple muscular layer invests the infrahyoid, or strap, muscles.

The carotid sheath is a composite fascial layer surrounding the internal jugular vein, common carotid artery, and vagus nerve. It is formed by the fusion of prevertebral, visceral pretracheal, and deep cervical fasciae.

The sternocleidomastoid muscles have been reflected bilaterally to better demonstrate the muscles of the anterior cervical triangle.

The hyoid bone is a key landmark in the neck. Its movement is coordinated with swallowing.

The muscles attached to the superior aspect of the hyoid bone are the suprahyoid muscles.

• The digastric muscle has an anterior belly attached to the digastric fossa on the deep surface of the body of the mandible and a posterior belly attached to the mastoid notch of the temporal bone. The two bellies are separated by an intermediate tendon that is tethered to the hyoid bone by a connective tissue pulley. The anterior belly is innervated by the nerve to mylohyoid muscle (CN V ₃ ); the posterior belly is innervated by the facial nerve (CN VII).

• The mylohyoid muscle is attached to the body of the hyoid bone and the mylohyoid line on the deep surface of the body of the mandible. It is innervated by the nerve to mylohyoid (CN V ₃ ).

• The stylohyoid muscle extends from the styloid process of the temporal bone to the body of the hyoid bone and is innervated by the facial nerve (CN VII).

The four muscles attached to the inferior aspect of the hyoid bone are collectively called the infrahyoid muscles.

• The superior bellies of the omohyoid and sternohyoid are superficial; the sternothyroid and thyrohyoid are deeper. All these muscles are innervated by the ansa cervicalis of the cervical plexus, except the thyrohyoid, which is innervated directly by C1 via the nerve to the thyrohyoid, which travels with the hypoglossal nerve.

• The omohyoid extends from the lateral and inferior border of the hyoid bone to the scapula, just medial to the scapular notch. It is a two-bellied muscle (thus its name) and has an intermediate tendon that is attached to the clavicle via a fascial sling. Note the close anatomical relationship of the intermediate tendon to the internal jugular vein.

• The sternohyoid extends from the manubrium of the sternum to the body of the hyoid bone.

• The sternothyroid extends from the manubrium to the oblique line on the thyroid cartilage.

• The thyrohyoid extends from the oblique line on the thyroid cartilage to the body of the hyoid bone.

Note that several midline structures are visible medial to the infrahyoid muscles, including the thyrohyoid membrane, thyroid cartilage, cricothyroid ligament, cricoid cartilage, thyroid gland, and trachea.

On this lateral view of the neck, first identify the sternocleidomastoid muscle, which delineates the anterior and posterior cervical triangles.

• Note that the sternocleidomastoid extends from the mastoid process of the temporal bone to the manubrium of the sternum (sternal head) and the clavicle (clavicular head). It is innervated by the accessory nerve (CN XI).

The anterior triangle is bounded by the anterior border of the sternocleidomastoid, inferior border of the mandible, and midline of the neck.

• Note the suprahyoid muscles (anterior and posterior bellies of digastric, mylohyoid, and stylohyoid) and the infrahyoid muscles (sternohyoid, superior belly of omohyoid, sternothyroid, and thyrohyoid).

• The stylohyoid typically splits around the intermediate tendon of the digastric muscle before it attaches to the hyoid bone.

• The anterior triangle can be subdivided into the submental, submandibular, carotid, and muscular triangles. The boundaries of each of these smaller triangles, other than those of the submental triangle, are clearly visible.

  • The submental triangle is formed by the anterior bellies of the digastric muscles and the hyoid bone.

  • The submandibular triangle is formed between the anterior and posterior bellies of the digastric muscle and the inferior border of the mandible.

  • The carotid triangle is bounded by the superior belly of the omohyoid, posterior belly of digastric, and upper part of anterior border of sternocleidomastoid.

  • The muscular triangle is bounded by the superior belly of the omohyoid, lower part of anterior border of sternocleidomastoid, and midline of neck.

The posterior triangle is bounded by the posterior border of the sternocleidomastoid, anterior border of trapezius, and middle third of clavicle.

• The inferior belly of the omohyoid subdivides the posterior triangle into an occipital triangle superiorly and a supraclavicular triangle inferiorly.

• The floor of the posterior triangle is formed by the prevertebral fascia overlying the splenius capitis, levator scapulae, and middle and posterior scalene muscles.

• The anterior scalene is partially visible in this view, separated from the middle scalene muscle by the trunks of the brachial plexus.

Demonstrates the prevertebral musculature responsible for flexion of the head and the neck. Superficial muscles, viscera, and deep fasciae of the neck have been removed to expose the prevertebral muscles. A coronal section through the skull at the level of the basiocciput allows visualization of the most superior group of prevertebral muscles (rectus capitis anterior and rectus capitis lateralis). The muscles illustrated are all innervated by anterior rami of the cervical spinal nerves.

• The rectus capitis anterior extends from the base of the skull, anterior to the occipital condyle, to the lateral mass of C1.

• The rectus capitis lateralis extends from the jugular process of the occipital bone to the transverse process of C1.

The longus capitis spans from the basilar part of the occipital bone to the anterior tubercles of the transverse processes of C3‒6.

The longus colli is a complex muscle. It has superior and inferior oblique parts and a vertical middle part that collectively span from C1 to T3. Its upper fibers run between the anterior tubercles of the transverse processes of C3‒5 and the anterior tubercle of C1; central fibers run between the anterior surface of the bodies of C5‒T3 and the anterior surface of the bodies of C2‒4; lower fibers run between the anterior surface of the bodies of T1‒3 and the anterior tubercles of the transverse processes of C5 and C6.

• The anterior scalene extends from the transverse processes of C3‒6 to the scalene tubercle of the first rib. Note the phrenic nerve as it courses anterior to the anterior scalene muscle.

• The middle scalene spans from the posterior tubercles of the transverse processes of the lower five cervical vertebrae to the first rib.

• The posterior scalene spans from the posterior tubercles of the transverse processes of C4‒6 to the second rib.

• Note the trunks of the brachial plexus and the subclavian artery passing between the anterior and middle scalene muscles.

The upper image has the sternocleidomastoid muscle intact and well demonstrates the sensory branches of the cervical plexus.

• Note the presence of the external jugular vein on the superficial surface of the sternocleidomastoid, as it is formed by the union of the posterior branch of the retromandibular vein and the posterior auricular vein just inferior to the angle of the mandible.

In the posterior triangle, note the emergence of the four sensory branches of the cervical plexus at an area termed the nerve point of the neck.

• The great auricular nerve courses superiorly in parallel with the external jugular vein to supply the skin over the angle of the mandible and around the external ear.

• The lesser occipital nerve courses along the posterior border of the sternocleidomastoid to supply the skin of the scalp behind the ear.

• The transverse cervical nerve travels horizontally over the sternocleidomastoid and medially to supply the skin of the anterior neck.

• The supraclavicular nerves descend to the skin over the clavicle.

Also note the presence of the accessory nerve (CN XI) in the posterior cervical triangle, descending on the superficial surface of levator scapulae to reach and innervate the trapezius muscle posteriorly.

The lower figure has the sternocleidomastoid muscle reflected, and the neurovascular elements of the anterior triangle are more readily visible.

• Note the close relationship of the common carotid artery and internal jugular vein, with the vagus nerve sandwiched between them posteriorly. The common carotid artery, internal jugular vein, and vagus nerve are enclosed in life by a connective tissue carotid sheath that has been removed in this image.

• Superficial to the carotid sheath and its contents, note the ansa cervicalis, the motor component of the cervical plexus, responsible for supplying innervation to most of the infrahyoid muscles.

• The superior root of ansa cervicalis is formed by C1 fibers (thus its name) and is located anteriorly over the carotid arterial system. Tracing the superior root upward, note that it is contiguous with the hypoglossal nerve and then descends on the carotid sheath; thus it is sometimes termed the descendens hypoglossi, or descending hypoglossal nerve.

• The inferior root is formed by C2‒3 fibers and is positioned more posteriorly over the internal jugular vein. You can see the convergence of C2 and C3 forming the inferior root in this image.

With the sternocleidomastoid reflected, the neurovascular elements of the posterior triangle are also more readily visible.

• The phrenic nerve is visible descending on the superficial surface of the anterior scalene muscle, with branches of the thyrocervical arterial trunk passing over it.

• Roots of the brachial plexus are seen clearly emerging between the anterior and middle scalene muscles.

• Note the relationship of the accessory nerve (CN XI) on the superficial surface of levator scapulae muscle. The accessory nerve receives some sensory contributions from the upper cervical spinal nerves.

The upper image shows the relationship of the cervical plexus with the hypoglossal and spinal accessory cranial nerves.

The cervical plexus is formed by the anterior rami of C1‒4 spinal nerves. These fibers can carry sensory, motor, and postganglionic sympathetic fibers. The sympathetics (which originate from neurons within superior cervical ganglion) join the nerves by way of gray rami communicantes at the sites marked “S” on this image.

Fibers from the C1 spinal nerve course anteriorly, to form either the nerve to thyrohyoid (which also supplies a suprahyoid muscle known as the geniohyoid ) or the superior root of ansa cervicalis. The superior root is named as such because of its origin from C1 fibers.

The inferior root of ansa cervicalis is formed by C2 and C3 fibers that unite and descend to join with the superior root to complete the loop. Motor branches from this loop extend to innervate most infrahyoid muscles, including sternohyoid, sternothyroid, and omohyoid.

The sensory branches of the cervical plexus carry sensory and sympathetic fibers and arise from C2‒4 spinal nerves. The lesser occipital nerve is from C2‒3, the great auricular and transverse cervical nerves receive input from C2‒3, and the supraclavicular nerves are from C3‒4.

The phrenic nerve is sometimes included as a component of the cervical plexus because it is formed largely by the anterior ramus of C4, with contributions from C3 and C5 as well. It provides motor and sensory innervation to the diaphragm muscle.

The lower figure demonstrates structures in the root of the neck, from an anterior view. The root of the neck is the junction between the neck and thorax and is bounded by the superior thoracic aperture, formed by the manubrium of the sternum, first ribs, and T1 vertebral bodies.

For orientation purposes, note the trachea in midline and the thyroid gland that has been retracted on the right side. The internal jugular vein and common carotid artery on the right side have been resected to reveal deeper structures in the root of the neck.

The brachiocephalic trunk is a branch from the aortic arch and gives rise to the common carotid and subclavian arteries.

The subclavian artery is divided into three segments, based on its anatomical relationship to the anterior scalene muscle, with the first segment being medial, the second posterior (to the anterior scalene), and the third lateral.

• The first segment of the subclavian artery gives rise to the vertebral artery, thyrocervical trunk, and internal thoracic artery (not visible in this image).

  • The vertebral artery ascends to enter usually the transverse foramen of C6.

  • The thyrocervical trunk gives rise to several branches, including the inferior thyroid, ascending cervical, transverse cervical, and suprascapular arteries.

  • The inferior thyroid artery supplies the lower pole of the thyroid gland along with the parathyroid glands.

  • The ascending cervical artery provides muscular branches to deep cervical muscles and into the intervertebral foramina to supply nerve roots as well.

  • The transverse cervical artery supplies the trapezius muscle.

  • The suprascapular artery travels posteriorly to the scapula to supply the supraspinatus and infraspinatus muscles.

• The second segment of the subclavian artery gives rise to the costocervical trunk, which divides into a superior intercostal and deep cervical artery.

• The third segment of the subclavian artery often gives rise to the dorsal scapular artery, which vascularizes the rhomboid and levator scapulae muscles. The dorsal scapular artery may alternatively arise from the transverse cervical artery.

Note the subclavian vein coursing anterior to the anterior scalene muscle, whereas the subclavian artery travels posterior to it.

Many important nerves course vertically through the root of the neck.

• Starting laterally, recall that the roots of the brachial plexus emerge between the anterior and middle scalene muscles.

• The phrenic nerve courses anterior to the anterior scalene muscle, but posterior to the lateral branches of the thyrocervical trunk (transverse cervical and suprascapular arteries).

• Medial to the phrenic nerve, the vagus nerve courses in the posterior aspect of the carotid sheath, between the internal jugular vein and common carotid artery.

• The right vagus nerve passes anterior to the first segment of the subclavian artery on the right side. The vagus nerve gives rise to the right recurrent laryngeal nerve, which loops under the subclavian artery and ascends medially in the groove between the trachea and esophagus.

The sympathetic trunk descends through the neck on the anterior surface of the anterior scalene muscle. The cervical sympathetic trunk receives no white rami and exhibits three ganglia, including the middle cervical ganglion visible on this image; it is located at the level of the cricoid cartilage and just superior to the inferior thyroid artery.

The common carotid arteries ascend in the neck until they reach the level of the thyroid cartilage, where they divide into internal and external carotid arteries.

The internal carotid artery is the more posterior of the two branches and ascends without branching in the neck until it reaches the carotid canal at the skull base.

The external carotid artery vascularizes structures in the superficial head, scalp, and neck with eight branches that can be remembered by the mnemonic “Some little fat man stole papa’s only apple,” with the first letter of each word representing a branch of the external carotid, starting with superior thyroid artery.

The superior thyroid artery is the first branch from the external carotid artery and descends to supply neighboring muscles and the superior part of the thyroid gland. It gives rise to the superior laryngeal artery, which accompanies the internal branch of the superior laryngeal nerve of the vagus nerve as it pierces the thyrohyoid membrane to supply the superior laryngeal mucosa.

The lingual artery is the second branch of the external carotid artery and travels anteriorly toward the floor of the oral cavity to supply blood to the tongue and floor of the mouth. It passes deep to the hypoglossal nerve, stylohyoid, and posterior belly of the digastric as it approaches the hyoglossus muscle.

The facial artery is the third branch of the external carotid artery. It travels deep to the posterior belly of the digastric and stylohyoid, then courses under the angle of the mandible and deep to the submandibular gland. It supplies the submandibular gland before entering the face.

The external carotid runs posterior to the neck of the mandible and through the parotid gland as it gives rise to its two terminal branches, the maxillary and superficial temporal arteries.

The maxillary artery is the fourth branch of the external carotid artery, supplying structures in the deep head.

The superficial temporal artery, the fifth branch, travels through the parotid gland and gives rise to the transverse facial branch as it emerges onto the face and temporal fossa to supply the face and scalp.

The posterior auricular artery is the sixth branch of the external carotid artery and travels posteriorly between the external acoustic meatus and the mastoid process to reach the scalp.

The occipital artery is the seventh branch and also courses posteriorly to reach the scalp. It travels superficial to the hypoglossal nerve, crossing it in a characteristic manner at the level of the mandibular angle.

The eighth branch of the external carotid is the ascending pharyngeal artery. It branches medially from the external carotid artery, traveling superiorly to supply deep structures in the head and neck.

This plate demonstrates the bony and cartilaginous framework of the external nose.

The upper image demonstrates the anterolateral view of the external nose as it is formed by bone, cartilage, and fibrofatty connective tissue.

• The paired nasal bones, frontal processes of the maxillary bones, and frontal bone contribute to the root of the nose. The nasal bones and maxillae enclose the two piriform apertures, or anterior openings into the nasal cavities.

• Several cartilages complete the external nose anteriorly, including two lateral and two alar cartilages, along with the unpaired septal cartilage. Fibrofatty tissue completes the lateral sides of each ala of the nose.

The lower image demonstrates the inferior view of the external nose, with the anterior tip of the nose at the top of the image. Note the anterior nares or openings of the nasal cavity, bounded by both the alar cartilages and fibrofatty tissues. The septal nasal cartilage attaches the external nose to the facial skeleton at the intermaxillary suture.

This plate demonstrates key anatomical relationships between the muscles, nerves, and arteries of the face.

The muscles of facial expression lie in the subcutaneous tissue of the face, moving the skin of the face to demonstrate mood.

• In the frontal region, the frontalis muscles serve to elevate the eyebrows and create horizontal wrinkles across the forehead. Blending with each frontalis muscle is a procerus muscle, a small triangular muscle of facial expression that lies over the glabella, between the eyebrows. Just lateral to the procerus, identify the corrugator supercilii muscle, which has muscle fibers that run horizontally along the medial supraorbital margin.

• Associated with the nasal region, note the nasalis muscle, which includes a transverse part and an alar part that are responsible for flaring the nostrils. On either side of the nasal septum, note the depressor septi nasi muscles. These muscle fibers blend with the orbicularis oris muscle in the oral region below.

The blood supply to the face consists of branches from both the internal and external carotid arteries.

• The internal carotid artery gives rise to the ophthalmic artery, which branches to form the supratrochlear and supraorbital arteries supplying the frontal region, as well as the dorsal nasal and external nasal arteries supplying the nasal region. The dorsal nasal artery supplies the more superior dorsum of the nose, and the external nasal artery supplies the more inferior region of the dorsum of the nose.

• The external carotid artery gives rise to several branches that supply various regions of the face. First, the superficial temporal artery is a terminal branch of the external carotid artery. The transverse facial artery is given off from the superficial temporal artery before it leaves the parotid gland. The infraorbital artery is a branch of the maxillary artery, the other terminal branch of the external carotid artery. The facial artery is yet another branch of the external carotid artery; this vessel crosses the mandible and gives rise to an inferior labial branch and a superior labial branch. The lateral nasal artery branches from the facial artery as it passes the nose and supplies the dorsum and ala. After the facial artery passes superior to the ala of the nose, it is renamed the angular artery.

The sensory innervation from the skin of the face is mediated by branches of the trigeminal nerve.

The ophthalmic division of the trigeminal nerve gives rise to the frontal nerve in the orbit, which branches to form the supratrochlear and supraorbital nerves that supply the frontal region. The ophthalmic nerve also gives rise to the nasociliary nerve in the orbit, which in turn branches to form the external nasal branch of the anterior ethmoidal nerve. The infratrochlear nerve is the other terminal branch of the nasociliary nerve (along with the anterior ethmoidal nerve). It supplies the root of the external nose.

The maxillary division of the trigeminal nerve gives rise to the infraorbital nerve, which supplies the midface.

The upper image is a sagittal section through the head with the midline nasal septum removed. The middle image is a speculum view of the nasal cavity through the external nares. The lower image is a sagittal section through the head with the nasal septum removed and the nasal conchae cut back to their roots.

When considering the internal anatomy of the nasal cavity, it is useful to begin anteriorly with the nasal vestibule. This area of the nasal cavity is lined by skin, rather than by respiratory epithelium as is the rest of the nasal cavity. The delineation between these different histological linings is termed the limen nasi, visible on the upper image.

The lateral wall of each nasal cavity is characterized by scroll-shaped conchae (turbinates), covered by respiratory epithelium. Typically, three conchae are present: superior, middle, and inferior. Each concha has a slit-like space inferior to it known as a meatus ; each meatus is named for the concha superior to it. The space above the superior concha is termed the sphenoethmoidal recess.

The sphenoethmoidal recess and the meatal spaces receive secretions from other structures, such as paranasal air sinuses or lacrimal gland. Paranasal air sinuses developmentally grow out of the nasal cavity during embryonic development and into surrounding bones. They include the frontal, maxillary, sphenoid, and ethmoidal sinuses, each of which drains into a specific area of the nasal cavity.

• The sphenoid sinus drains to the sphenoethmoidal recess.

• The posterior ethmoidal air cells (sinuses) drain to the superior meatus.

• The frontal sinus, maxillary sinus, and anterior and middle ethmoidal air cells (sinuses) drain into the middle meatus either directly (middle ethmoidal air cells) or indirectly through the hiatus semilunaris (visible on lower image).

• The middle ethmoidal air cells drain onto a bubble-like structure in the middle meatus known as the ethmoidal bulla. The nasolacrimal duct drains to the inferior meatus.

At the posterior border of each nasal cavity, there is an opening leading to the nasopharynx known as the choana.

• The nasopharynx, or most superior part of the pharynx, extends from the skull base to the uvula of the soft palate. It contains several clinically important structures, including the lymphoid pharyngeal tonsil on the roof of the nasopharynx and the opening of the pharyngotympanic (auditory, eustachian) tube.

• The pharyngotympanic tube has several specializations surrounding it, including a C-shaped cartilaginous formation superior to it, known as the torus tubarius.

Shows the bony anatomy of the lateral wall of each nasal cavity, with the conchae intact in the upper image and resected in the lower image, to demonstrate key openings located deep in the lateral nasal wall.

Several bones contribute to the lateral nasal wall, including the nasal, frontal, and maxillary, and lacrimal bones anteriorly.

Note the frontal sinus in the frontal bone, which drains to the hiatus semilunaris by way of a soft tissue frontonasal duct.

The ethmoid bone forms the roof of the nasal cavity, with a cribriform plate to transmit cranial nerve I, as well as the superior and middle conchae. Occasionally, a highest (or supreme) concha is present above the superior conchae and is also part of the ethmoid bone.

Note that the inferior concha is its own bone; it is not part of the ethmoid.

Posteriorly, the sphenoid and palatine bones help to complete the roof, lateral wall, and floor of the nasal cavity.

Several openings can be seen in relation to the nasal cavity, including the sphenopalatine foramen and incisive canal.

• The sphenopalatine foramen is an opening from the nasal cavity into the more lateral pterygopalatine fossa and serves as a passageway for neurovasculature to access the nasal cavity.

• The incisive canal is located anteriorly in the floor of the nasal cavity to transmit the nasopalatine nerve from the nasal septum to the anterior hard palate.

In addition, the openings for drainage of the paranasal air sinuses can be visualized in the lower image.

• The sphenoid sinus drains to the space above the superior conchae, the sphenoethmoidal recess.

• The posterior ethmoidal air cells drain to the superior meatus.

• The anterior ethmoidal air cells drain to the semilunar hiatus, along with the frontonasal duct and the maxillary sinus. The semilunar hiatus is bounded anteriorly by a bony ethmoidal projection known as the uncinate process because of its hook-like appearance.

• The middle ethmoidal air cells drain onto the ethmoidal bulla, which is housed in the middle meatus, along with the hiatus semilunaris.

• Finally, the nasolacrimal canal drains to the inferior meatus under the inferior concha.

Focuses on the medial wall of each nasal cavity (nasal septum).

The nasal septum is a composite structure formed by two bones (perpendicular plate of ethmoid and vomer) along with nasal septal cartilage anteriorly.

The septum is anchored to the floor of the nasal cavity through its attachment to the anterior nasal spine and nasal crest of the maxilla, as well as the nasal crest of the palatine bone.

The vomer articulates with the sphenoid bone superoposteriorly. Note the groove formed by the nasopalatine nerve and vessels on the vomer; this nerve is a branch of cranial nerve V ₂ that supplies the septum and then exits the nasal cavity by way of the incisive canal to reach the anterior hard palate.

The vomer is the part of the nasal septum responsible for dividing the posterior opening between the nasal cavity and the nasopharynx into two openings (choanae).

The nasal cavity receives innervation from several cranial nerves, including CN I (olfactory nerve), CN V ₁ (ophthalmic division of trigeminal nerve), and CN V ₂ (maxillary division of trigeminal nerve).

The two upper images represent the territory of the peripheral processes of the olfactory nerve on the lateral nasal wall and nasal septum. Recall that the olfactory nerve exits the nasal cavity by way of the cribriform plate of the ethmoid bone in the roof of the nasal cavity.

The middle and lower images show the actual nerve distribution for CNs I, V ₁ , and V ₂ . You can see that the olfactory nerve (CN I) has its peripheral processes in the upper lateral wall and in the upper nasal septum.

• The cell bodies for CN I are housed in the olfactory epithelium in the roof of the nasal cavity.

• The central processes of CN I travel through the cribriform plate of the ethmoid and synapse in the olfactory bulb in the anterior cranial fossa.

• Recall that CN I conveys the special sense of smell, not somatic sensation (pain, temperature, and touch). CN V conveys somatic sensation from the nasal cavity as well as from other adult derivatives of the first pharyngeal arch.

In the middle and lower images, you can see that the anterior ethmoidal nerve of the ophthalmic division of the trigeminal nerve (CN V ₁ ) supplies the anterior mucosa of the lateral nasal wall and nasal septum through medial and lateral internal nasal branches.

In the middle image, the perpendicular plate of the palatine bone has been removed in part to show the pterygopalatine fossa, with CN V ₂ , pterygopalatine ganglion, and branches of V ₂ emerging from the ganglion.

• These branches are the pharyngeal branch, greater and lesser palatine nerves, posterior lateral nasal branches to the conchae, and nasopalatine nerve, which courses along the nasal septum, deep to the mucosa.

• The nerve of the pterygoid canal travels through the sphenoid bone to reach the pterygopalatine ganglion. This nerve carries preganglionic parasympathetic fibers from the greater petrosal nerve of CN VII that synapse in the pterygopalatine ganglion, along with postganglionic sympathetic fibers from the deep petrosal nerve from the carotid plexus.

In the lower image, note that sensory innervation of the nasal septum is provided by CN I (smell) and by the anterior ethmoidal nerve of CN V ₁ , nasopalatine, and infraorbital nerves of CN V ₂ for general sensation.

This plate demonstrates the arterial supply and venous drainage of the nasal cavity. The two upper images show the arterial supply and the two lower images the venous drainage.

The upper left image is a parasagittal section through the nasal cavity showing the lateral nasal wall, with the conchae visible. The lateral wall of the nasal cavity receives its arterial blood supply from the external carotid artery (and two of its branches, the maxillary and facial arteries) and the internal carotid artery (and one of its branches, the ophthalmic artery).

The maxillary artery, one of the terminal branches of the external carotid artery, gives rise to the sphenopalatine artery. The sphenopalatine artery gives off the posterior lateral nasal artery, which supplies much of the posterolateral nasal wall.

The facial artery, a branch of the external carotid artery, vascularizes the nasal vestibule via its lateral nasal branch and its alar branches.

The ophthalmic artery gives rise to anterior ethmoidal arteries, which supply the superior and anterior aspects of the lateral nasal wall.

The upper right image is a midsagittal section through the nasal cavity showing the nasal septum. The nasal septum receives its arterial blood supply from the external carotid artery (maxillary and facial arteries) and the internal carotid artery (ophthalmic artery). These arteries anastomose to form the Kiesselbach’s plexus. This plexus is formed by five arteries, including the anterior and posterior ethmoidal arteries, sphenopalatine artery, greater palatine artery, and superior labial artery. It is the most common site of epistaxis (nasal bleeding).

The lower images demonstrate the venous drainage of the nasal cavity via the sphenopalatine, facial, and ophthalmic veins. Blood from the sphenopalatine veins drains back to the pterygoid venous plexus, which branches from the maxillary vein. Blood from the ethmoidal veins tracks back through the ophthalmic veins to the cavernous sinus in the cranial cavity.

Uniquely demonstrates the innervation of both the lateral nasal wall and the nasal septum by detaching and reflecting the nasal septum superiorly, creating a hinge where the septum attaches to the roof of the nasal cavity.

In addition, the pterygopalatine fossa has been exposed in this plate, through the removal of the perpendicular plate of the palatine bone. Note the pterygopalatine ganglion at the superior end of the pterygopalatine fossa.

The peripheral processes of cranial nerve (CN) I, the olfactory nerve, are visible superiorly in this plate, associated with both the lateral nasal wall and the nasal septum.

The main source of general sensation to the nasal cavity is the trigeminal nerve, specifically CNs V ₁ and V ₂ .

The anterior ethmoidal nerve of CN V ₁ gives rise to external nasal branches that supply the anterior nasal cavity, while the internal nasal branches of the infraorbital nerve of CN V ₂ supply the vestibule.

The maxillary division of CN V gives rise to several branches in the pterygopalatine fossa, including the nasopalatine nerve, greater and lesser palatine nerves, and posterior lateral nasal branches. The maxillary division gives rise to sensory nerves that course through the pterygopalatine ganglion without synapsing. These sensory nerves pick up sympathetic and parasympathetic fibers in the ganglion that will supply mucosal glands in these nerves’ targets.

The nasopalatine nerve arises in the pterygopalatine fossa and enters the nasal cavity via the sphenopalatine foramen. It then courses along the vomer of the nasal septum, providing general sensation to the septal mucosa. Inferiorly, the nasopalatine nerve travels through the incisive canal to reach and innervate the anterior mucosa of the hard palate.

The posterior lateral nasal branches of CN V ₂ supply the mucosa over the nasal conchae on the lateral nasal wall.

The greater and lesser palatine nerves are visible coursing inferiorly in the pterygopalatine fossa, descending from the pterygopalatine ganglion toward the hard palate. The greater palatine nerve supplies the hard palatal mucosa posterior to the canines, whereas the lesser palatine nerve supplies the soft palatal mucosa. The nasopalatine nerve supplies the hard palatal mucosa anterior to the canine teeth.

The upper image is a parasagittal section through the head, demonstrating several of the paranasal sinuses and their drainage sites into the nasal cavity. Note that the middle concha has been resected to show the underlying structures, including the hiatus semilunaris.

Anteriorly, the frontal sinus is visible, with the frontonasal duct draining its secretions into the hiatus semilunaris in the middle meatus. The opening for the maxillary sinus in the hiatus semilunaris is also well demonstrated in this image.

The anterior-to-posterior extent of the ethmoid air cells (sinuses) is clearly shown in the upper image.

Posterior to the ethmoid air cells, note the large sphenoid sinus in the body of the sphenoid bone. The opening of the sphenoid sinus into the sphenoethmoidal recess is well shown in this sagittal section.

The lower image is a more lateral parasagittal section through the maxilla to demonstrate the maxillary sinus and its relationship to the roots of the maxillary teeth. Also note the superiorly placed drainage site for the maxillary sinus into the nasal cavity on the sinus’ medial wall.

The paranasal sinuses developmentally arise from the nasal cavity, so that in the mature state, they drain their secretions into it.

About the seventh month of gestational development, three medial projections develop on the lateral wall of the nose: the agger nasi, maxilloturbinate, and ethmoidoturbinate. The agger nasi forms the anterior floor of the frontal sinus. The maxilloturbinate forms the inferior conchae and maxillary sinus. The ethmoidoturbinate forms the superior and middle conchae, the ethmoidal cells.

The maxillary sinus is the first paranasal sinus to develop. Its growth is characterized by a biphasic pattern, with the early phase of pneumatization occurring horizontally and posteriorly and the later phase occurring inferiorly toward the maxillary teeth.

By contrast, the frontal sinus is the last of the paranasal sinuses to pneumatize. Pneumatization begins by 2 years after birth. Growth continues throughout childhood, and full size is achieved well after puberty.

The nasolacrimal duct drains the lacrimal sac and runs from the lacrimal fossa over the maxilla to empty into the inferior meatus.

The ethmoidal cells are present at birth and continue to grow until puberty. The middle concha divides the ethmoid sinuses into anterior, middle, and posterior groups of cells, all with different drainage patterns to the nasal cavity. Pneumatization progresses anterior to posterior.

The sphenoid sinus is formed by the posterior ethmoidal cells growing into the sphenoid bone at 2 years postnatally, and development continues into puberty.

The upper image is a coronal section through the head at the level of the nasal cavity. Three of the four paranasal air sinuses are visible, including the frontal, ethmoidal, and maxillary sinuses. The sphenoid sinuses are posterior to the coronal section in the upper image and are visible in the lower image.

In the upper image, the frontal lobes of the cerebral cortex are visible and separated by the dural fold known as the falx cerebri. At the inferior pole of the frontal lobes, note the olfactory bulbs, where central processes of cranial nerve (CN) I synapse.

Just lateral to the olfactory bulbs, note the bilateral spaces within the frontal bone, the frontal sinuses.

Inferior to the frontal sinuses and medial to each orbit, you can see the ethmoid sinus (ethmoid air cells). The ethmoid sinus has anterior-to-posterior depth, as represented in the lower image, a horizontal (transverse) section through the head at the level of the nose. Note that posterior to the ethmoid sinus, the sphenoid sinuses are present.

The nasal cavity is shown, divided into two parts by the midline nasal septum. The lateral nasal walls are characterized by nasal conchae, with the middle and inferior conchae visible in this coronal view. The floor of the nasal cavity is formed by the hard palate.

The maxillary sinuses are shown, draining into the nasal cavity superiorly at the middle meatus.

The oral cavity is separated from the nasal cavity superiorly by the hard palate, laterally by the buccinator muscle of facial expression, and inferiorly by the mylohyoid muscle.

The body of the tongue, formed largely by intrinsic muscles of the tongue, is prominent in the oral cavity, with the genioglossus muscle attaching to it from below. The geniohyoid bone is located just inferior to the genioglossus muscle, and the mylohyoid forms the floor of the mouth.

There are three pairs of major salivary glands: parotid, submandibular, and sublingual.

The parotid gland’s name defines its location, adjacent to ( para ) the external ear ( otid/ous ). Each gland has a superficial component that extends superficially over the masseter muscle and superiorly toward the zygomatic arch. It extends posteriorly to the mastoid process and attached sternocleidomastoid muscle. Medially, it projects toward the styloid process of the temporal bone.

• The parotid duct (Stensen’s duct) emerges anteriorly from the parotid gland and courses superficial to masseter en route to the buccinator muscle. The parotid duct pierces the buccinator muscle to drain into the oral cavity opposite the second maxillary molar tooth.

• The anterior and posterior divisions of the retromandibular vein pass through the parotid gland, along with the facial nerve after it exits the stylomastoid foramen.

• The parotid gland receives its parasympathetic secretomotor innervation from the glossopharyngeal nerve.

The submandibular gland is located along the body of the mandible, creating a submandibular fossa on the mandible’s deep surface.

• The submandibular gland is composed of a superficial portion, housed in the submandibular triangle, and a deep portion, located superior to mylohyoid and medial to hyoglossus muscles.

• The submandibular duct (or Wharton’s duct) passes superior to the lingual nerve (from CN V ₃ ). The duct courses anteriorly to drain onto the sublingual caruncle just lateral to the frenulum of the tongue.

• The submandibular gland receives its parasympathetic secretomotor innervation from the nervus intermedius derived from the facial nerve.

The sublingual gland lies in the floor of the oral cavity, deep to the mucosa.

• The sublingual gland drains by way of 10 to 15 ducts (of Rivinus) directly onto the floor of the mouth along the sublingual folds.

• The sublingual gland receives its parasympathetic secretomotor innervation from the facial nerve.

Demonstrates the course of the motor root of the facial nerve (CN VII) and its relationship to the parotid bed and parotid gland. Motor fibers of the facial nerve supply skeletal muscles that develop from the second pharyngeal arch, including muscles of facial expression (mimetic muscles), posterior belly of digastric, and stylohyoid.

The upper figure shows the motor root of the facial nerve as it emerges from the base of the skull at the stylomastoid foramen, located anterior to the mastoid process of the temporal bone and inferior to the external acoustic meatus.

The facial nerve immediately gives rise to the posterior auricular nerve and the nerves to the posterior belly of digastric and stylohyoid muscles. The posterior auricular nerve innervates the occipital belly of the occipitofrontalis muscle and some of the extrinsic and intrinsic auricular muscles. The small auricular muscles modify auricular shape minimally, if at all.

The facial nerve then enters the parotid gland, where it typically divides into temporofacial and cervicofacial trunks (see lower figure). The trunks divide further, forming a parotid plexus (pes anserinus) within the gland. Branching patterns vary considerably, but the temporofacial trunk usually gives rise to temporal, zygomatic, and buccal branches and the cervicofacial division to buccal, marginal mandibular, and cervical branches.

The upper image demonstrates the more superficial muscles of mastication (temporalis and masseter) as well as the muscles of facial expression associated with the upper and lower lips.

• The temporalis muscle lies superiorly in the temporal fossa and attaches inferiorly to the coronoid process of the mandible. It elevates the mandible, and its posterior fibers retract the mandible, or pull the jaw posteriorly. It is innervated by deep temporal nerves of cranial nerve (CN) V ₃ .

  • The temporalis muscle is invested by the deep temporal fascia. The superficial temporal fascia attaches to the superior temporal line superiorly and to the zygomatic arch inferiorly.

• The masseter muscle extends from the maxillary process of the zygoma and zygomatic arch to the angle and ramus of the mandible. It serves to elevate the mandible, and its superficial fibers act to protract the mandible, or pull the jaw anteriorly.

• Surrounding the mouth, note the orbicularis oris, a muscle of facial expression responsible for closing the mouth.

• Related to the upper lip, note the following muscles of facial expression from medial to lateral: levator labii superioris alaeque nasi, levator labii superioris, and zygomaticus minor, when present. These muscles acts to elevate the upper lip.

• Related to the angle of the mouth, note the buccinator, levator anguli oris, zygomaticus major, and depressor anguli oris muscles. The buccinator acts to hold the cheek against the teeth to prevent food from entering the oral vestibule. Note that the parotid duct pierces buccinator muscle to access the oral cavity. The levator anguli oris and zygomaticus major muscles elevate the angle of the mouth, whereas the depressor anguli oris depresses it.

• Related to the lower lip, note the depressor labii inferioris and mentalis muscles. The depressor labii inferioris depresses the lower lip, whereas the mentalis protrudes the lower lip.

The lower image has much of the masseter muscle removed, to demonstrate the attachment of temporalis muscle to the coronoid process of the mandible.

• In this view the mandibular notch is visible. Through this notch, the neurovascular supply to the masseter can be identified: masseteric nerve of CN V ₃ and masseteric artery of maxillary artery.

• In addition, through the mandibular notch, the lateral pterygoid (a deeper muscle of mastication) can be observed.

The upper image continues to remove superficial structures to reveal deeper muscles of mastication. The medial portion of the mandibular ramus has been resected, along with the coronoid process of the mandible. This view reveals a complete view of the lateral and medial pterygoid muscles. The naming of these muscles refers to the side of the lateral pterygoid plate to which they attach.

• The lateral pterygoid muscle is organized into two heads, superior and inferior.

  • Proximally, the lateral pterygoid muscle attaches to the lateral surface of the lateral pterygoid plate and the greater wing of the sphenoid bone.

  • The superior head attaches distally to the joint capsule and articular disc of the temporomandibular joint (TMJ), while the inferior head attaches to the pterygoid fovea on the neck of mandible.

  • The lateral pterygoid muscle depresses and protracts the mandible.

• The medial pterygoid muscle originates proximally from the medial surface of the lateral pterygoid plate and the maxillary tuberosity. It attaches distally to the ramus of mandible.

  • The medial pterygoid forms a functional sling around the mandibular ramus along with the masseter muscle. Both function to elevate and protrude the mandible.

The lower image represents a posterior view of the infratemporal fossa and its muscular and neurovascular contents; this coronal section is through the skull just posterior to the TMJ. The carotid canal is visible in the temporal bone superiorly, with the internal carotid artery taking a horizontal course at this level.

• The nasopharynx is visible from this view, with the cartilaginous parts of the pharyngotympanic tube opening into the nasopharynx on each side. The choanae, or internal nares, are the doorways connecting the nasopharynx with the nasal cavity anteriorly.

• Laterally, the relationship between the lateral and medial pterygoid muscles is clarified.

  • The horizontally oriented lateral pterygoid pulls the TMJ forward to allow for depression and protraction of the mandible.

  • The more vertically oriented medial pterygoid pulls the mandible superiorly to elevate it.

  • Note that both pterygoids angle medially so that on contraction, these muscles contribute to contralateral excursion, or movement to the opposite side.

• Laterally, the relationship among the neurovascular elements of the infratemporal fossa is clarified.

  • Note the position of the sphenomandibular ligament, an extrinsic ligament of the TMJ that extends from the spine of the sphenoid bone to the lingula of the mandible. Most of the neurovascular elements are located superficial and anterior to the sphenomandibular ligament.

  • The root of cranial nerve (CN) V ₃ exits the skull base to enter the infratemporal fossa at the foramen ovale. At this level, CN V ₃ is closely associated with the otic ganglion, which is attached to its medial surface; the parasympathetic otic ganglion is associated with CN IX and provides postsynaptic innervation to the parotid gland.

  • CN V ₃ quickly divides into anterior and posterior divisions. The smaller anterior division provides motor branches to muscles of mastication and the long buccal nerve. The larger posterior division is primarily sensory, with lingual, inferior alveolar, and auriculotemporal branches; its motor branch is the nerve to the mylohyoid.

  • The maxillary artery branches from the external carotid artery and travels medial to the neck of the mandible. It gives rise to several branches, including the middle meningeal artery, which is seen here surrounded by two roots of the closely associated auriculotemporal nerve. The middle meningeal artery exits the infratemporal fossa by way of the foramen spinosum.

The maxillary artery is one of two terminal branches of the external carotid artery in the parotid gland. It is divided into three segments: mandibular, pterygoid, and pterygopalatine.

The upper image shows the origin of the maxillary artery from the external carotid artery. Note that much of the mandibular ramus of the mandible has been removed, along with the coronoid process and most of the condylar process of the mandible.

• The maxillary artery initially takes a horizontal course medial to the neck of the condyle, and this part of the vessel is termed the mandibular segment.

  • The maxillary artery gives rise to several branches, including those to the ear (deep auricular, anterior tympanic).

  • The maxillary artery gives rise to the middle meningeal artery, which travels superiorly across or through the roots of the auriculotemporal nerve to reach the foramen spinosum, where it enters the middle cranial fossa to supply bone and dura mater.

  • The accessory meningeal artery may branch from the maxillary artery anterior to the middle meningeal. It enters the middle cranial fossa via the foramen ovale, supplying muscular and neural structures in the infratemporal fossa.

  • The inferior alveolar artery is the only inferior branch of the mandibular segment of the maxillary artery. It has a similar course as the inferior alveolar nerve, entering the mandibular foramen to supply mandibular teeth and emerging onto the face as the mental artery to supply the chin.

• The maxillary artery courses anteriorly to assume a position adjacent to the lateral pterygoid muscle (either medial or lateral to it); thus the term pterygoid segment. These branches are represented on both images.

  • The pterygoid segment of the maxillary artery gives rise to branches to the muscles of mastication, including deep temporal arteries, pterygoid arteries, and masseteric artery. It also produces the buccal artery, which travels with the (long) buccal nerve of CN V ₃ , supplying structures of the cheek.

• The maxillary artery finally reaches the pterygomaxillary fissure, where it enters the pterygopalatine fossa; thus the term pterygopalatine segment. Branches from this segment can be seen on both images.

  • The pterygopalatine segment of the maxillary artery displays branches that travel with branches of CN V ₂ in the pterygopalatine fossa.

  • The posterior superior alveolar artery branches from the maxillary artery and enters small foramina on the posterior surface of the maxilla to supply the maxillary molars.

  • The infraorbital artery courses anteriorly from the maxillary artery, passing through the inferior orbital fissure, infraorbital groove, and infraorbital canal and emerging onto the face through the infraorbital foramen.

  • The descending palatine artery is the only inferior branch from this part of the maxillary artery. It divides into greater and lesser palatine arteries, which supply the hard and the soft palate, respectively.

  • The sphenopalatine artery is the continuation of the pterygopalatine segment of the maxillary artery. It exits the pterygopalatine fossa by way of the sphenopalatine foramen to enter the nasal cavity, where it gives rise to posterior septal and posterolateral nasal branches.

  • The pterygopalatine segment of the maxillary artery also gives rise to the pharyngeal artery, which travels through the pharyngeal canal to supply the region of the nasopharynx.

  • The artery of the pterygoid canal travels with the pterygoid nerve to supply the region of the nasopharynx. This vessel may also arise from the internal carotid artery.

In addition to maxillary artery branches, the lower image demonstrates several deep branches from the facial artery of the external carotid artery.

• Note the ascending pharyngeal and ascending palatine arteries arising from the proximal portion of the facial artery, coursing along the superior pharyngeal constrictor muscle.

• The tonsillar artery is also visible in this view.

This plate highlights the neurovascular anatomy of the infratemporal fossa from an inferolateral view.

• Note that the left side of the mandibular body and ramus has been removed; since the ramus has been resected, the medial pterygoid on the left is cut.

• Because the coronoid process of the mandible has been removed in this image, the temporalis muscle has been reflected superiorly toward the temporal fossa.

• Finally, the condylar process of the mandible is cut, but visible in this plate; note the attachment of the lateral pterygoid muscle to it.

Looking across to the right side of the mandible, observe that a window has been cut in the medial pterygoid muscle on this side to demonstrate superficial nerves in this region.

In addition, the zygomatic arch has been removed in this plate, in order to expose deep structures in the temporal and infratemporal fossae.

Begin your study of this plate with the common carotid artery.

• Note that it divides into a more anterior external carotid and most posterior internal carotid artery.

• The internal carotid artery does not have any branches in the neck, while the external carotid artery has multiple branches.

• One mnemonic to remember the branches of the external carotid artery is “Some Little Fat Man Stole Papa’s Only Apple.” Superior thyroid artery (Some) descends as the first branch from the external carotid artery. Moving superiorly, the next branch is the lingual artery (Little). Next, the facial artery (Fat) arises and cross over the angle of the mandible to reach the face. The two terminal branches of the external carotid artery are the maxillary artery (Man) and the superficial temporal artery (Stole). Continuing posteriorly, there is a posterior auricular artery (Papa’s) which is not shown. The occipital artery (Only) courses posteriorly to the occipital region of the skull. Finally, the ascending pharyngeal artery (Apple) branches from the bifurcation of the external and internal carotid arteries but is not visible in this plate.

The maxillary artery courses across the infratemporal fossa and is divided into three segments: a mandibular, a pterygoid and a pterygopalatine portion.

The mandibular segment of the maxillary artery gives rise to a deep auricular, anterior tympanic, middle meningeal and inferior alveolar artery.

• Note that the middle meningeal artery has a close anatomical relationship with the auriculotemporal branch of the mandibular division of the trigeminal nerve as it travels toward the foramen spinosum to enter the skull.

• The inferior alveolar artery travels superficial to the medial pterygoid muscle en route to enter the mandible and provide innervation to the mandibular teeth.

The pterygoid segment of the maxillary artery supplies the muscles of mastication, including the anterior and posterior deep temporal arteries and the buccal artery.

Finally, the pterygopalatine segment of the maxillary artery gives rise to the infraorbital and posterior superior alveolar arteries.

• Note the infraorbital artery approaching the inferior orbital fissure en route to the orbital floor, while the posterior superior alveolar (PSA) arterial branches enter foramina in the posterior maxilla.

Next, we will draw our attention to the branches of the mandibular division of the trigeminal nerve in the infratemporal fossa.

• Begin with the mandibular nerve passing through foramen ovale. Branching posteriorly from the mandibular nerve, note the auriculotemporal nerve and its close relationship with the middle meningeal artery. Also trace the auriculotemporal nerve superiorly, as it travels with the superficial temporal artery.

• Next, follow the inferior alveolar and lingual nerves, as they descend on the superficial surface of the medial pterygoid muscle. Note the chorda tympani nerve, a branch of the facial nerve, as it joins the lingual nerve in the infratemporal fossa. Note the submandibular ganglion suspended from the inferior edge of the lingual nerve in the floor of the mouth. Continuing our study of mandibular nerve branches, identify the buccal nerve, which passes between the superior and inferior heads of the lateral pterygoid muscle. Finally, observe the deep temporal nerves innervating the deep surface of the temporalis muscle.

This plate highlights the anatomy of the terminal branches of the external carotid artery—the maxillary and superficial temporal arteries.

In the upper image (lateral view), first identify the external carotid arteries.

• On the left, the lingual and facial branches are visible on the deep surface of the mandible.

• On the right, note the external carotid artery, continuing superiorly as the superficial temporal artery.

• The maxillary artery courses deep to the mandibular condyle and is visible while peering through the mandibular notch into the infratemporal fossa on the right.

In the lower image (medial view), begin inferiorly at the external carotid artery, and note its lingual and facial branches. Superiorly, note its termination as the maxillary and superficial temporal arteries. The maxillary artery may be divided into three segments: mandibular, pterygoid, and pterygopalatine ( not shown here ).

• In its mandibular segment, the maxillary artery gives rise to deep auricular and anterior tympanic arteries that supply the middle ear.

• Next, the maxillary artery branches to form the middle meningeal artery, which also courses superiorly to reach the foramen spinosum.

• The maxillary artery also gives rise to the inferior alveolar artery, which enters the mandibular foramen to supply the mandibular teeth.

• In its pterygoid portion, the maxillary artery supplies the muscles of mastication via the masseteric artery and deep temporal arteries.

The upper image elucidates the branches of CN V ₃ in the infratemporal fossa from a lateral view, with the ramus and much of the mandibular body removed. CN V ₃ , the mandibular nerve, enters the infratemporal fossa via the foramen ovale and immediately divides into anterior and posterior divisions.

• The anterior division is primarily motor to muscles of mastication, with the (long) buccal nerve being the only sensory branch.

  • The motor branches include deep temporal nerves to the temporalis muscle, the masseteric nerve, and nerves to the medial and lateral pterygoid muscles.

  • The buccal branch of CN V ₃ is sensory to the buccal mucosa and to the skin overlying the buccinator. It emerges between the superior and inferior heads of the lateral pterygoid muscle.

• The posterior division is primarily sensory, with the nerve to the mylohyoid being the only motor branch.

  • The lingual nerve provides general sensation from the anterior two thirds of the tongue. This nerve has several “hitchhikers,” where taste and parasympathetic fibers travel with it for a short distance before reaching their targets.

  • The chorda tympani is a branch of CN VII and is seen uniting with the lingual nerve posteriorly. The chorda tympani carries taste sensation from the anterior two thirds of the tongue, along with presynaptic parasympathetic fibers destined to synapse in the submandibular ganglion.

  • The submandibular ganglion is a parasympathetic ganglion that hangs inferiorly from the lingual nerve in the floor of the oral cavity. This ganglion gives rise to postsynaptic parasympathetic fibers that will innervate the sublingual and submandibular salivary glands.

  • The inferior alveolar nerve provides general sensation to the mandibular teeth and gingivae. It emerges from the mandible through the mental foramen to innervate the skin of the chin.

  • The nerve to the mylohyoid muscle branches from the inferior alveolar nerve just proximal to the entry of the inferior alveolar nerve into the mandible foramen. The nerve to the mylohyoid travels medial to the mandible in the mylohyoid groove to reach and innervate the mylohyoid and the anterior belly of the digastric muscle.

  • The auriculotemporal nerve branches posteriorly from the posterior division of CN V ₃ and has a close anatomical association with the middle meningeal artery; shown here splitting around it. The auriculotemporal nerve provides general sensation to the temporomandibular joint, along with the skin of the temporal fossa, tragus, and neighboring helix of the external ear.

The lower image elucidates the anatomy of CN V ₃ in the infratemporal fossa from a medial view. To orient yourself in this image, note that the anterior aspect of the head is to the left and the posterior aspect is to the right. The posterior portions of the nasal concha are visible on the left side of the image, along with the sphenoid sinus above and molar teeth below.

Part of the middle cranial fossa is visible in the lower image, with the motor and sensory roots of CN V ₃ . The sensory root has its cell bodies in the trigeminal, or semilunar ganglion, from which CNs V ₁ , V ₂ , and V ₃ emerge. CN V ₃ exits the middle cranial fossa by way of the foramen ovale to enter the infratemporal fossa.

• The anterior division of CN V ₃ is seen branching from CN V ₃ . It gives rise to motor branches to the muscles of mastication (a branch to the medial pterygoid is seen here), along with other pharyngeal arch 1–derived muscles, such as the tensor veli palatini and tensor tympani.

  • The tensor veli palatini is visible on this image, with its tendon related to the hamulus of the medial pterygoid plate inferiorly.

  • The tensor tympani is visible attaching along the bony part of the pharyngotympanic tube on the anterior aspect of the middle ear cavity.

• The posterior division of CN V ₃ has a swelling, the otic ganglion, on its medial surface.

  • The otic ganglion is the parasympathetic ganglion associated with CN IX that innervates the parotid gland.

  • The lesser petrosal nerve of CN IX can be seen coursing through the middle cranial fossa and entering foramen ovale to synapse in the otic ganglion.

  • Postsynaptic parasympathetic fibers then exit the ganglion and “hitch a ride” on the auriculotemporal nerve of CN V ₃ to reach the parotid gland.

  • The auriculotemporal nerve branches from the posterior root of CN V ₃ and has a close relationship with the middle meningeal artery from the maxillary artery.

  • The lingual nerve branches from the posterior roof of CN V ₃ inferiorly and unites with the chorda tympani of CN VII. The chorda tympani branches from CN VII in the facial canal, then courses along the lateral wall of the middle ear cavity before entering the infratemporal fossa via the petrotympanic fissure.

  • The inferior alveolar nerve branches from the posterior root of CN V ₃ and enters the mandibular foramen to supply the mandibular teeth with pulpal innervation. Just proximal to the mandibular inferior alveolar foramen, note the branching of the nerve to the mylohyoid, which will travel medial to the mandible and lateral to medial pterygoid muscle to reach its target muscles, the mylohyoid and anterior belly of the digastric.

For orientation in this superior view of the infratemporal fossa and cranial fossae, note the temporalis muscle ( cut ) attaching to the coronoid process of the mandible on the right.

Within the cranial fossae, identify the optic nerves emerging from the optic canals and merging at the optic chiasm. Just lateral to the right optic nerve, note the internal carotid artery. Posterior to the internal carotid artery, identify cranial nerves (CNs) III, IV, and V.

CN V enlarges over the petrous ridge to form the trigeminal ganglion, from which CNs V ₁ , V ₂ , and V ₃ emerge. CN V ₃ exits the middle cranial fossa via the foramen ovale to enter the infratemporal fossa.

CN V ₃ has been cut and reflected anterolaterally in this view. Note the parasympathetic otic ganglion on its deep surface.

CN V ₃ can be divided into an anterior and a posterior division.

• The anterior division gives rise to the buccal nerve and motor branches to the muscles of mastication, including the deep temporal nerves to the temporalis muscle and the masseteric nerve.

• The posterior division of CN V ₃ includes the inferior alveolar nerve and lingual nerve, along with the auriculotemporal nerve, which is visible passing posterior to the temporomandibular joint (TMJ).

The TMJ is formed by the condylar head of the mandible and the mandibular fossa of the temporal bone ( removed here ). Note the articular disc overlying the mandibular condyle. The fibrous joint capsule of TMJ has been cut.

Posterior to TMJ, note the external carotid artery, as it divides into the superficial temporal and maxillary arteries. This branching occurs within the parotid salivary gland.

The maxillary artery gives rise to multiple branches within the infratemporal fossa, including the deep temporal and masseteric arteries.

Demonstrates well the course of CN V ₁ and CN V ₂ from a lateral view. This is a parasagittal section through the head, allowing visualization of the middle cranial fossa on the left side of the image, the orbit and pterygopalatine fossa, and finally the face to the right.

Starting in the cranial cavity, note the trigeminal nerve, which expands distally to form the trigeminal sensory ganglion, from which V ₁ , V ₂ , and V ₃ emerge.

CN V ₁ , the ophthalmic nerve, exits the cranial cavity by way of the superior orbital fissure, giving rise to three main branches: frontal, nasociliary, and lacrimal nerves.

• The frontal nerve is largest and branches to form a more lateral supraorbital and a more medial supratrochlear nerve. These branches exit the orbit to reach the forehead, where they supply general sensation.

• The nasociliary nerve branches medially and deep from CN V ₁ and gives rise to anterior and posterior ethmoidal nerves that supply the mucosa of the ethmoid air cells.

  • The nasociliary nerve gives rise to fibers that travel through the ciliary ganglion (parasympathetic ganglion of CN III) and emerge as long and short ciliary nerves to the eyeball.

  • The terminal branches of the nasociliary nerve are the anterior ethmoidal nerve, which becomes the external nasal nerve, and the infratrochlear nerve, which supplies the root of the nose and structures medial to the orbit.

    • The lacrimal nerve branches laterally from CN V ₁ to reach the lacrimal gland and the superolateral skin of the eyelid. The lacrimal nerve receives postsynaptic parasympathetic fibers from the pterygopalatine ganglion that will provide secretomotor innervation to the lacrimal gland; these parasympathetics “hitch a ride” on the lacrimal nerve to reach their target.

      • Postsynaptic parasympathetic fibers from the pterygopalatine ganglion (associated with CN VII) travel superiorly via ganglionic branches to hitch a ride on CN V ₂ .

      • From CN V ₂ , parasympathetics travel on the zygomatic nerve of V ₂ , and finally the zygomaticotemporal nerve. A communicating branch from the zygomaticotemporal nerve to the lacrimal nerve runs along the lateral wall of the orbit to carry these autonomic fibers to the lacrimal nerve and ultimately the lacrimal gland.

CN V ₂ , the maxillary nerve, exits the cranial cavity by way of the foramen rotundum, leading it to the pterygopalatine fossa.

• The pterygopalatine fossa is seen through the pterygomaxillary fissure, the lateral entrance into the fossa.

• In the pterygopalatine fossa, CN V ₂ gives rise to several branches, including the zygomatic nerve, posterior superior alveolar nerves, and infraorbital nerve, along with other branches that travel inferiorly through the pterygopalatine ganglion without synapsing (greater and lesser palatine nerves, pharyngeal nerve, nasal nerves).

  • The zygomatic nerve of CN V ₂ splits into two branches, including the zygomaticofacial and zygomaticotemporal nerves, which provide general sensation to the skin over the cheek and anterior temporal region.

  • The posterior superior alveolar (PSA) nerves give rise to branches that enter the maxilla to supply the maxillary molars with pulpal innervation. In addition, the PSA nerves branch to supply the vestibular gingiva associated with the maxillary molar teeth; these branches do not enter the maxilla and are not shown on this image.

  • The infraorbital nerve is the anterior continuation of CN V ₂ and exits the pterygopalatine fossa by way of the inferior orbital fissure, then travels through the infraorbital groove and canal in the maxilla. Here, the infraorbital nerve gives rise to two branches to the anterior maxillary teeth, the middle and anterior superior alveolar nerves.

  • The middle superior alveolar nerve supplies the premolars and mesiobuccal root of the first molar with pulpal innervation; it also supplies the vestibular gingiva of the premolars.

  • The anterior superior alveolar nerve supplies the incisor and canine teeth with pulpal innervation; it also supplies the vestibular gingiva of these teeth.

  • The infraorbital nerve exits the infraorbital canal onto the face by way of the infraorbital foramen.

The pterygopalatine ganglion hangs inferiorly from CN V ₂ in the pterygopalatine fossa, suspended by ganglionic branches.

• This parasympathetic ganglion contains the postsynaptic cell bodies that supply the lacrimal, nasal, and palatal glands. It can be thought of as the “hay fever” ganglion because its activation makes the eyes water and the nose drip.

• The nerve of the pterygoid canal delivers presynaptic parasympathetic fibers that synapse in the pterygopalatine ganglion. The nerve of the pterygoid canal also carries postsynaptic sympathetic fibers.

• The nerve of the pterygoid canal can be seen entering the ganglion posteriorly.

Several sensory branches of CN V ₂ pass through the ganglionic branches into the pterygopalatine ganglion without synapsing. They pick up autonomic fibers in this way. The greater and lesser palatine nerves are seen coursing out of the pterygopalatine ganglion inferiorly.

The nasal cavity is lined by respiratory mucosa that contains glands requiring autonomic innervation, including parasympathetic and sympathetic fibers. Plate elucidates the course of origin and course of these fibers.

The parasympathetic innervation to the nasal cavity arises from cranial nerve (CN) VII in the superior salivatory nucleus, where the presynaptic cell bodies are housed (shown in blue on this figure).

• The presynaptic fibers exit the salivary nucleus and travel through the facial nerve.

• The facial nerve enters the temporal bone via the internal acoustic meatus.

• In the temporal bone, the facial nerve branches at the level of the geniculum; much of the facial nerve courses inferiorly through the facial canal.

• Some presynaptic parasympathetic fibers, however, branch anteriorly at the level of the geniculate ganglion to form the greater petrosal nerve. The greater petrosal nerve exits the temporal bone and enters the middle cranial fossa through the hiatus of the greater petrosal nerve. It courses over the foramen lacerum to approach the posterior opening of the pterygoid canal. Here, it will join with the sympathetic deep petrosal nerve to form the nerve of the pterygoid canal.

Sympathetics to the nasal cavity arise in the upper segments of the intermediolateral nucleus of the spinal cord.

• These presynaptic sympathetic fibers ascend to synapse in the superior cervical sympathetic ganglion.

• Postsynaptic sympathetic fibers from the superior cervical ganglion travel along the internal carotid artery as the carotid plexus.

• Some of these fibers branch to form an independent nerve, the deep petrosal nerve, which joins the greater petrosal nerve at the pterygoid canal.

The nerve of the pterygoid canal thus contains both presynaptic parasympathetic and postsynaptic sympathetic fibers.

The nerve of the pterygoid canal enters the pterygopalatine fossa posteriorly and enters the pterygopalatine ganglion, where the parasympathetic fibers synapse. Postsynaptic parasympathetic and postsynaptic sympathetic fibers then exit the ganglion and “hitch a ride” on branches of CN V ₂ to reach their targets in the nasal cavity.

Demonstrates the pterygopalatine fossa from an anterior perspective, with much of the lower facial skeleton resected to reveal the neurovascular contents of this region. On the left side of the donor, branches of maxillary artery are shown, while on the right side, you can see the branches of cranial nerve (CN) V ₂ and the pterygopalatine ganglion.

CN V ₂ , the maxillary nerve, enters the pterygopalatine fossa via the foramen rotundum and gives rise to several branches in this region.

• The zygomatic nerve arises from the maxillary nerve, traveling through the inferior orbital fissure and branching into zygomaticofacial and zygomaticotemporal branches that supply general sensation to the skin over the cheek and temple.

  • Note the presence of a communicating branch between the zygomaticotemporal nerve of CN V ₂ and the lacrimal nerve of CN V ₁ ; this branch transmits parasympathetic fibers to the lacrimal gland.

• The infraorbital nerve is the anterior continuation of the maxillary nerve. It exits the pterygopalatine fossa via the inferior orbital fissure, then travels through the infraorbital groove and canal in the roof of the maxillary sinus. The infraorbital nerve gives rise to several branches in the infraorbital canal, including the anterior and middle superior alveolar nerves, which course along the walls of the maxillary sinus to supply the anterior maxillary teeth. Inflammation of the maxillary sinus can affect these nerves and refer pain to the maxillary teeth.

• The posterior superior alveolar nerve branches from the maxillary nerve in the pterygopalatine fossa and then exits by way of the pterygomaxillary fissure to reach the infratemporal fossa. Here, it enters foramina in the maxilla to pass through the maxillary sinus to reach the maxillary molars and supply them with pulpal innervation.

• The maxillary nerve gives rise to ganglionic branches, which convey sensory fibers through the pterygopalatine ganglion without synapsing.

  • Sensory branches of the maxillary nerve that emerge from the pterygopalatine ganglion seen here, including nasal nerves along with greater and lesser palatine nerves.

• The pterygopalatine ganglion receives autonomic fibers from the nerve of the pterygoid canal posteriorly, just medial and inferior to the foramen rotundum.

The maxillary artery, visible on the left side of this donor, is a terminal branch of the external carotid artery, along with the superficial temporal artery. The maxillary artery is organized into three segments: mandibular, pterygoid, and pterygopalatine.

The pterygopalatine portion of the maxillary artery gives rise to several branches, responsible for supplying the nasal cavity, nasopharynx, palate, maxillary teeth, and face.

• • The posterior superior alveolar artery supplies the molar teeth.

  • The infraorbital artery gives rise to the middle and anterior superior alveolar arteries, which travel through the maxillary sinus to reach and supply the premolar and anterior maxillary teeth. The infraorbital artery ultimately emerges onto the face by way of the infraorbital foramen.

  • The sphenopalatine artery supplies the nasal cavity.

  • The artery of the pterygoid canal and pharyngeal artery supply the region of the nasopharynx.

Represents a parasagittal section through the head, lateral to the entry of the facial nerve, into the temporal bone via the internal acoustic meatus. The mandible has been removed, along with muscles and other soft tissue, to expose the neurovasculature of the skull base.

The common carotid artery is visible at the inferior aspect of this image, dividing into the internal and external carotid arteries between C3 and C5 vertebral levels.

• The cervical segment of the internal carotid artery ascends through the neck without branching to reach the carotid canal in order to enter the skull base. At the level of the superior cervical ganglion, postsynaptic sympathetic fibers invest the internal carotid artery as the carotid plexus.

• The petrous segment of the internal carotid artery courses through the temporal bone, passes over the foramen lacerum, and enters the cavernous sinus within the middle cranial fossa. It gives rise to the ophthalmic artery and then transitions to its communicating segment, which terminates as anterior and middle cerebral arteries.

The facial nerve enters the temporal bone via the internal acoustic meatus.

• The facial nerve then takes a turn inferiorly at the level of the geniculate ganglion to travel in the facial canal.

• The main trunk of the facial nerve emerges from the facial canal at the skull base by way of the stylomastoid foramen.

• While still in the temporal bone, the facial nerve gives rise to a presynaptic parasympathetic branch, the greater petrosal nerve, at the level of the geniculate ganglion.

• The greater petrosal nerve joins the postsynaptic sympathetic deep petrosal nerve to form the nerve of the pterygoid canal.

• This nerve of the pterygoid canal enters the pterygopalatine fossa and delivers autonomic fibers to the pterygopalatine ganglion.

• Autonomic fibers from this ganglion travel along branches of the maxillary nerve (CN V ₂ ) to supply its glandular targets (including the greater and lesser palatine nerves shown on this diagram).

A number of cranial nerves exit the skull base via the jugular foramen, including CNs IX, X, and XI. Their relationships to the internal carotid artery and internal jugular vein are shown.

When inspecting the oral cavity, several key anatomical landmarks are reliably visible.

On the upper image, the dorsum of the tongue is depressed to visualize the palate and palatine arches.

• The soft palate should appear symmetrical, with the uvula extending inferiorly in midline.

• Laterally, the palatine tonsils should be visible, flanked by the palatine arches. The palatoglossal arch lies anteriorly, while the palatopharyngeal arch lies posterior to the palatine tonsil on each side.

On the middle right image, the tongue is elevated to expose its ventral surface.

• The frenulum of the tongue is a midline mucosal fold that anchors the tongue to the floor of the mouth.

• Just lateral to where the frenulum attaches to the floor of the oral cavity, note the sublingual caruncles, where the submandibular duct (of Wharton) opens to drain saliva.

• Just lateral to the sublingual caruncle, a sublingual fold is apparent, formed by the sublingual salivary gland. Multiple openings of the sublingual gland’s ducts are visible along this fold.

• Following the frenulum anteriorly (superiorly in this image with the tongue elevated), the fimbriated fold may be observed. Deep to the lingual mucosa in this region, the deep lingual artery and vein along with the lingual nerve are found.

The lower left image demonstrates well the parotid papilla, where the parotid duct drains saliva opposite the second maxillary molar tooth.

The upper image elucidates sensory innervation zones in the palate, pharynx, and tongue from an anterior view.

• The trigeminal nerve provides general sensation to the hard and soft palate, as well as the vestibular gingiva.

• The intermediate nerve (of Wrisberg) from the facial nerve provides some taste innervation from the soft palate. The glossopharyngeal nerve provides general sensation to the walls of the oropharynx, as well as general sensation and taste from the posterior tongue.

• The vagus nerve provides general and taste sensation to the root of the tongue and taste buds on the epiglottis.

The middle image shows the sensory innervation patterns from a midsagittal view.

• The hard and soft palates are primarily innervated by branches of cranial nerve (CN) V ₂ , with CN VII contributing some taste innervation from the soft palate.

• The anterior tongue receives its general sensation from the lingual nerve of CN V ₃ , while CN VII provides taste innervation via the chorda tympani.

• The buccal mucosa is supplied by the buccal branch of CN V ₃ .

• The teeth receive their innervation from the inferior alveolar nerve of CN V ₃ .

• Moving posteriorly into the pharynx, the nasopharynx is largely supplied with general sensation via the pharyngeal branch of CN V ₂ .

• The oropharynx is supplied by CN IX, while the laryngopharynx, or hypopharynx, is innervated by CN X.

The lower image shows the full extent of sensory innervation on the dorsum of the tongue.

• The anterior two thirds of the tongue receives its general sensation from the lingual nerve of CN V ₃ and taste from the chorda tympani nerve of CN VII.

• The posterior one third is largely supplied with general sensation and taste by CN IX, while the region over the epiglottis is supplied by CN X.

The upper image demonstrates the palate from an anterior perspective, whereas the lower image shows the soft palate from a posterior view.

In the upper image, first identify the palatine tonsil on either side, flanked anteriorly by the palatoglossal arch (mucosal fold covering palatoglossus muscle) and posteriorly by the palatopharyngeal arch (mucosal fold covering palatopharyngeus muscle).

Moving lateral from the palatine arches, you can see the pterygomandibular raphe, which extends from the hamulus of the medial pterygoid plate to the deep surface of the mandible, posterior to the last molar. The pterygomandibular raphe serves as an attachment for both the superior pharyngeal constrictor muscle and the buccinator muscle.

The soft palate consists of the interdigitation of several different skeletal muscles, minor salivary glands, and overlying mucosa.

• The uvula contains its own uvular muscle.

• Anterior to the uvula, the levator veli palatini muscle fibers interdigitate left to right to reinforce and elevate the soft palate.

• Anterior to the levator veli palatini muscles, there is a fibrous palatine aponeurosis, formed by the tendons of the tensor veli palatini muscles, which hook around the hamulus of the medial pterygoid plate.

• The palate is innervated by the greater palatine nerve (hard palate) and lesser palatine nerve (soft palate). These are branches of CN V ₂ that carry general sensory fibers, along with autonomic fibers to innervate the palatal glands. Blood vessels with the same names supply the palate and are branches of the descending palatine artery from the maxillary artery.

• The mucosa overlying the hard palate is specialized anteriorly at the incisive papilla and the transverse palatine folds.

The lower image represents a view of the nasal cavity and palate from a posterior view, as if standing in the pharynx looking anteriorly. The basilar part of the occipital and temporal bones has been sectioned coronally; the carotid canal is visible in the temporal bone.

• The vomer of the nasal septum is visible, creating the choanae, or internal nares that represent the doorway between the nasopharynx and nasal cavity. The middle and inferior nasal conchae are visible through the choanae.

• The muscular wall of the nasopharynx is formed by the pharyngobasilar fascia and the superior pharyngeal constrictor muscle.

• The cartilaginous part of the pharyngotympanic tubes is visible, extending into the nasopharynx. Two muscles are closely associated with the pharyngotympanic tube, including levator veli palatini (innervated by CN X) and tensor veli palatini (innervated by CN V ₃ ). These muscles can assist in equalizing pressure between the middle ear and nasopharynx.

• The course of the tendon of the tensor veli palatini is well demonstrated, passing inferior to the hamulus of the medial pterygoid plate and inserting into the palatine aponeurosis.

The upper image is a horizontal, transverse, or cross section through the oral cavity and surrounding anatomical regions.

• First, it is important to orient yourself to key landmarks. The lower lip is visible anteriorly, while the body of the C2 vertebra is located posteriorly. Note the position of the ramus of the mandible laterally, with the inferior alveolar neurovascular bundle at the mandibular foramen. The nerve to the mylohyoid muscle is shown medial to the inferior alveolar neurovascular bundle, just distal to its origin from the inferior alveolar nerve.

• The core of each cheek is formed by the buccinator muscle of facial expression, which attaches posteriorly to the pterygomandibular raphe located just posterior and lateral to the third molar tooth. The superior pharyngeal constrictor muscle attaches to this raphe from behind, forming the muscular core of the wall of the oropharynx at this level.

• Intraorally, note the palatine arches (pillars of the fauces), including the palatoglossal arch (fold) anteriorly and the palatopharyngeal arch (fold) posteriorly. Each arch is formed by mucosa covering a slender skeletal muscle (palatoglossus in palatoglossal arch and palatopharyngeus in palatopharyngeal arch). Palatoglossus and palatopharyngeus muscles receive their motor innervation from the vagus nerve, as do most muscles of the pharynx and palate (except the stylopharyngeus muscle, which is supplied by the glossopharyngeal nerve). Note the palatine tonsil, located between the palatoglossal and palatopharyngeal arches.

• Moving laterally and superficially, into the face and infratemporal fossa, note the position and shape of the ramus of the mandible. The masseter muscle lies superficial to the ramus, while the medial pterygoid muscle lies medial to it.

• Just deep to the medial pterygoid, note a set of muscles arising from the styloid process of the temporal bone, including the styloglossus, stylopharyngeus, and stylohyoid. The styloglossus is innervated by cranial nerve (CN) XII, stylopharyngeus by CN IX, and stylohyoid by CN VII.

• Posterior to the muscles attaching to the styloid process, note the carotid sheath, with the internal jugular vein, internal carotid artery, and vagus nerve within its boundaries. The glossopharyngeal nerve also travels within the sheath for a short distance, located anterior to the vessels, while the hypoglossal nerve travels posteriorly.

• The parotid bed is clearly demonstrated in this view, filled by the parotid gland. Superficially, the parotid gland extends anteriorly from the sternocleidomastoid muscle toward the superficial surface of the masseter muscle. The intermediate portion of the parotid gland is sandwiched between the sternocleidomastoid and mandibular ramus. The deepest portion of the parotid gland courses medially toward the styloid process and muscles attaching to it (styloglossus, stylopharyngeus, stylohyoid), lying posterior to the medial pterygoid muscle and anterior to the posterior belly of the digastric muscle.

• Traveling through the parotid gland are the external carotid artery, retromandibular vein, and facial nerve.

The lower image is a coronal section through the oral cavity, cheek, face, and submandibular triangle.

• Two of the three pairs of salivary glands are visible in this section, the submandibular and sublingual.

• First, it is important to become oriented to key landmarks on this coronal section, taken posterior to the first molar. The buccinator muscle is the muscular core of the cheek. The body of the mandible is visible, with the inferior alveolar neurovascular bundle present in the mandibular canal. The hyoid bone is positioned inferiorly, showing several of its muscular attachments. The tongue is located centrally in this fragment.

• Beginning with the tongue, note the complex arrangement of skeletal muscle fibers forming the intrinsic muscles of the tongue, including longitudinal and transverse. Several extrinsic muscles of the tongue are shown here, attaching the tongue to a neighboring bony landmark.

  • The styloglossus is prominent on the superolateral aspect of the tongue, attaching to the styloid process of the temporal bone.

  • The hyoglossus extends inferiorly to attach to the hyoid bone. It is an important landmark in terms of neurovasculature, with the lingual artery traveling deep to it, while the submandibular duct, lingual nerve, and hypoglossal nerve travel superficial to it. The submandibular gland also lies lateral and superficial to the hyoglossus.

  • The genioglossus forms the central muscular core of the tongue inferiorly as it courses to attach to the genu, or bend, of the mandible anteriorly.

  • Remember that all intrinsic and extrinsic muscles of the tongue are innervated by CN XII, except the palatoglossus, which is considered a palatal muscle and thus is supplied by CN X.

• The mylohyoid muscle forms the floor of the mouth, spanning from the mylohyoid line of the mandible superiorly to the hyoid bone inferiorly.

• Inferior to the mylohyoid, note the submandibular gland and its close relationship to the body of the mandible. It creates a depression in the mandible, the submandibular fossa.

• The facial artery and vein have a distinct relationship with the submandibular vein in this region. The facial artery travels deep to the submandibular gland, whereas the facial vein courses superficial to the gland.

The images highlight the anatomical relationships of the suprahyoid muscles. Suprahyoid muscles attach to the upper pole of the hyoid bone, thereby elevating it when they contract. Elevation of the hyoid bone occurs during swallowing and speaking.

The digastric muscle is a two-bellied muscle with an intermediate tendon tethered to the hyoid bone by a connective tissue pulley, or fibrous loop.

• The anterior belly attaches to the digastric fossa on the deep surface of the mandibular body of the mandible and is innervated by the nerve to the mylohyoid muscle from CN V ₃ .

• The posterior belly attaches along the mandibular notch of the temporal bone and is innervated by CN VII.

• The difference in innervation between the bellies results from the embryonic origin of each muscle belly (anterior belly from pharyngeal arch 1, innervated by CN V; posterior belly from pharyngeal arch 2, innervated by CN VII).

The stylohyoid muscle spans from the styloid process of the temporal bone to the hyoid bone.

• The stylohyoid splits around the digastric intermediate tendon before its attachment to the hyoid bone.

• Throughout most of its length, the stylohyoid is located superior to the posterior belly of the digastric muscle.

• The stylohyoid is derived from the second pharyngeal arch and thus is innervated by CN VII.

The mylohyoid muscle lies just deep (superior) to the anterior belly of the digastric muscle on each side.

• The mylohyoid muscles arise from the mylohyoid line on the deep surface of the mandibular body and unite in midline at the median raphe, or connective tissue cord.

• The mylohyoid attaches to the hyoid bone along its posterior surface.

• The mylohyoid is innervated by CN V ₃ , specifically the nerve to mylohyoid.

The hyoglossus muscle helps to complete the floor of the oral cavity by laterally closing off the gap left by the mylohyoid muscle. The hyoglossus is an extrinsic tongue muscle, attaching from the lateral surface of the tongue to the hyoid bone, and is innervated by CN XII.

The geniohyoid muscle lies just deep (superior) to the mylohyoid and attaches from the inferior mental (genial) spine (tubercle) to the body of the hyoid bone. It is innervated by C1 spinal nerve fibers that “hitch a ride” along CN XII.

To summarize the specific muscles forming the floor of the oral cavity, recall the following relationships:

• Superficially, the anterior belly of the digastric muscle runs in an anterior-to-posterior direction.

• Just deep to the anterior digastric muscle, the mylohyoid muscles form a muscular sling under the mandible. Mylohyoid fibers run medial to lateral rather than anterior to posterior.

• Immediately deep to the mylohyoid, the geniohyoid muscle runs anterior to posterior, in parallel with the anterior digastric fibers.

• Laterally, the hyoglossus helps to complete the floor of the oral cavity, spanning from tongue to hyoid bone.

The lower image adds additional structures to the muscular floor of the oral cavity.

• The posterior root of CN V ₃ gives rise to the lingual and inferior alveolar nerves.

  • The lingual nerve travels immediately posterior to the third molar and then courses medially to reach the anterior two thirds of the tongue, deep to the mucosal floor of the oral cavity.

  • The lingual nerve crosses medial to the sublingual gland and inferior to the duct of the submandibular gland as it approaches the tongue.

  • The inferior alveolar nerve and artery enter the mandibular foramen to supply the mandibular teeth, giving rise to the nerve and artery to the mylohyoid just proximal to their entry into the mandible.

• The submandibular gland wraps posteriorly around the mylohyoid muscle, such that the deep portion of the gland lies immediately superior to the mylohyoid in the floor of the oral cavity. The deep portion of the submandibular gland gives rise to the submandibular duct (of Wharton).

• The sublingual gland lies anterior to the deep portion of the submandibular gland and also rests immediately superior to the mylohyoid.

The upper image demonstrates the suprahyoid muscles and their relationship to the extrinsic muscles of the tongue. In this parasagittal section through the head, note the hard palate superiorly and genu of the mandible anteriorly. The anterior and posterior bellies of the digastric muscle have been resected, leaving only the intermediate tendon.

• Starting with the suprahyoid muscles, identify the mylohyoid muscle inferiorly, forming the floor of the oral cavity. Because its fibers run medial to lateral, the mylohyoid is cut in cross section in this view.

• Just superior to the mylohyoid is the geniohyoid muscle, whose fibers run anterior to posterior. It attaches from the inferior mental spine (genial tubercle) to the body of the hyoid bone.

• Just superior to the geniohyoid is the fan-shaped extrinsic tongue muscle known as the genioglossus, because it attaches from the superior mental spine (genial tubercle).

• Lateral and posterior to the genioglossus is the hyoglossus, whose fibers are vertically oriented as they descend from the lateral tongue to the hyoid bone.

• Lateral to the hyoglossus, note the stylohyoid muscle, splitting around the intermediate tendon of the digastric muscle. Superior to the stylohyoid, the styloglossus muscle blends with the fibers of the hyoglossus before inserting into the lateral side of the tongue.

• Medial to the styloglossus is the palatoglossus muscle, spanning from the posterior tongue to the soft palate. Although the palatoglossus attaches to the tongue, it is considered a palatal muscle and is innervated by CN X (not CN XII, as are other extrinsic tongue muscles).

• Posteriorly, identify the superior and middle pharyngeal constrictor muscles, forming the walls of the pharynx. The superior constrictor does not reach the skull base in this view, and the pharyngobasilar fascia closes off the pharynx superiorly. The stylopharyngeus muscle inserts into the pharyngeal wall between the superior and middle pharyngeal constrictor muscles.

The lower image adds neurovascular and ductal elements to the muscles previously outlined. For orientation purposes, note the geniohyoid muscle inferiorly and the genioglossus muscle immediately superior to it. Lateral to the genioglossus, the hyoglossus muscle has been partially resected to reveal neurovascular structures traveling deep to it. The styloglossus blends with the hyoglossus as it approaches the tongue posteriorly. The palatoglossus lies anterior and medial to the styloglossus.

• Two nerves are highlighted in this image, the lingual and hypoglossal.

• The lingual nerve crosses lateral to the hyoglossus muscle en route to the tongue. Note the parasympathetic submandibular ganglion hanging inferiorly from the lingual nerve; this ganglion is the site of synapse for presynaptic fibers in the chorda tympani. Following the lingual nerve anteriorly, note that it passes inferiorly to the submandibular duct before reaching the tongue.

• The hypoglossal nerve courses inferior to the lingual nerve throughout its course, traveling lateral to the hyoglossus muscle.

• The external carotid artery gives rise to the lingual artery, which passes deep to the hyoglossus muscle. The lingual artery first branches to form the dorsal lingual artery, which supplies the root of the tongue. At the anterior border of the hyoglossus, the lingual artery terminates as a deep lingual artery that travels superiorly to the dorsum of the tongue and the sublingual artery, which supplies the floor of the mouth.

• The deep lingual, sublingual, and dorsal lingual veins travel with their respective arteries to drain to the lingual vein, which drains to the common facial vein, which drains into the internal jugular vein. The vein of the hypoglossal nerve may receive drainage from the deep lingual, dorsal lingual, or sublingual vein as it courses superficial to the hyoglossus muscle with CN XII. The deep lingual vein is clinically important because it can rapidly absorb drugs such as nitroglycerin. Drugs use passive diffusion to cross the oral mucosa and subsequently enter vascular capillary beds.

The upper figure represents the dorsal view of the tongue, with neighboring anatomical landmarks. The lower figure is a higher magnification of the mucosal surface of the dorsum, indicated by the box on the upper figure.

The tongue is organized into a root, body, and apex. The root represents the attached portion of the tongue that forms the posterior one third of the tongue. The body makes up the anterior two thirds, with the apex being the most anterior region, or the tip of the tongue. The body of the tongue is divided into right and left halves by the median sulcus.

The root of the tongue is characterized by the presence of lymphoid nodules known as lingual tonsils. The root is attached to the soft palate by the palatoglossal arch. The palatine tonsil is visible in the tonsillar fossa between the palatoglossal and palatopharyngeal arches. Posteriorly, the root of the tongue is anchored to the epiglottis by way of a median and two lateral glossoepiglottic folds. The epiglottis valleculae lie between the median and lateral glossoepiglottic folds on each side and are the site for laryngoscopic blade.

The terminal sulcus divides the root from the body of the tongue. At the apex of the terminal sulcus, the foramen cecum is present as the remnant of the developmental evagination of the thyroglossal duct. Just anterior to the terminal sulcus, the distinctive vallate papillae are present, with their characteristic furrows and numerous taste buds. Fungiform papillae are visible over the anterior two thirds of the tongue’s dorsum, with their characteristic mushroom shape; they contain taste buds. The foliate papillae are located laterally and are typically poorly developed in humans. Finally, the filiform papillae are distributed over the body of the tongue as keratinized projections, giving the tongue its rough texture.

• The fauces (oropharyngeal isthmus) represent the transitional region between the oral cavity and the oropharynx. The palatine arches (palatoglossal and palatopharyngeal) are often called the “pillars” of the fauces because they enclose this area laterally.

• The upper image is a sagittal section through the head. For orientation, note the hard and soft palates, separating the nasal cavity above from the oral cavity below.

• The nasopharynx extends from the skull base to the uvula.

  • Note the opening of the pharyngotympanic tube, with the torus tubarius capping the opening superiorly.

  • Extending posteriorly and inferiorly from torus tubarius, note the salpingopharyngeal fold containing the salpingopharyngeus muscle.

  • The pharyngeal recess is a depression within the nasopharynx, posterior to the salpingopharyngeal fold.

• The oropharynx extends from the soft palate to the epiglottis. It is bounded anteriorly by the root of the tongue and laterally by the palatine arches.

  • The palatoglossal arch is the more anterior arch and contains the palatoglossus muscle, innervated by CN X.

  • The palatopharyngeal arch is the more posterior arch and contains the palatopharyngeus muscle, also innervated by CN X. Between the palatine arches, the palatine tonsil is visible.

In the lower image, the mucosa has been removed to reveal the muscular and neurovascular elements associated with the upper pharynx.

• First, again identify the hard and soft palates for orientation.

• Superior to the soft palate is the nasopharynx, with its characteristic pharyngotympanic tube.

  • Several muscles have attachments to the pharyngotympanic tube, including the tensor and levator veli palatini and the salpingopharyngeus.

  • The tensor veli palatini is the most anterior of these three muscles; its tendon is seen coursing inferiorly to help to form the palatine aponeurosis.

  • The levator veli palatini muscle is positioned directly inferior to the pharyngotympanic tube and is seen inserting directly into the soft palate from above.

  • The salpingopharyngeus muscle extends posteriorly and inferiorly to insert into the pharyngeal wall.

• Inferior to the soft palate is the oropharynx.

  • The muscles forming the core of the palatine arches are visible here, including the palatoglossus and palatopharyngeus muscles.

  • Between these arches is the tonsillar fossa, where the palatine tonsil has been removed in this image.

  • The tonsillar fossa is well vascularized with branches from the ascending pharyngeal, ascending palatine, and dorsal lingual arteries.

  • A lingual branch of CN IX is clearly demonstrated entering the root of the tongue to convey impulses associated with general sensation and taste.

• Finally, note the superior pharyngeal constrictor muscle located superficial to the various longitudinal pharyngeal muscles (e.g., palatopharyngeus, salpingopharyngeus, stylopharyngeus).

This plate highlights the anatomy of the posterior pharynx, with its accompanying neurovascular structures. For orientation, note that the occipital bone has been cut coronally to allow visualization of the pharyngeal constrictor muscles and esophagus.

On the right, all vascular elements are intact, including the carotid arterial system and the internal jugular vein. On the left, the vascular elements have been largely resected to show underlying neural structures.

• The sigmoid dural venous sinuses are visible, transitioning to become the internal jugular vein at the jugular foramen on each side. Cranial nerves (CNs) IX, X, and XI also exit the skull base via the jugular foramen.

• Note the close relationship of the internal carotid artery with the internal jugular vein and vagus nerve.

• The pharyngeal venous plexus is clearly demonstrated on the right side.

On the left, note CNs IX, X, and XI coursing through the jugular foramen into the neck. Medial to these nerves, identify the superior cervical ganglion at the rostral end of the sympathetic trunk.

• Note the stylopharyngeus muscle and CN IX wrapping around its posterior surface to reach the oropharynx and root of the tongue.

• CN X gives rise to a pharyngeal branch that provides motor innervation to the pharyngeal constrictor muscles.

• Inferiorly, CN X branches to form the superior laryngeal nerve, which gives rise to the internal and external laryngeal nerves.

On the right side, follow CN X inferiorly to where it gives rise to the recurrent laryngeal nerve, which loops around the right subclavian artery to ascend and innervate the inferior pharynx and larynx.

Demonstrates the muscles of the pharynx, from a posterior view (on the left side) and with the pharyngeal wall reflected to show the lumen of the pharynx (on the right side).

Note the relationship of the pharynx to the more laterally placed suprahyoid muscles in this view, including the posterior belly of digastric and stylohyoid muscles. The mandible is visible laterally, with its medial pterygoid muscle shown from this posterior view.

Starting on the left side, the vertebral column has been removed to reveal the posterior wall of the pharynx, with the buccopharyngeal fascia removed to show the underlying musculature.

• The skeletal muscles of the pharynx are classified as either circular (pharyngeal constrictors) or longitudinal (stylopharyngeus, salpingopharyngeus, and palatopharyngeus). The pharyngeal muscles are innervated by the vagus nerve, except for the stylopharyngeus, which is supplied by the glossopharyngeal nerve.

• The superior pharyngeal constrictor attaches superiorly to the pharyngeal tubercle of the occipital bone. Note that this muscle does not attach to the skull base laterally, and thus the pharyngeal submucosa and pharyngobasilar fascia can be directly visualized superolaterally to the superior constrictor.

• The middle pharyngeal constrictor attaches to the hyoid bone. Note that one of the longitudinal pharyngeal muscles, the stylopharyngeus, inserts into the pharyngeal wall between the superior and middle pharyngeal constrictors.

• The inferior pharyngeal constrictor attaches to the larynx laterally. Note that the inferior constrictor has a specialized region inferiorly, the cricopharyngeus, which encircles the junction between the pharynx and esophagus.

• The inner circular and outer longitudinal muscular layers of the esophagus can be identified below the cricopharyngeus muscle.

The right side has the pharyngeal wall cut and reflected laterally.

• The circularly arranged pharyngeal constrictor muscles are seen reflected laterally in this image. Note the overlapping arrangement of the constrictor muscles, with the superior constrictor largely covered by the middle constrictor and the middle constrictor covered by the inferior constrictor.

• Starting in the nasopharynx, note the choana leading into the nasal cavity anteriorly.

  • The pharyngotympanic tube is prominent in the nasopharynx, with two muscles attaching to it, the levator veli palatini and salpingopharyngeus.

  • The levator veli palatini inserts into the soft palate below, and the uvula is seen extending inferiorly.

• The oropharynx extends from the soft palate to the epiglottis. The root of the tongue is visible from the oropharynx. Extending laterally from the soft palate, note the palatopharyngeus muscle inserting into the pharyngeal wall.

• The laryngopharynx extends from the epiglottis to the lower border of the cricoid cartilage, here covered by the posterior cricoarytenoid muscle. The internal branch of the superior laryngeal nerve is seen piercing the wall of the piriform recess within the laryngopharynx, to provide sensory innervation to the upper mucosa of the larynx.

Demonstrates the anatomy of the pharynx from a posterior view, as if standing in the retropharyngeal space looking anteriorly. The posterior wall of the pharynx has been cut and reflected to show the internal mucosal anatomy of the pharynx and its communications.

Recall that the nasopharynx extends from the skull base to the uvula of the soft palate.

• Note the presence of the pharyngeal tonsil in the roof of the nasopharynx.

• Just inferior to the pharyngeal tonsil, the vomer is prominent as it separates the left and right choanae, or internal nares. Through the choanae you can see the middle and inferior conchae projecting from the lateral walls of the nasal cavities.

• The torus tubarius of the pharyngotympanic tube is visible on each side, with a mucosal salpingopharyngeal fold extending inferiorly from each. Posterior to this fold is a depression, or pharyngeal recess.

• A fold extending inferior to the torus tubarius contains the levator veli palatini muscle bilaterally. The soft palate is then seen extending posteriorly and inferiorly to terminate in the midline uvula.

The oropharynx extends from the uvula and soft palate to the epiglottis.

• The root of the tongue, with its lingual tonsils, is visible from this view and encloses the oropharynx anteriorly.

• The oropharynx is defined laterally by the palatine arches and the palatine tonsil on each side; only the more posterior palatine arch, the palatopharyngeal, is visible in this plate.

The laryngopharynx extends from the epiglottis to the lower border of the cricoid cartilage of the larynx at the C6 vertebral level.

• The epiglottis guards the entrance to the laryngeal lumen, known as the laryngeal inlet.

• Two mucosal folds (aryepiglottic folds) extend from the epiglottis to the arytenoid cartilages to complete the laryngeal inlet posteriorly.

• Within the aryepiglottic folds, two bumps are visible on each side, created by the cuneiform and corniculate cartilages of the larynx.

• The lamina of the cricoid cartilage (lamina) is located inferior to the aryepiglottic folds.

• Note the depression on either side of the cricoid laminae in the laryngopharynx, known as the piriform recess.

Inferior to the laryngopharynx is the esophagus. Note the trachea, positioned anterior to the esophagus.

Reveals the internal anatomy of the laryngopharynx. This is a posterior view, with the vertebral column removed and the pharyngeal wall cut and reflected bilaterally. The mucosa lining the laryngopharynx has been removed as well.

For orientation, note the position of the epiglottis and the lower border of the cricoid cartilage, because these are the vertical boundaries of the laryngopharynx. The cut edges of the pharyngeal constrictors are lateral in this plate, with the longitudinal palatopharyngeus and stylopharyngeus muscles located deep to them.

The deep surface of the thyroid cartilage is in gray, lateral to the cricoid cartilage in midline.

A neurovascular bundle is seen piercing through the thyrohyoid membrane, with the internal branch of the superior laryngeal nerve and the superior laryngeal artery descending into the upper portion of the piriform recess.

Coming up from below, the right recurrent laryngeal branch of the vagus nerve changes its name as it passes under the inferior constrictor; it becomes the inferior laryngeal nerve at this point and enters the lower portion of the piriform recess.

In addition, several intrinsic muscles of the larynx are visible from this perspective. The arytenoid muscle has oblique and transverse fibers that allow it to adduct the vocal cords. The posterior cricoarytenoid muscle is located on the posterior surface of the cricoid cartilage and is the sole abductor of the vocal cords.

Inferiorly, note the transitional area between the laryngopharynx and esophagus, where Laimer’s triangle is visible. Just superior to this region, the clinically relevant pharyngoesophageal, or Zenker’s, diverticulum can develop.

Demonstrates the pharynx in a midsagittal section through the head and neck.

Note the position of the hard and soft palates, separating the nasal cavity above from the oral cavity below. Identify the mandibular body anteriorly and the hyoid bone inferior to the tongue. The trachea and esophagus are visible in parallel, with the trachea positioned anteriorly and the esophagus posteriorly.

The pharynx is the expanded upper end of the gastrointestinal tract and is continuous with the esophagus at the level of C7. It is a fibromuscular tube whose walls consist of mucosa, fascia, and skeletal muscles. The pharynx is divided into three segments from superior to inferior: nasopharynx, oropharynx, and laryngopharynx, or hypopharynx.

The nasopharynx is the most superior part of the pharynx and extends from the skull base to the uvula of the soft palate. The nasopharynx communicates anteriorly with the nasal cavity through two openings known as choanae, or internal nares. The choanae are separated by the vomer of the nasal septum.

• Several anatomical features characterize the nasopharynx. The cartilaginous part of the pharyngotympanic (auditory, eustachian) tube opens into this region, to allow for pressure to equalize between the middle ear and the atmosphere. In the roof of the nasopharynx, there is a lymphoid mass termed the pharyngeal tonsil ; when enlarged, this is referred to as the adenoid.

The oropharynx is continuous with the nasopharynx inferiorly, extending from the soft palate to the epiglottis. The oropharynx communicates with the oral cavity anteriorly, bounded by the root of the tongue anteriorly and by the palatine arches and palatine tonsil laterally on each side.

The laryngopharynx extends inferiorly from the oropharynx and is located posterior to the larynx (“voice box”). The larynx consists of several cartilages, shown here in sagittal section, including the epiglottis, thyroid cartilage, and cricoid cartilage. The vocal fold housing the vocal cords is visible. The laryngopharynx extends from the tip of the epiglottis to the inferior border of the cricoid cartilage at the C6 vertebral level. The laryngopharynx communicates inferiorly with the esophagus.

Represents a sagittal section through the pharynx, with the mucosa removed to show the underlying skeletal musculature.

For orientation, identify the hard and soft palates, separating the nasal cavity from the oral cavity. The nasal conchae are visible in the nasal cavity, and posterior to them, the medial pterygoid plate can be identified.

• The medial pterygoid plate extends a hook, or hamulus, inferiorly that can be seen just below the soft palate; the tendon of tensor veli palatini muscle extends around this bony hamulus. The pterygomandibular raphe attaches to the hamulus and provides attachment for the buccinator muscle anteriorly and the superior pharyngeal constrictor muscle posteriorly.

• The hyoid bone is visible at the level of C3, providing an attachment site for muscles and ligaments. Note the thyrohyoid membrane connecting the hyoid bone to the thyroid cartilage below.

• Finally, note the position of the larynx just inferior to the hyoid bone, with the thyroid, cricoid, and arytenoid cartilages contributing to its formation. The trachea extends inferior to the larynx. Posterior to the trachea, identify the esophagus.

The nasopharynx extends from the skull base to the uvula of the soft palate.

• The cartilaginous part of the pharyngotympanic tube is a characteristic feature of the nasopharynx, and its medial protrusion is termed the torus tubarius.

• Two muscles are closely associated with the pharyngotympanic tube: the tensor veli palatini and levator veli palatini. The tensor spreads the soft palate laterally to ensure an effective seal between the nasopharynx and oropharynx during swallowing. It is innervated by the trigeminal nerve. The levator veli palatini elevates the soft palate during swallowing and is innervated by the vagus nerve, as are most palatal and pharyngeal muscles.

• Extending posteriorly and inferiorly from the torus tubarius, note the slender salpingopharyngeus muscle, which inserts into the pharyngeal wall; it helps to open the pharyngeal opening of the pharyngotympanic tube and is innervated by the vagus nerve. “Salpingo” refers to the bell of a trumpet, describing the flared appearance of the pharyngotympanic tube.

• The circularly arranged superior pharyngeal constrictor muscle helps to form the wall of the nasopharynx. Superolaterally, however, the superior constrictor muscle does not extend to the skull base, and this deficiency is filled by the submucosal layer of the pharynx, the pharyngobasilar fascia.

The oropharynx extends from the soft palate to the epiglottis (not visible in this image) and communicates with the oral cavity anteriorly.

• The superior and middle pharyngeal constrictor muscles help to form the fibromuscular wall of the oropharynx. The middle constrictor attaches to the hyoid bone.

• Note the stylohyoid ligament extending to the hyoid bone between the superior and middle constrictor muscles.

• The palatine arches are located in the lateral wall of the oropharynx, and the palatopharyngeus muscle within the palatopharyngeal arch is seen here.

The laryngopharynx extends posterior to the larynx; the inferior pharyngeal constrictor muscle forms much of its fibromuscular wall.

The pharyngeal constrictor muscles are invested on their posterior surface by a layer of fascia, the buccopharyngeal fascia, which allows them to glide over the prevertebral fascia covering the anterior surface of the vertebral bodies.

• Between the buccopharyngeal and prevertebral fasciae, the retropharyngeal space is visible. This space is a potential site for infection to track from the head and neck into the mediastinum.

From this lateral view, the anterior attachment sites for the pharyngeal musculature can be clearly observed.

First, identify the circularly arranged pharyngeal constrictor muscles and their respective attachment sites.

The superior constrictor courses laterally to insert into the pterygomandibular raphe. Recall that the buccinator muscles of facial expression originate from this raphe anteriorly. On either side of the superior pharyngeal constrictor muscle, note the more lateral tensor veli palatini and the more medial levator veli palatini muscles.

The middle constrictor attaches to the hyoid bone and the stylohyoid ligament.

The inferior constrictor attaches to the oblique line of the thyroid cartilage and the cricoid cartilage. At its inferior border, the inferior constrictor becomes specialized as the cricopharyngeus muscle, which serves as the upper esophageal sphincter, which is contracted at rest and opens to permit swallowing.

The esophagus blends inferiorly with fibers from the inferior pharyngeal constrictor.

Next, identify the longitudinal pharyngeal muscles that help to elevate the pharynx and larynx during swallowing. The only longitudinal pharyngeal muscle seen in this view is the stylopharyngeus muscle, which courses between the superior and middle pharyngeal constrictor muscles. The stylopharyngeus muscle is innervated by cranial nerve (CN) IX, in contrast to most pharyngeal muscles, which are supplied by CN X.

Additionally shows the suprahyoid muscles that form the floor of the oral cavity. The anterior belly of the digastric muscle lies just inferior to the mylohyoid muscle. The hyoglossus is an extrinsic muscle of the tongue that helps to close off the posterolateral floor of the mouth. Here the hyoglossus is seen blending with another extrinsic tongue muscle, the styloglossus.

This lateral view of the head and neck provides a comprehensive view of the peripheral nerves in the lateral head and neck. Note that the mandibular angle and ramus have been removed, along with sternocleidomastoid, posterior digastric, masseter, and lateral pterygoid muscles.

The trigeminal nerve is represented by its maxillary (CN V ₂ ) and mandibular (CN V ₃ ) nerves.

CN V ₂ , the maxillary nerve, provides sensory innervation to the cheek.

• CN V ₂ passes through the pterygopalatine fossa (seen here through the pterygomaxillary fissure) and has a close anatomical relationship with the parasympathetic pterygopalatine ganglion.

• CN V ₂ gives rise to the greater and lesser palatine nerves that supply the hard and soft palates, as well as posterior superior alveolar nerves that supply the maxillary molars.

• CN V ₂ continues anteriorly as the infraorbital nerve, which branches to form the anterior and middle superior alveolar nerves that supply the pulp of the anterior teeth.

• The infraorbital nerve finally emerges onto the face to provide general sensation to the midface.

CN V ₃ , the mandibular nerve, enters the infratemporal fossa via the foramen ovale. It immediately splits into anterior and posterior divisions.

• The anterior division is primarily motor to the muscles of mastication. The anterior division has one sensory branch, the buccal nerve of CN V ₃ supplying the cheek.

• The posterior division is primarily sensory, with one motor branch being the nerve to mylohyoid that supplies the mylohyoid muscle and anterior belly of the digastric muscle. Other branches of the posterior division include the lingual, inferior alveolar, and auriculotemporal nerves.

• The lingual nerve unites with the chorda tympani nerve of CN VII as it passes superficial to the medial pterygoid muscle to distribute taste to the anterior two thirds of the tongue and parasympathetic innervation to the submandibular ganglion. The lingual nerve itself provides general sensation to the anterior two thirds of the tongue.

• The inferior alveolar nerve also travels superficial to the medial pterygoid muscle and proximal to its entry into the mandibular foramen. It gives rise to the nerve to mylohyoid, which travels medial to the mandible to reach its targets.

• The auriculotemporal nerve branches posteriorly from CN V ₃ and has a close anatomical relationship to the middle meningeal artery of the maxillary artery. The auriculotemporal nerve then travels posterior to the temporomandibular joint to supply the temporal region with general sensation.

CN VII is seen exiting the skull base by way of the stylomastoid foramen to supply muscles of facial expression, posterior belly of digastric, and stylohyoid.

In the neck, CNs IX, X, XI, and XII are visible, along with the sympathetic trunk, cervical plexus, and brachial plexus.

• CN IX exits the skull base at the jugular foramen.

  • It is seen in this plate following the stylopharyngeus muscle (which it supplies with motor innervation) and giving off tonsillar branches to the oropharynx, palatine tonsil, and root of the tongue.

  • It contributes sensory fibers to the pharyngeal plexus of nerves.

  • CN IX also branches to form the carotid sinus nerve that supplies the carotid sinus (baroreceptor) and carotid body (chemoreceptor).

• CN X also exits the skull base at the jugular foramen.

  • Its pharyngeal branch provides motor innervation to the pharyngeal plexus of nerves.

  • It gives rise to cervical cardiac branches that contribute to the cardiopulmonary plexus.

  • CN X gives rise to recurrent laryngeal nerves on each side that ascend in the tracheoesophageal groove and pass deep to the inferior pharyngeal constrictor, where they are renamed as inferior laryngeal nerves.

  • The inferior laryngeal nerves travel into the piriform recess of the laryngopharynx and supply most of the intrinsic muscles of the larynx (except cricothyroid, which is supplied by external branch of superior laryngeal nerve).

• CN XI exits the skull base at the jugular foramen, along with CNs IX and X. It supplies the sternocleidomastoid and then travels through the posterior cervical triangle to reach and supply the trapezius muscle.

• CN XII exits the skull base at the hypoglossal canal. It is joined by cervical nerve fibers from C1‒2, which “hitch a ride” with it for a short distance.

  • C1 and C2 fibers exit CN XII as the superior root of ansa cervicalis (motor part of cervical plexus).

  • The superior root descends on the internal and common carotid artery, where it meets the inferior root of ansa cervicalis formed by C2 and C3.

  • The ansa cervicalis provides motor innervation to most of the infrahyoid muscles, except the thyrohyoid.

  • Additional C1 fibers continue on CN XII and branch from it more anteriorly as the nerve to thyrohyoid (which also supplies geniohyoid).

  • CN XII then courses anteriorly between hyoglossus and mylohyoid to access the oral cavity and tongue, to which it provides motor innervation (except palatoglossus).

• The sympathetic trunk is located within the prevertebral fascia just posterior to the carotid sheath.

  • Two sympathetic ganglia are visible in this image, the superior and middle cervical ganglia. The superior cervical ganglion is posterior to the internal carotid artery at the level of C1‒2. The middle cervical ganglion is located at about the level of the cricoid cartilage at C6.

• The trunks of the brachial plexus are visible in the lower neck, emerging between the anterior and middle scalene muscles. The phrenic nerve is seen descending on the anterior surface of the anterior scalene muscle to reach and supply the diaphragm muscle.

The common carotid artery provides much of the blood supply to the head and neck.

• The common carotid artery travels superiorly in the carotid sheath with the internal jugular vein and vagus nerve.

• At the level of the thyroid cartilage, the common carotid artery divides into the external carotid artery (positioned more anteriorly) and the internal carotid artery (positioned more posteriorly).

The external carotid artery gives rise to a number of branches that supply the head and neck. A mnemonic device for remembering the branches is “Some Little Fat Man Stole Papa’s Only Apple.”

• Superior thyroid artery (“Some” in mnemonic) is the first branch from the external carotid artery.

  • The superior thyroid artery branches to give rise to the superior laryngeal artery, which pierces the thyrohyoid membrane (along with internal laryngeal nerve) to supply the upper larynx.

  • The superior thyroid artery then continues inferiorly to vascularize the thyroid gland.

• Lingual artery (“Little”) is the second branch from the external carotid artery. It sometimes arises from a common trunk with the facial artery. The lingual artery courses anteriorly and deep to the hyoglossus muscle to enter the oral cavity.

• Facial artery (“Fat”) is the third branch to arise from the external carotid artery.

  • It gives rise to the ascending palatine and tonsillar arteries before ascending deep to the posterior digastric and stylohyoid muscles.

  • The facial artery then travels deep to the submandibular gland, emerging onto the mandible to reach the face. It branches to form the inferior labial artery supplying the lower lip and the superior labial artery supplying the upper lip.

  • Just distal to the ala of the nose, the facial artery is renamed the angular artery, which travels toward the medial aspect of the eye.

• The maxillary artery (“Man” in mnemonic) is one of two terminal branches of the external carotid (other is superficial temporal artery).

  • The maxillary artery is divided into three segments: mandibular, pterygoid, and pterygopalatine.

  • The mandibular segment arises directly from the external carotid artery, supplying the ear (deep auricular and anterior tympanic arteries), cranial cavity (middle meningeal artery), and mandible (inferior alveolar artery, which becomes the mental artery as it emerges onto the face).

  • The pterygoid segment supplies the muscles of mastication and the cheek (buccal artery).

  • The pterygopalatine segment supplies deeper structures in the head, including the palate (descending palatine artery), nasal cavity (sphenopalatine artery), molar teeth (posterior superior alveolar artery), anterior teeth and face (infraorbital), and nasopharynx (pharyngeal artery and artery of pterygoid canal).

• The superficial temporal artery (“Stole” in mnemonic) is a terminal branch of the external carotid artery. The superficial temporal artery gives rise to a transverse facial branch before supplying the skin and superficial fascia of the temporal region.

• The posterior auricular artery (“Papa’s”) branches from the external carotid artery posteriorly to supply the external ear and scalp.

• The occipital artery (“Only”) branches from the external carotid artery posteriorly, just inferior to the posterior auricular artery. It arches superficially to the hypoglossal nerve as it courses posteriorly to supply the scalp.

• The ascending pharyngeal artery (“Apple” in mnemonic) is the only medial branch from the external carotid artery. It courses superiorly into the neck, supplying the pharynx.

The external and internal jugular veins are responsible for most of the venous drainage from the head and neck.

The external jugular vein is formed by the posterior auricular vein and posterior division of the retromandibular vein.

• The retromandibular vein is formed by the union of the superficial temporal vein and the maxillary vein.

  • The maxillary vein receives blood from the pterygoid plexus of veins surrounding the maxillary artery.

  • Note that the emissary vein of Vesalius connects the pterygoid venous plexus with the cavernous sinus, creating a path for infection in the deep face to enter the cranial cavity and potentially initiate cavernous sinus thrombosis.

• The external jugular vein travels superficial to the sternocleidomastoid muscle throughout most of its course. It pierces the investing cervical fascia at the root of the neck to drain into the subclavian vein.

The internal jugular vein begins at the skull base at the jugular foramen, where it is continuous with the sigmoid dural venous sinus.

• The internal jugular vein travels inferiorly through the neck in the carotid sheath along with the internal and common carotid arteries and vagus nerve.

• It receives blood from several branches, including the common facial vein, superior and middle thyroid veins, and occipital vein.

  • The common facial vein is formed by the union of the lingual, facial, and anterior branches of the retromandibular vein.

  • The anterior jugular vein may also drain to the common facial vein.

• The internal jugular vein joins the subclavian vein to form the brachiocephalic vein, which drains to the superior vena cava. The inferior thyroid veins drain to the brachiocephalic vein.

Lymph nodes in the head and neck are organized into superficial and deep groups, either in horizontal rings or vertical chains.

Lymph from the scalp, face, and upper neck drains to a horizontal superficial ring (sometimes called the “pericervical collar”) of lymph nodes at the junction between the head and neck, including the submental, submandibular, parotid, mastoid, and occipital nodes.

Superficial lymph from the neck drains to anterior cervical nodes that accompany the anterior jugular veins, or to the lateral cervical nodes that travel with either the external jugular vein or the accessory nerve.

A deep horizontal ring of lymphatic nodules (Waldeyer’s ring) surrounds the entrance to the gastrointestinal tract and is formed by the palatine, tubal, pharyngeal, and lingual tonsils.

All lymphatic drainage from the head and neck ultimately drains to a deep cervical chain of lymph nodes that travels with the internal jugular vein.

• This deep cervical chain is organized into superior and inferior groups of lymph nodes.

• The superior chair is located superior to the omohyoid muscle and includes the jugulodigastric (or tonsillar) node, positioned between the posterior belly of the digastric muscle and the internal jugular vein, approximately at the level of the hyoid bone.

• The inferior chain is located inferior to the omohyoid muscle and includes the juguloomohyoid node, which receives most of the lymph drainage from the tongue.

Lymph from the deep cervical chain goes to the jugular trunk, which drains to the thoracic duct on the left.

The upper image is a posterior view of the pharynx.

• Note the deep cervical chain of lymph nodes traveling with the internal jugular vein bilaterally.

• The jugulodigastric node is located superiorly, between the internal jugular vein and posterior belly of the digastric muscle, while the juguloomohyoid node is located inferiorly at the level of the omohyoid tendon.

• The pharynx is drained by retropharyngeal lymph nodes located in the buccopharyngeal fascia at the level of C1. They are frequently inflamed in the pediatric population and in infections related to the parapharyngeal space.

The lower image summarizes lymphatic drainage from the tongue.

• Lymph from the apex of the tongue drains to the submental lymph nodes.

• Lymph from the lingual body drains differently, medial to lateral, with the medial regions draining to inferior deep cervical nodes and the lateral regions to submandibular lymph nodes.

• Lymph from the root of the tongue drains to the superior part of the deep cervical chain of lymph nodes.

The thyroid gland is an endocrine gland that makes thyroid hormone and calcitonin. It is located in the neck, inferior to the thyroid cartilage and medial to the carotid sheath.

• The carotid sheath contains the common carotid artery, internal jugular vein, and vagus nerve.

The thyroid gland is composed of a right and a left lobe, connected by a narrow isthmus over the anterior surface of the second and third tracheal rings. Occasionally, a pyramidal lobe (developmental remnant of thyroglossal duct) may extend superiorly from one of the lobes.

The blood supply to the thyroid gland arises from the superior thyroid artery (from external carotid artery) and from the inferior thyroid artery (from thyrocervical trunk of subclavian artery).

Venous drainage is accomplished by the superior and middle thyroid veins, which drain to the internal jugular vein, as well as by the inferior thyroid veins, which drain to the brachiocephalic veins inferiorly.

Lymphatic drainage of the thyroid gland is by pretracheal lymph nodes, which drain to the inferior deep cervical chain of lymph nodes.

Note the close relationship of the recurrent laryngeal nerves to the thyroid gland’s lobes; the nerves ascend posterior to each lobe. Clinically, this relationship is important during thyroidectomy, to avoid iatrogenic damage to the recurrent laryngeal nerves.

The lower image correlates the surface anatomy to the position of the thyroid gland. Note that the thyroid isthmus must be retracted or divided during tracheotomy procedures.

Demonstrates a posterior view of the thyroid and parathyroid glands, their relationship to the pharynx, and their vascular supply and drainage. The pharynx narrows inferiorly at the level of C6 to form the esophagus. Note the trachea, located immediately anterior to the esophagus.

The aortic arch and superior vena cava are visible inferiorly. The right and left vagus nerves are visible on each side, coursing within the carotid sheath along with the common and internal carotid arteries and internal jugular vein.

• Each vagus nerve branches to form the superior laryngeal nerve in the carotid cervical triangle, giving rise to the internal and external laryngeal nerves.

  • The internal laryngeal nerve pierces the thyrohyoid membrane to supply the upper laryngeal lumen with sensation.

  • The external laryngeal nerve travels with the superior thyroid artery to reach its target muscle, the cricothyroid.

On the left side, the left vagus nerve gives rise to the left recurrent laryngeal nerve, which loops around the aortic arch to ascend in the tracheoesophageal groove.

• When the left recurrent laryngeal nerve reaches the inferior constrictor, it passes deep to this muscle and is renamed the inferior laryngeal nerve.

On the right side, the right vagus nerve gives rise to the right recurrent laryngeal nerve that loops around the right subclavian artery, to ascend in the tracheoesophageal groove. As on the left side, the right recurrent laryngeal nerve becomes the inferior laryngeal nerve as it passes under the inferior pharyngeal constrictor muscle.

The close anatomical relationship between the recurrent laryngeal nerves with the posterior surface of the thyroid gland has significant clinical implications during thyroidectomy.

The thyroid gland is vascularized by the superior and inferior thyroid arteries. The superior thyroid artery is the first branch from the external carotid artery, while the inferior thyroid artery arises from the thyrocervical trunk of the subclavian artery. The inferior thyroid artery is also the primary blood supply to the parathyroid glands, which can be seen posterior to the thyroid lobes.

The upper image is a posterior view of the thyroid and parathyroid glands in relation to the pharynx, carotid arterial system, and vagus nerves.

• The pharyngeal wall has been resected at the upper border of the thyroid cartilage. Note the position of the hyoid bone anteriorly and the epiglottis for orientation purposes. The thyrohyoid membrane is visible between the hyoid bone and upper border of the thyroid cartilage.

• The vagus nerve descends through the neck in close approximation to the internal and common carotid artery on each side.

  • The vagus nerve gives rise to the superior laryngeal nerve, dividing into internal and external branches.

  • The internal branch pierces through the thyrohyoid membrane to supply taste and general sensation over the epiglottis and the upper portion of the larynx.

  • The external branch courses along the superior thyroid artery to reach its target of the cricothyroid muscle.

• Inferiorly, the vagus nerve gives rise to the recurrent laryngeal nerve on each side.

  • The right recurrent laryngeal nerve loops around the right subclavian artery, while the left recurrent laryngeal nerve loops more inferiorly around the aortic arch.

  • Both recurrent laryngeal nerves ascend in the tracheoesophageal groove to reach the pharynx, traveling deep to the inferior constrictor muscle to become the inferior laryngeal nerve.

  • The inferior laryngeal nerve is a mixed nerve, providing motor innervation to most intrinsic laryngeal muscles (except cricothyroid, by external laryngeal nerve) and sensory innervation to the lower portion of the larynx.

• The thyroid gland is vascularized by the superior and inferior thyroid arteries.

  • The superior thyroid artery is the first branch from the external carotid artery, while the inferior thyroid artery arises from the thyrocervical trunk of the subclavian artery.

  • The inferior thyroid artery is also the primary blood supply to the parathyroid glands.

• The lower image shows a lateral view of the thyroid gland, with the anterior surface facing to the right.

• The upper respiratory system is represented by the larynx and trachea, with the thyroid gland retracted anteriorly to expose the parathyroid glands on the right.

• Note the inferior pharyngeal constrictor muscle blending with the muscular wall of the esophagus below.

• The common carotid artery and internal jugular vein are located posteriorly. Note the superior and middle thyroid veins draining to the internal jugular vein, while the inferior thyroid vein drains from the inferior pole of the thyroid gland to the brachiocephalic vein below.

• Two nerves are seen coursing posterior to the thyroid gland, the external laryngeal and recurrent laryngeal nerves.

The laryngeal skeleton is formed by three single and three paired cartilages, including the epiglottic, thyroid, cricoid, arytenoid, corniculate, and cuneiform.

The larynx attaches to the hyoid bone, by way of the thyrohyoid membrane uniting the superior edge of the thyroid cartilage with the hyoid bone above.

The thyroid cartilage consists of two plates, or laminae, that angle anteriorly and fuse in midline to form the laryngeal prominence; the thyroid cartilage is open to the laryngopharynx posteriorly.

The thyroid cartilage has two pairs of horns; the superior horns attach to the thyrohyoid membrane, and the inferior horns articulate with the cricoid cartilage to form the synovial cricothyroid joints.

The thyroid cartilage also serves as an attachment site for the epiglottis; the epiglottis attaches to the deep surface, where the thyroid laminae join by way of the thyroepiglottic ligament.

The cricoid cartilage is the only complete ring of cartilage in the upper airway.

• Clinically, this is important for the Sellick maneuver in airway management, which involves the application of anterior pressure to the cricoid cartilage to collapse the esophagus against the vertebral column posteriorly, in order to prevent vomiting in a patient with a full stomach.

The arytenoid cartilages articulate with the cricoid cartilage on its superior border, forming synovial joints and enabling movement of the arytenoid cartilages to abduct and adduct the vocal ligaments.

Each arytenoid cartilage has several processes that allow it to attach to neighboring structures, including the vocal process for attachment of the vocal ligament and the muscular process for attachment of intrinsic laryngeal muscles.

• Note that the vocal ligament on each side spans from the vocal process of the arytenoid cartilage to the deep surface of the thyroid cartilage just inferior to the attachment of the epiglottis.

• The vocal ligament is the upper free edge of a membrane termed the conus elasticus. The conus elasticus extends inferiorly to attach to the cricoid cartilage as the median and lateral cricothyroid ligament.

The corniculate cartilages sit atop the arytenoid cartilages to lengthen their height, whereas the cuneiform cartilages are suspended in the mucosal fold that creates the laryngeal inlet (aryepiglottic fold) and do not articulate with other laryngeal cartilages.

The interior of the laryngeal skeleton is covered by respiratory mucosa, as shown in the lower image on the left. This is a laryngoscopic view looking down into the larynx from above.

• Note the root of the tongue anteriorly, tethered to the epiglottis by the median epiglottic fold. Posteriorly, you can see the flattened esophagus that is continuous inferiorly with the laryngopharynx.

• Extending posteriorly and laterally from the epiglottis, note the vocal folds that enclose the vocal ligaments.

  • Superior to the vocal folds are the ventricular folds, or false cords, which appear pink in this image.

  • Note the aryepiglottic folds attaching from the epiglottis and extending posteriorly to create the laryngeal inlet, or entrance into the larynx.

  • Two of the smaller paired cartilages are embedded within these folds, including the more lateral cuneiform and the more medial corniculate cartilages.

Most of this plate is dedicated to mastery of the intrinsic laryngeal muscles that modulate movement of and tension on the vocal ligaments.

The upper left image is a posterior view of the larynx.

• The mucosa of the laryngopharynx has been removed to demonstrate the anatomy of two intrinsic laryngeal muscles, the arytenoid and posterior cricoarytenoid.

• For orientation on this image, first note the hyoid bone with the thyrohyoid membrane connecting it to the upper edge of the thyroid cartilage. Identify the inferior horns of the thyroid cartilage and how they articulate with the cricoid cartilage.

• In terms of mucosal anatomy on this image, note the epiglottis with the aryepiglottic folds extending posteriorly from it to create the laryngeal inlet. Embedded within the aryepiglottic folds, note the cuneiform and corniculate cartilages, or tubercles.

• The arytenoid muscle has transverse and oblique fibers that act together to adduct the arytenoid cartilages during contraction, thereby narrowing the gap between the vocal folds, known as the rima glottidis.

• The posterior cricoarytenoid muscle extends from the posterior surface of the cricoid cartilage on each side to the muscular process of the arytenoid cartilage. This muscle serves to abduct the vocal folds, or widen the rima glottidis.

The upper right image is a lateral view, with the anterior surface of the larynx facing to the right.

• For orientation, note the hyoid bone with the thyrohyoid membrane connecting it to the thyroid cartilage.

• Note the synovial joint articulation between the inferior horn of the thyroid cartilage and the cricoid cartilage below.

• The cricothyroid muscle is the highlight of this image, attaching from the anterior aspect of the cricoid cartilage to the deep surface of the thyroid cartilage. This muscle pulls the thyroid cartilage anteriorly when it contracts, thereby stretching and tensing the vocal ligaments to increase the pitch of the voice.

The middle image is a posterolateral view of the larynx, with the right side of the thyroid cartilage resecting to show the deeper lateral anatomy.

• The anterior surface of the larynx is to the right in this image. For orientation, again identify the hyoid bone ( cut in midline), along with the thyroid cartilage (also cut in midline).

• The cricoid cartilage is intact in this image, and the conus elasticus fibrous membrane is visible spanning from the thyroid cartilage to the cricoid cartilage.

• The site where the inferior horn of the thyroid cartilage (removed in this image) articulates with the cricoid cartilage is exposed and labeled.

• Deep to the thyroid lamina are two intrinsic laryngeal muscles, the lateral cricoarytenoid and thyroarytenoid.

• The lateral cricoarytenoid muscle spans from the vocal process of the arytenoid cartilage to the cricoid cartilage and is responsible for adducting the vocal folds.

• The thyroarytenoid muscle extends in parallel with the vocal folds, passing from deep surface of the thyroid cartilage to the arytenoid cartilage.

  • Because of this orientation, contraction of the thyroarytenoid muscle relaxes and reduces tension on the vocal ligament, thereby lowering the pitch of the voice.

The lower image on the right side represents a superior view looking down into the larynx from above.

• For orientation, note that the anterior surface of the larynx is at the bottom of the image.

• Identify the thyroid cartilage with its two laminae uniting anteriorly at the laryngeal prominence.

• The complete ring of cartilage formed by the cricoid is visible in this image as well. The arytenoid cartilages are visible, with each vocal process attaching to a vocal ligament that extends anteriorly to the thyroid cartilage.

• First, note the posterior cricoarytenoid muscle on the back of the cricoid cartilage; it attaches to the posterior aspect of the vocal process so that when it contracts, it abducts the vocal ligaments.

• Next, the arytenoid muscle is seen running between the arytenoid cartilages. When this muscle contracts, it brings the arytenoid cartilages together, or adducts them.

• Deep to the laminae of the thyroid cartilage, note the position of the lateral cricoarytenoid and thyroarytenoid muscles.

• The lateral cricoarytenoid attaches to the anterior surface of the muscular process of the arytenoid cartilage and thereby adducts the vocal ligaments when it contracts.

• The thyroarytenoid runs parallel but lateral to the vocal ligaments, allowing it to reduce the distance between the thyroid and arytenoid cartilages when it contracts, thereby relaxing the ligaments.

• Medial to the thyroarytenoid is a small muscle known as the vocalis, which some consider to be part of the thyroarytenoid. The vocalis muscle fine-tunes the tension on the vocal ligaments and lies within the vocal fold when the mucosa is present.

The lower image provides a coronal view through the lumen of the larynx.

• For orientation, identify the epiglottis and the section through the hyoid bone laterally. The thyroid cartilage laminae are visible inferior to the hyoid bone in gray. The cricoid cartilage can be seen inferior to the thyroid laminae, and the tracheal rings extend inferior to the cricoid cartilage.

• The mucosa of the larynx projects medially to create two sets of folds within the laryngeal lumen. The vestibular (ventricular, or false) fold is the more superior, and the vocal fold is the more inferior. Note that the vocal fold contains the vocal ligament, formed by the upper free edge of the conus elasticus, as well as the vocalis muscle.

• The presence of the vestibular and vocal folds creates compartments within the lumen of the larynx.

  • The vestibule is the space located above the level of the vestibular folds and below the laryngeal inlet.

  • The ventricle is a pouch-like space housed between the vestibular and vocal folds.

  • The rima glottidis is the narrow space between the vocal folds; the glottis is created by the vocal folds and the rima glottidis between them.

  • The infraglottic cavity lies inferior to the glottis, ending at the trachea.

It is important to have a thorough understanding of the laryngeal compartments because they receive sensory innervation from different nerves. The upper images highlight the nerves supplying the intrinsic muscles and mucosa of the larynx.

The upper left image is a lateral view of the larynx, with the anterior surface facing to the right.

• For orientation, note the position of the hyoid bone, thyrohyoid membrane, and thyroid cartilage. The cricoid cartilage is largely covered by the cricothyroid muscle in this image. The trachea is visible inferiorly.

• Posterior to the larynx, note the presence of the middle and inferior pharyngeal constrictor muscles, along with the cricopharyngeus muscle and the esophagus.

• The larynx receives its nerve supply via the vagus nerve. The vagus nerve gives rise to two branches that provide motor and sensory innervation to the larynx, the superior laryngeal and recurrent laryngeal nerves.

• The superior laryngeal nerve is a mixed nerve (with motor and sensory fibers); it branches from the vagus nerve just superior to the level of the hyoid bone and divides to form the sensory internal laryngeal nerve and the motor external laryngeal nerve.

  • The internal laryngeal nerve pierces the thyrohyoid membrane to supply the vestibule, vestibular folds, ventricle, and upper surface of the vocal folds with sensory innervation.

  • The external laryngeal nerve courses inferiorly along the inferior pharyngeal constrictor muscle to reach and supply the cricothyroid muscle with motor innervation.

• The recurrent laryngeal nerve is also a mixed motor and sensory nerve that branches from the vagus nerve more inferiorly.

  • On the right, the recurrent laryngeal nerve branches around the right subclavian artery, while on the left, it loops around the aortic arch, posterior to ligamentum arteriosum.

• The recurrent laryngeal nerves then ascend in the tracheoesophageal groove until they reach the lower border of the inferior constrictor muscle, where they undergo a name change to the inferior laryngeal nerve.

The upper right image has the hyoid bone removed and the right thyroid lamina resected. The cricoid cartilage is intact. This view well demonstrates the lateral cricoarytenoid and thyroarytenoid muscles deep to the thyroid lamina.

• The internal laryngeal nerve is seen providing sensory branches to the upper mucosa of the larynx.

• The inferior laryngeal nerve courses anteriorly to supply all the intrinsic laryngeal muscles (except cricothyroid, supplied by external laryngeal nerve). The inferior laryngeal nerve also carries sensory fibers from the laryngeal mucosa on the inferior surface of the vocal folds and infraglottic cavity.

Elucidates the action of each of the intrinsic laryngeal muscles.

The upper image represents a lateral view of the larynx, with its anterior surface facing to the right.

• Note the thyroid cartilage superiorly, the cricoid cartilage inferiorly, and the arytenoid cartilages sitting atop the posterior aspect of the cricoid cartilage.

• The vocal ligament is visible in hatched lines extending from the anteriorly positioned vocal process of the arytenoid cartilage to the deep surface of the thyroid cartilage.

• The cricothyroid muscle attaches from the cricoid cartilage to the thyroid cartilage, without touching the arytenoid cartilages.

  • The cricothyroid decreases the distance between the anterior thyroid cartilage and anterior arch of the cricoid cartilage, thereby stretching the vocal ligaments.

The middle left image is a superior view, with the anterior surface of the larynx at the bottom of the figure.

• Contraction of the posterior cricoarytenoid muscle is shown on each side, pulling the muscular process of the arytenoid cartilage posteriorly.

• This action swings the vocal process of each arytenoid cartilage laterally, thereby abducting the vocal ligaments.

The middle right image shows the antagonist to the posterior cricoarytenoid, the lateral cricoarytenoid.

• When the lateral cricoarytenoid muscle contracts, it pulls the muscular process of the arytenoid cartilage anteriorly, thereby moving the vocal process medially to adduct the vocal ligaments.

On the lower left image, the arytenoid muscles are highlighted, spanning the arytenoid cartilages. When arytenoid muscles contract, they adduct the arytenoid cartilages and thus the vocal ligaments as well.

The lower right image highlights the actions of the thyroarytenoid and vocalis muscles, which serve to bring the arytenoid cartilages and the thyroid cartilages closer together.

The upper image demonstrates the anatomy of the eye and eyelids (palpebrae) in situ.

• The deep surface of the upper and lower eyelids is lined with a serous membrane known as the palpebral conjunctiva. Bulbar conjunctiva reflects onto the sclera or white of the eye. Palpebral and bulbar conjunctivae are continuous with one another at the conjunctival fornix. The conjunctiva allows the eyelids to move over the eyeball without friction.

• The deep surface of each eyelid contains oil-secreting tarsal glands that prevent the eyelids from adhering to one another.

  • On the medial aspect of each eyelid, note the presence of a small hole, or punctum, on a little hill, or lacrimal papilla.

  • The puncta collect tears and funnel them medially and inferiorly toward the lacrimal sac on each side.

  • Tears are collected at the medial corner of the eye in a region known as the lacrimal lake ; a swelling (lacrimal caruncle) is present within the lacrimal lake to direct tears either superiorly or inferiorly toward the appropriate punctum.

The middle image represents a sagittal section through the eye and eyelids. The anterior surface of the eyelids is directed to the left on this image. The frontal bone is visible in section superiorly, while the maxilla is seen inferiorly.

• Each eyelid is formed by a connective tissue core, known as a tarsal plate, or tarsus.

• Tarsal glands invest each tarsus to secrete an oily substance that lubricates the eyelids.

  • Tarsal glands are distinct from sebaceous glands associated with the cilia, or eyelashes. Both types of glands can be inflamed or infected, resulting in a chalazion for the tarsal glands or a stye for the ciliary glands.

• Each tarsus is invested by the palpebral portion of the orbicularis oculi superficially and by the palpebral conjunctiva on the deep surface.

  • Note the continuity of the conjunctiva as it lines each eyelid, turns posteriorly at the fornix, then covers the sclera of the eye. When inserted into the eye, contact lenses are placed into the conjunctival sac between the palpebral and bulbar conjunctivae.

• The superior eyelid is elevated by two muscles, the skeletal muscle known as the levator palpebrae superioris and the smooth superior tarsal muscle. Both skeletal and smooth muscles are used to elevate the upper eyelid to ensure that tonic support is provided by the tarsal muscle when the skeletal muscle fatigues.

• The anatomy of the eye itself is also highlighted in this image, showing the outer tunic, or layer, of the eye formed by the cornea anteriorly and the sclera posteriorly.

  • The iris with its pupillary opening is seen posterior to the cornea.

  • The lens lies just posterior to the pupil and helps to focus light on the retina.

  • The eye contains two chambers anterior to the lens; the anterior chamber lies in front of the iris, and the posterior chamber lies between the iris and lens. A watery secretion known as aqueous humor circulates through the anterior and posterior chambers.

The lower image demonstrates each tarsus and its connections with the surrounding facial skeleton.

• Both tarsi are connected to the orbital rim by the orbital septum, which is continuous with the periosteum of the skull.

• The tarsi are reinforced medially and laterally by palpebral ligaments. The lacrimal sac responsible for collecting tears can be seen just deep to the medial palpebral ligament.

Tears are continuously secreted from the lacrimal gland, which is innervated by the facial nerve parasympathetics, and are dispersed across the conjunctiva and cornea of the eyeball by the action of blinking eyelids.

The tears flow from about 12 small lacrimal ducts diagonally across the eyeball and are collected medially in the lacrimal lake, which is drained by two lacrimal canaliculi.

The openings of the canaliculi are visible as two small lacrimal punta at the medial margins of the upper and lower eyelids.

Once drained, the tears collect in the lacrimal sac and then are squeezed into the nasolacrimal duct by the blinking action of the eyelids.

The nasolacrimal duct opens into the inferior nasal meatus beneath the inferior nasal turbinate. Therefore, when the lacrimal system is flooded by tears, as in crying or from irritation to the eye, the increased tear production ultimately collects in the nasal cavity, causing sniffling, and any excess tears may cascade over the lower eyelid and run down the cheek.

Tears are composed of a plasma ultrafiltrate that keeps the cornea moist and allows oxygen to diffuse through the tear film to reach the corneal epithelium, which is avascular. The tears, with contributions from accessory lacrimal glands, the tarsal glands of the eyelids, and goblet cells of in the conjunctiva, contain albumins, lactoferrin, lysozyme, lipids, and electrolytes. Therefore, tears not only moisten the conjunctiva and cornea, but also combat infection and help wash dust and other foreign material from the surface of the eye.

There are six extrinsic muscles of the eye (extraocular muscles), including the four rectus muscles (superior, inferior, medial, and lateral) and two oblique muscles (superior and inferior).

The upper image represents a lateral view of the right orbit, with the lateral orbital wall removed. Note the position of the optic nerve exiting the posterior pole of the eye.

• Surrounding the optic nerve is the common tendinous ring of Zinn, from which the rectus muscles originate posteriorly.

• Starting superiorly, note the levator palpebrae superioris, which elevates the upper eyelid and does not act on the eyeball itself.

• The superior oblique muscle courses anteriorly to change its angle of pull at the connective tissue trochlea on the superomedial aspect of the bony orbit. The tendon of the superior oblique muscle then turns to attach to the posterior aspect of the eyeball, with its tendon inserting inferior to the superior rectus muscle.

• The medial and lateral rectus muscles flank the optic nerve. The lateral rectus has been resected here to show the deeper-lying optic nerve and medial rectus muscle.

• The inferior oblique muscle passes transversely across the floor of the orbit, inserting into the posterior aspect of the eye, and passes inferior to the tendon of the inferior rectus muscle.

The middle image represents a superior view, with the orbital plate of the frontal bone removed. The medial wall of the orbit is to the left and the lateral wall to the right.

• Note the levator palpebrae superioris attaching to the superior tarsus. Just inferior to the levator, the superior rectus muscle has been resected in part to reveal deeper structures, such as the optic nerve and inferior rectus. Note the medial and lateral rectus muscles, which act to adduct and abduct the eye, respectively.

• The superior oblique muscle is visible from this view, with its muscle belly lying superior to that of the medial rectus. The superior oblique sends its tendon through a connective tissue pulley known as the trochlea to change its angle of pull on the eye.

The lower image summarizes the cranial nerve innervation of each of the intrinsic eye muscles. Several “chemical” mnemonic devices can also help.

• The superior oblique muscle is innervated by cranial nerve (CN) IV (if you are a chemist, the designation for sulfate, SO ₄ , may help you remember this innervation pattern).

• The lateral rectus is innervated by CN VI (“LR ₆ ,” even though this is not a valid chemical designation).

• All the rest (AR) of the extrinsic eye muscles, including the levator palpebrae superioris, are innervated by CN III (“AR ₃ ”).

The upper image is a superior view looking down into the orbit from above, with the orbital plate of the frontal bone removed. For orientation, note the position of the cribriform plate of the ethmoid bone and the crista galli in midline. Note the entry of the optic nerves into the optic canal just distal to the optic chiasm.

• Cranial nerves (CNs) III, IV, V, and VI play a key role in innervating orbital structures. After exiting the brain stem, these nerves travel in close relation to the cavernous dural venous sinus (see in blue ) deep to them. CNs III, IV, V ₁ , and V ₂ travel through the lateral dural wall of the sinus, while CN VI travels through the sinus itself, immediately adjacent to the internal carotid artery.

• CN IV is seen entering the orbit via the superior orbital fissure and quickly innervating its muscular target, the superior oblique muscle.

• CN V is seen crossing over the petrous ridge of the temporal bone. It expands to form the trigeminal sensory ganglion and then divides into CNs V ₁ , V ₂ , and V ₃ .

• CN V ₁ , the ophthalmic division of the trigeminal nerve, enters the orbit via the superior orbital fissure before dividing into three branches: nasociliary, frontal, and lacrimal (“NFL”).

• The frontal nerve travels superior to the levator palpebrae superioris. It divides into the more medial supratrochlear nerve (so named because it travels superior to trochlea of superior oblique muscle) and the supraorbital nerve. The supraorbital nerve enters the forehead via the supraorbital foramen or notch.

• The lacrimal nerve travels laterally toward the lacrimal gland and picks up parasympathetic fibers from CN VII that “hitchhike” along its distal portion to reach the lacrimal gland. (These “acquired” fibers are distinguished from the “resident” fibers of the lacrimal nerve.)

• The nasociliary nerve is seen medially on the upper image, traveling medially. Its course is elucidated in the lower image.

The lower image is also a superior view, but with several muscles resected (levator palpebrae superioris, superior rectus, superior oblique).

• • CN II is visible extending posteriorly from the eyeball, conveying the special sense of sight.

  • The branching pattern of CN III is well demonstrated in this image. Note that the oculomotor nerve divides into a superior and an inferior division shortly after entering the orbit. The superior division supplies the levator palpebrae superioris and superior rectus, while the inferior division supplies the inferior rectus, medial rectus, and inferior oblique muscles.

  • The ciliary ganglion is a parasympathetic ganglion associated with CN III. Note that the inferior division of CN III carries presynaptic parasympathetic branches into the ciliary ganglion. They synapse in the ganglion before traveling on short ciliary nerves to reach their smooth muscular targets in the eye (ciliaris and sphincter pupillae).

  • This view better demonstrates the course of the nasociliary nerve of CN V ₁ .

  • Note that this nerve gives rise to sensory roots that pass through the parasympathetic ciliary ganglion without synapsing, emerging from it as short ciliary nerves that enter the posterior aspect of the eyeball.

  • The nasociliary nerve also gives rise directly to long ciliary nerves that supply the eyeball as well. The nasociliary nerve then continues medially and anteriorly, giving rise to posterior ethmoidal nerves. Finally, the nasociliary nerve terminates as the anterior ethmoidal and infratrochlear nerves.

• CN VI is seen traveling lateral to the inferior division of CN III and branching to innervate the lateral rectus muscle.

The upper image is a superior view of the orbit. For orientation, identify the eyes, nose, and teeth at the bottom of the image. On the right side, the skin of the forehead is partially intact, with the underlying frontalis muscle. On the left side, this muscle has been removed, along with the orbital plate of the frontal bone, to show the orbital contents, including the lacrimal gland.

• The nerves of the orbit are the focal point of this image, including cranial nerve II, CN III, CN IV, ophthalmic division (V ₁ ) of CN V, and CN VI.

• Begin your examination posteriorly, at the trigeminal ganglion. Note the ophthalmic division of CN V entering the orbit via the superior orbital fissure. Within the orbit, V ₁ branches into three nerves, the nasociliary, frontal, and lacrimal (“NFL”).

  • The frontal nerve is the largest of the branches and courses superior to the levator palpebrae superioris muscle. The frontal nerve branches into the supraorbital and supratrochlear nerves.

  • The lacrimal nerve, the most lateral of the branches, travels to the lacrimal gland and the neighboring and overlying skin.

  • The nasociliary nerve is the most medial branch and gives rise to long and short ciliary nerves, anterior and posterior ethmoidal nerves, and ultimately the infratrochlear nerve.

The lower image is an anterior view of the orbit. For orientation, the right orbit is illustrated, with the lateral wall to the left and the medial wall to the right. The ghosted (transparent) globe of the eye allows a better appreciation of the course of the extraocular muscles and nerve.

• Begin your examination with the extraocular muscles.

  • First, identify the lateral rectus, innervated by CN VI on its deep surface.

  • Next, note the medial rectus, which has been cut in this image.

  • The superior and inferior rectus muscles are readily visible. The inferior division of CN III can be seen innervating the inferior rectus. The superior oblique muscle is seen coursing horizontally to reach its trochlea medially, while the inferior oblique is visible inferior to the inferior rectus.

• In terms of neural elements, first note the optic nerve entering the orbit through the optic canal. CNs III, IV, V ₁ , and VI enter the orbit via the superior orbital fissure.

• Note the terminal branches of the frontal nerve of CN V ₁ emerging onto the forehead as the supraorbital and supratrochlear nerves.

  • The lacrimal nerve is visible coursing laterally through the orbit.

  • Several branches of the nasociliary nerve are also visible, including the long and short ciliary nerves and the infratrochlear nerve.

• Inferiorly, in the floor of the orbit, note the infraorbital nerve of CN V ₂ .

  • Identify the zygomatic nerve of CN V ₂ as it courses laterally to give rise to the zygomaticofacial and zygomaticotemporal nerves on the face.

  • The zygomaticotemporal nerve also exhibits a communicating branch to the lacrimal nerve of CN V ₁ .

The upper image shows a superior view of the arteries of the right orbit, with the orbital plate of the frontal bone removed. The medial wall of the orbit is to the left and the lateral wall to the right. Note the presence of the lacrimal gland on the lateral side.

• The ophthalmic artery provides most of the blood supply to structures within the orbit and is a branch of the internal carotid artery. The ophthalmic supplies the eye itself, along with the lacrimal gland and extraocular muscles. Its branches also continue onto the forehead to supply the skin there.

• The ophthalmic artery gives rise to the central artery of the retina, which pierces the dural sheath of the optic nerve to enter the eye at the optic disc.

• Its terminal branches are end arteries and provide the sole blood supply to the retina.

• The ophthalmic artery then gives rise to a lacrimal artery and several posterior ciliary arteries that pierce the sclera posteriorly to supply the outer layers of the eye. Note that the lacrimal artery supplies the lateral palpebral artery that will vascularize the eyelid superficially.

• The ophthalmic artery then continues medially and gives rise to the supraorbital artery.

• The ophthalmic artery gives off several posterior and anterior ethmoidal arteries that supply the ethmoidal air cells and nasal cavity before terminally branching into the supratrochlear and dorsal nasal arteries. The supratrochlear artery provides a medial palpebral artery that will supply the eyelid superficially.

The middle image demonstrates an anterior view of the vasculature of the orbital rim and eyelids. Note that the nose is located to the right on this image (medial side of the orbit), and the lateral wall of the orbital rim is to the left.

• This region has a number of sites of anastomosis between branches of the internal carotid and external carotid artery, marked by “X”.

• Recall that the ophthalmic artery gives rise to the supraorbital and supratrochlear arteries on the forehead and the dorsal nasal artery on the bridge of the nose.

• The external carotid artery gives rise to several branches in this region as well.

  • The superficial temporal artery anastomoses with the supraorbital artery.

  • The angular artery (from the facial artery) anastomoses with the supratrochlear artery.

  • The medial and lateral palpebral arteries divide to supply the upper and lower eyelids, forming an arterial arch on each eyelid through their anastomoses.

  • Branches from the superficial temporal artery anastomose with these palpebral arteries superiorly and inferiorly.

The lower image demonstrates the relationship of the ophthalmic veins with tributaries on the face and in the cranial cavity.

• The superior ophthalmic vein drains into the cavernous dural venous sinus in the cranial vault, while the inferior ophthalmic vein communicates with the pterygoid venous plexus in the infratemporal fossa.

• Both ophthalmic veins receive venous blood from the face through the supraorbital and angular veins. These communications provide a potential path for infectious agents to travel from the face to the cavernous sinus and result in thrombosis.

Represents a cross (horizontal) section through the eyeball and optic nerve.

Note that the optic nerve is enclosed by a meningeal capsule and subarachnoid space. This is clinically relevant because elevated intracranial pressure transmits to the optic nerve, creating papilledema, or a choked disc, where blurring of the margins of the optic disc occurs.

The eyeball is enclosed by a fascial sheath known as Tenon’s capsule. Note where the medial and lateral rectus muscles pierce this capsule.

Deep to this fascial sheath, three layers, or tunics, make up the walls of the eyeball: fibrous outer layer, vascular middle layer, and inner layer.

The outer tunic of the eye is formed by the sclera and the cornea.

• The sclera forms “the white of the eye” and can be seen through the transparent bulbar conjunctiva.

• The sclera ends anteriorly at the corneal limbus, where the cornea begins. The cornea is transparent and is the first of the refractive media that focus light on the retina.

• The cornea is completely avascular, relying on neighboring capillary beds and fluids (lacrimal fluid and aqueous humor) for its nutritional needs.

The middle tunic of the eye is highly vascular and is formed by the choroid, ciliary body, and iris.

• The choroid layer is located between the sclera and retina. Anteriorly, the choroid expands to form the ciliary body.

• The ciliary body provides attachment for the lens of the eye through the zonular fibers.

  • The smooth ciliary muscle within the ciliary body contracts to slacken the zonular fibers; when it relaxes, the fibers become tense.

  • Slack zonular fibers result in a more rounded or convex lens, which is necessary for near vision. Taut zonular fibers result in a less convex or relatively flattened lens, necessary for far vision.

  • Ciliary processes of the ciliary body synthesize aqueous humor, which is the fluid that circulates through the posterior chamber, pupil, and into the anterior chamber. Aqueous humor is taken up through the scleral venous sinus, or canal of Schlemm. Blockage of this canal is one way by which intraocular pressure may increase (as in glaucoma).

• The ciliary body extends anteriorly as the iris, which is a contractile diaphragm that regulates the amount of light entering the eye. It consists of two smooth muscles that regulate light input: sphincter pupillae (under parasympathetic control) and dilator pupillae (under sympathetic control).

The inner tunic of the eye is the retina.

• The retina consists of two parts, including the optic, or visual, part that is light sensitive, located posterior to the ora serrata, and the nonvisual part, or ciliary part of the retina.

• In the posterior aspect of the retina, close to the optic nerve, there are two areas of specialization for the visual retina.

  • The optic disc is where the ganglion cell axons along with the central artery and vein of the retina enter the interior of the eye; this area lacks photoreceptors and is the anatomical “blind spot” of the eye.

  • Just lateral to the optic disc is a “yellow spot,” the macula lutea , which contains a depressed fovea centralis. The fovea is the site for the most acute vision.

When light enters the eye, it first passes through the cornea, aqueous humor of anterior chamber, and lens. It then must pass through the vitreous body, which fills much of the interior of the eyeball.

• In addition to serving as a refractive medium, the vitreous also provides physical support to the retina and lens.

• The hyaloid canal can be seen coursing through the central region of the vitreous body. The hyaloid canal is a developmental leftover that extends from the optic nerve to the lens; in the embryo, it transmits vasculature that supplies the lens.

Focuses on the anterior segment of the eye, including the cornea, anterior chamber, iris, ciliary body, lens, and posterior chamber.

The cornea forms the outermost layer of the anterior chamber.

• The cornea is avascular, receiving nutrition from lacrimal fluid and aqueous humor.

• It is lined on its deep surface by the endothelium of the anterior chamber, which is critical in maintaining the health and clarity of the corneal stroma.

• It also is responsible for regenerating Descemet’s basement membrane, which serves as a protective barrier against infection and trauma. Inflammation of the anterior segment may result in Descemet membrane folds clinically.

• Schwalbe’s line marks the end of Descemet’s membrane and the site where the trabecular meshwork anchors into the peripheral edge of the cornea.

Aqueous humor is synthesized by the ciliary processes of the ciliary body.

• Aqueous humor circulates into the posterior chamber, through the pupil, and into the anterior chamber.

• It travels through the trabecular meshwork and spaces of the iridocorneal angle (spaces of Fontana) before being resorbed by the venous system via the scleral venous sinus (canal of Schlemm).

• This sinus is located at the sclerocorneal junction, anterior to a projection known as the scleral spur.

The ciliary body also contains the ciliary muscle, responsible for regulating tension on the lens.

• When the ciliary muscle contracts under parasympathetic control (from CN III), it slackens the tension on zonular fibers, and the lens rounds up for near vision through the process of accommodation.

• When ciliary muscle relaxes, it pulls the zonular fibers out and flattens the lens for far vision.

The anatomy of the iris is also highlighted in cross section in this plate, with its circularly arranged sphincter pupillae and longitudinal dilator pupillae smooth muscle fibers.

The upper image reveals the deep surface of the anterior segment of the eye, including structures positioned anterior to the vitreous body.

First, note the position of the ora serrata, which divides the optic, or visual, part of the retina from the nonvisual, ciliary part of the retina. The choroid is located superficial to the retina, with the sclera most superficial.

The lens is a transparent, biconvex structure that consists of an outer elastic capsule into which zonular fibers insert to regulate its shape. In the lower image, the ciliary processes, from which the zonular fibers arise, are visible peripheral to the lens.

In the middle image to the right, note the more detailed anatomy of the lens. Its capsule is thickest near the equator and thinnest at its posterior pole. This is clinically relevant because the thin nature of the posterior lens capsule makes it vulnerable to tearing during cataract surgery.

The upper image outlines the blood supply and venous drainage to the eyeball. The lower image shows the funduscopic (ophthalmoscopic) view of the retinal vasculature.

The arterial supply to the eye originates from the ophthalmic artery, which gives rise to retinal blood vessels (from central artery of retina) and choroidal blood vessels (supplying choriocapillaris or capillary lamina of choroid). The main branches from the ophthalmic artery are the central artery of the retina, long and posterior ciliary arteries, and muscular branches that give rise to anterior ciliary arteries.

The central artery of the retina branches from the internal carotid artery inferior to the optic nerve and pierces the dural sheath of the optic nerve about 8 to 15 mm posterior to the globe of the eye.

• The central artery enters the retina at the optic disc and divides into superior and inferior branches, which further divide into temporal and nasal end arteries supplying internal retinal regions corresponding to each quadrant of the visual field.

• The central artery also supplies the macula (region of highest visual acuity). Because its terminal branches are end arteries, they lack substantive anastomosis and are rendered susceptible to embolic events, such as central retinal artery occlusion, which presents as acute, painless loss of vision in one eye.

The external surface of the retina is supplied by the ciliary arteries that form the choriocapillaris.

• The numerous short posterior ciliary arteries arise from the ophthalmic artery as it crosses the optic nerve and directly supply the choroid and the outer, nonvisual retina.

• The two long posterior ciliary arteries pierce the sclera to travel between the sclera and choroid and anastomose with the anterior ciliary arteries, which are direct continuations of muscular branches to the extraocular muscles.

Venous drainage of the eye occurs by the central vein of the retina and the vorticose veins.

• The central vein of the retina typically drains to the cavernous sinus.

• The vorticose veins drain the choroid layer and then join the superior or inferior ophthalmic veins. The ophthalmic veins in turn drain to the cavernous sinus (superior ophthalmic vein) or the pterygoid venous plexus (inferior ophthalmic vein).

In the lower image, note the position of the optic disc, where branches of the central artery and vein enter the retina, along with their end-arterial branches that correspond to each quadrant of the retina. The fovea centralis, with its centrally located macula, is visible in this funduscopic view just lateral to the optic disc. The macula may receive branches from the central artery.

Shows a three-dimensional representation of the vascular supply of the choroid layer of the eyeball.

The arterial supply to the choroid layer of the eye originates from the ophthalmic artery, which gives rise to choroidal blood vessels (supplying choriocapillaris, or capillary lamina of choroid).

• • The main branches from the ophthalmic artery are the central artery of the retina, long and posterior ciliary arteries, and muscular branches that give rise to anterior ciliary arteries.

The external surface of the retina is supplied by the ciliary arteries that form the choriocapillaris.

• The numerous short posterior ciliary arteries arise from the ophthalmic artery as it crosses the optic nerve; they directly supply the choroid and the outer, nonvisual retina.

• The two long posterior ciliary arteries pierce the sclera to travel between the sclera and choroid; they anastomose with the anterior ciliary arteries, which are direct continuations of muscular branches to the extraocular muscles.

Venous drainage of the choroid layer of the eye occurs by the vorticose veins.

• • The vorticose veins drain the choroid layer and then join the superior or inferior ophthalmic veins.

  • The ophthalmic veins in turn drain to the cavernous sinus (superior ophthalmic vein) or the pterygoid venous plexus (inferior ophthalmic vein).

The upper image represents a coronal, or frontal, section through the temporal bone to demonstrate the pathway for sound reception.

• Sound waves are collected by the external ear, or auricle, and funneled into the external acoustic meatus, where they strike the tympanic membrane.

• Movement of the tympanic membrane translates sound waves into mechanical energy by way of the middle ear ossicles, including the malleus, incus, and stapes.

• The malleus attaches to the deep surface of the tympanic membrane so that movement of the membrane results in movement of the malleus.

• The malleus articulates with the incus and sets it in motion, while the incus articulates with the stapes and results in its movement.

• The base of the stapes rests in the oval window, which communicates with the inner ear; this is where movement of the middle ear ossicles is transformed to hydraulic energy in the membranous labyrinth of the cochlea.

• The bony labyrinth of the cochlea has the appearance of a snail’s shell; it contains a membranous cochlear duct that has endolymph and houses the sensory receptors for hearing.

• The cochlear duct is suspended in perilymph fluid, which is set into motion by the movement of the stapes at the oval window.

• The cochlear division of CN VIII innervates the spiral organ of Corti, within the cochlear duct.

• Perilymph in the scala vestibuli courses distally through the turns of the cochlea until it reaches the helicotrema, where it then passes through the scala tympani to reach the round window, where the perilymph fluid waves are dissipated.

In addition to showing the path for sound transduction, the upper image also demonstrates the boundaries of the middle ear cavity.

• Superiorly, its roof is formed by the tegmen tympani, separating the middle ear from the middle cranial fossa.

• Inferiorly, its floor is formed by a thin layer of bone overlying the internal jugular vein.

• Laterally, the tympanic membrane encloses the middle ear, or tympanic cavity.

• Medially, the promontory, along with the oval and round windows, characterizes the middle ear and separates it from the internal ear.

• Anteriorly, note the opening of the pharyngotympanic tube into the middle ear. This tube courses inferiorly in adults and more horizontally in children to reach the nasopharynx (shown in the lower figures). The short, horizontal nature of the pharyngotympanic tube in the child makes transmission of pathogens from the pharynx more likely to enter and infect the middle ear.

The upper left image shows a lateral view of the external ear, or auricle.

• The auricle consists of a core of elastic cartilage covered by thin skin.

• The outer margin of the auricle is defined by the helix, which is continuous inferiorly with the lobule.

• Note the antihelix located more anteriorly and closer to the external acoustic meatus.

• Superiorly, the antihelix splits into two little legs, or crura, and inferiorly, it is continuous with the antitragus.

• The tragus lies medial to the antitragus and is a small, tongue-like extension partially covering the external acoustic meatus.

The upper right image reveals the anatomy of the lateral side of the tympanic membrane, as would be viewed through an otoscope clinically.

• The tympanic membrane separates the external acoustic meatus from the middle ear, or tympanic cavity. It is concave facing the external acoustic meatus (bends in).

• The malleus is visible through the tympanic membrane, with its lateral process visible superiorly, connecting to the handle and terminating inferiorly as the umbo. From the umbo, the cone of light is reflected from the otoscope’s light source.

• Superior to the handle of the malleus, note the pars flaccida of the tympanic membrane; this region is more loosely organized and more fragile than the pars tensa, which lies inferior to the lateral process of the malleus and makes up most of the tympanic membrane.

The middle image represents an oblique section through the temporal bone, with the anterior side oriented to the right and the posterior side to the left.

• For orientation, identify the external acoustic meatus, leading to the tympanic membrane.

• The malleus, incus, and stapes are visible in the tympanic cavity.

• Note the tensor tympani muscle attaching from the handle of the malleus to the wall of the pharyngotympanic tube anteriorly. This muscle acts to dampen the movement of the malleus; it is innervated by cranial nerve (CN) V ₃ . (A mnemonic device for remembering this is that tiny tensors are supplied by the trigeminal nerve, with the other tensor being the tensor veli palatini.)

The lower left image demonstrates the anatomy of the lateral aspect of the tympanic cavity with the tympanic membrane removed.

• For orientation, note the lateral process and handle of the malleus.

• The chorda tympani branch of CN VII is visible emerging from behind the neck of the malleus.

• The body of the incus articulates with the malleus, and its long limb articulates with the head of the stapes.

• Note the attachment of the stapedius muscle from the neck of the stapes to the pyramidal eminence on the posterior wall of the tympanic cavity. The stapedius muscle is innervated by CN VII.

• The lower right image summarizes the synovial articulations between the middle ear ossicles.

• The malleus is shaped like a hammer, and its head articulates with the incus.

• The incus is configured like an anvil, with its body articulating with the malleus.

• The incus extends a long limb that terminates as the lenticular process, which articulates with the head of the stapes (shaped like a stirrup).

• The base, or footplate, of the stapes sits in the oval window on the medial wall of the tympanic cavity.

The upper image represents a sagittal section through the temporal bone at the level of the tympanic cavity.

• The anterior side of the image is directed to the left; note the pharyngotympanic tube extending anteriorly and inferiorly toward the nasopharynx.

• Posteriorly, the tympanic cavity communicates with the air cells of the mastoid process by way of the mastoid antrum. In addition, the posterior wall of the tympanic cavity is closely associated with the facial nerve descending in the facial canal. The facial canal terminates inferiorly as the stylomastoid foramen.

• The internal surface of the tympanic membrane is visible, attached to the handle of the malleus. The tensor tympani muscle is visible attaching from the wall of the pharyngotympanic tube to the handle of the malleus.

• The incus, with its head articulating with the head of the malleus, extends its long limb to terminate as the lenticular process, which articulates with the stapes (not shown in this image). The chorda tympani nerve of CN VII is seen coursing between the long limb of the incus and the neck of the malleus.

The lower image represents a sagittal section through the temporal bone, looking at the medial wall of the tympanic cavity.

• In this image the anterior side is to the right (note position of tensor tympani muscle) and the posterior side to the left (note mastoid antrum and air cells).

• The stapes is visible, with its footplate in the oval window on the medial wall of the tympanic cavity. The stapedius muscle is seen extending from the pyramidal eminence of the posterior tympanic wall to the neck of the stapes; it acts to dampen the movement of the stapes.

• The course of the facial nerve is well demonstrated in this image.

  • Note the ghosted geniculate ganglion (sensory ganglion of CN VII) at the top of the image. At the level of the geniculate ganglion, the facial nerve branches to form the parasympathetic greater petrosal nerve; this nerve ultimately synapses in the pterygopalatine ganglion to supply the lacrimal gland and the nasal and palatal mucosal glands.

  • The main trunk of the facial nerve proceeds inferiorly in the facial canal, giving rise to the nerve to stapedius and chorda tympani along its descent to the stylomastoid foramen.

• The parasympathetic lesser petrosal nerve of cranial nerve (CN) IX is seen medial to the greater petrosal nerve of CN VII in the floor of the middle cranial fossa.

  • Shortly after its exit from the skull base via the jugular foramen, CN IX gives rise to the tympanic nerve, which reenters the skull base at the tympanic canaliculus.

  • The tympanic nerve forms the tympanic plexus over the promontory of the middle ear, along with sympathetic contributions from the superior cervical ganglion.

  • Sensory fibers from this plexus remain in the middle ear, while the parasympathetic fibers exit as the lesser petrosal nerve.

  • The lesser petrosal nerve exits the middle cranial fossa via the foramen ovale to reach the otic ganglion, where it synapses. These parasympathetic fibers supply the parotid gland.

• The relationship of the internal carotid artery and its carotid canal with the anterior wall of the tympanic cavity is visible in this image. Note how the internal carotid artery approaches the inferior opening of the carotid canal at the skull base vertically. The carotid canal then takes a horizontal turn anteriorly to open into the middle cranial fossa.

• The blood supply to the middle ear cavity is clearly depicted in this view as well.

  • First, identify the external carotid artery, with the maxillary artery as one of its terminal branches. From the mandibular segment of the maxillary artery, note the deep auricular artery and anterior tympanic artery.

  • The ascending pharyngeal artery from the external carotid gives rise to the inferior tympanic artery, which anastomoses with the caroticotympanic artery from the internal carotid artery.

The inner ear contains the sensory organs for hearing and balance and is innervated by cranial nerve (CN) VIII.

• The inner ear is housed within the petrous portion of the temporal bone, medial to the middle ear cavity. It consists of an outer bony labyrinth that is hollow.

• The bony labyrinth contains the membranous labyrinth, a series of interconnected membranous tubes that house the sensory receptors for hearing and balance.

• The membranous labyrinth is suspended in a fluid known as perilymph and contains a fluid known as endolymph.

The upper images represent the anatomy of the bony labyrinth. It consists of the cochlea, vestibule, and semicircular canals.

• The cochlea is shaped like a conch seashell, with 2.5 turns around its bony core, or modiolus.

  • The cochlea contains the round window and also communicates with the vestibule laterally at the oval window, where the footplate of the stapes sits.

  • From the oval window, note the bony channel known as the scala vestibuli.

  • This bony channel is continuous with the scala tympani at the helicotrema; the scala tympani terminates at the round window of the cochlea.

• The vestibule is a small, round chamber that communicates with the cochlea anteriorly and the semicircular canals posteriorly. It also communicates with the posterior cranial fossa via the vestibular aqueduct, which contains the endolymphatic duct.

• Three semicircular canals extend from the vestibule: anterior, lateral, and posterior. These canals are oriented at right angles to one another.

The lower image shows the membranous labyrinth of the inner ear, with the branches of CN VIII supplying each component. The membranous labyrinth is suspended within the bony labyrinth by perilymph; the membranous labyrinth itself contains endolymph.

• • Within the cochlea, the membranous labyrinth is formed by the cochlear duct, while the vestibule contains a membranous utricle and saccule. Finally, the semicircular ducts lie within the semicircular canals.

  • The semicircular ducts communicate with the utricle, which opens into the saccule. The saccule communicates with the cochlear duct.

  • Each semicircular duct displays an ampulla that contains sensory receptors for balance.

The upper image blends the anatomy of the bony and membranous labyrinths into a single schematic figure.

• For orientation, note the position of the external acoustic meatus at the lower left margin of the image. The tympanic membrane can be seen with the malleus attaching to it.

  • The malleus articulates with the incus, which articulates with the stapes. The stapes sits in the oval window that opens into the bony labyrinth of the vestibule.

  • The vestibule contains two membranous labyrinth structures, the utricle and saccule. The utricle detects linear horizontal acceleration, while the saccule detects linear vertical acceleration.

  • Note the endolymphatic duct extending from the utricle and saccule out into the posterior cranial fossa, where it terminates in the endolymphatic sac.

• Posteriorly, the semicircular ducts extend from the utricle. Anteriorly, the saccule communicates via the ductus reuniens with the cochlear duct.

• The cochlear duct divides the bony labyrinth of the cochlea into the scala vestibuli and scala tympani, which communicate at the helicotrema of the cochlea. Fluid pressure created by the stapes at the oval window moves through the scala vestibuli and then to the round window via the scala tympani. Movement of perilymph in these channels stimulates the sensory organ of Corti within the cochlear duct, resulting in the generation of a neural impulse related to an auditory stimulus.

A section through the cochlear duct is seen in the lower image.

• First, note the bony labyrinth of the cochlea in brown.

• Within the cochlea, note the cochlear duct suspended in perilymph fluid; the duct occupies the scala vestibuli above and scala tympani below.

• The cochlear duct is bounded superiorly by the vestibular membrane and below by the basilar membrane.

• The sensory organ for hearing, the organ of Corti, is attached to the basilar membrane.

• Note the sensory nerve endings extending from the spiral ganglion of Corti (containing sensory cell bodies of cochlear nerve) to the hair cells.

• Hydraulic pressure changes in the perilymph result in deformation of the cochlear duct and tectorial membrane and stimulation of the hair cells and CN VIII.

The upper image shows the position of cranial nerves (CNs) VII and VIII and the inner ear within the temporal bone.

• Note CNs VII and VIII exiting the cranial cavity via the internal acoustic meatus to enter the petrous portion of the temporal bone.

• CN VII displays a bend, or geniculum, in the temporal bone, before it descends in the facial canal. This geniculum lies between the more anteriorly positioned cochlea and the more posteriorly positioned semicircular canals. Note that the three semicircular canals lie at right angles to one another.

The lower image reveals the anatomical relationships of CN VII, the inner ear, and the dural venous sinuses relative to surface features of the head.

• First, note the position of the auricle of the ear, along with the mastoid process of the temporal bone at the skull base.

• The confluence of the sinuses is seen in midline; recall that it lies over the internal occipital protuberance within the posterior cranial fossa.

• From the confluence, the transverse sinus extends laterally, joining the superior petrosal sinus to form the sigmoid sinus. Recall that the superior petrosal sinus travels along the petrous ridge from the cavernous sinus.

• The sigmoid sinus descends to the jugular foramen at the skull base, where it becomes the internal jugular vein.

The upper image represents a coronal section through the head, demonstrating the layering pattern of meninges and associated vascular elements in the cranial cavity. The lower image is a lateral view of the skull, with the outer table of compact bone removed from the calvaria to reveal diploic and emissary veins.

In the upper image, note the soft tissue surrounding the cranial vault, the scalp.

• • The scalp consists of five layers: epidermis (skin), connective tissue of superficial fascia, aponeurosis (between frontalis and occipitalis muscles of facial expression), loose connective tissue, and pericranium. Note that the first letter of each layer spells “scalp,” as a mnemonic device.

  • The scalp has a significant blood supply, with its arteries and veins traveling in the connective tissue of the second layer, between the epidermis and aponeurosis.

  • Veins of the scalp (e.g., superficial temporal vein in upper image) may unite with emissary veins that course through cranial foramina to open into dural venous sinuses (superior sagittal sinus in upper image) within the cranial vault. Infections may travel along emissary veins from extracranial sites to intracranial compartments.

  • In the lower image, several specific emissary veins are visible, including the parietal, occipital, and mastoid. The parietal emissary veins unite with the superior sagittal sinus, whereas the mastoid emissary veins unite with the sigmoid sinus. The occipital emissary vein joins the transverse sinus.

In the upper image, note that the calvaria consists of an inner and outer table of compact bone, separated by diploe made of cancellous bone with red marrow.

Diploic veins traverse the diploe, draining venous blood from the calvaria to either neighboring extracranial veins or dural venous sinuses. There are four main diploic veins in the skull: frontal, anterior temporal, posterior temporal, and occipital.

• The frontal and anterior temporal diploic veins are located primarily in the frontal bone.

• The posterior temporal diploic vein is housed mainly in the parietal bone.

• The occipital diploic vein is located in the occipital bone.

• The frontal diploic vein typically drains to the supraorbital vein or to the superior sagittal dural venous sinus.

• The anterior temporal diploic vein typically drains to the sphenoparietal sinus or to the deep temporal veins.

• The posterior temporal diploic vein drains to the transverse dural venous sinus.

• The occipital diploic vein drains to the occipital vein, transverse sinus, or confluence of sinuses.

Within the cranial cavity, the brain is invested by three connective tissue coverings known as meninges, visible in the upper image.

• The dura mater is the tough outer layer, the arachnoid mater the thin middle layer, and the pia mater the delicate inner layer directly in contact with the brain itself.

• The dura mater consists of two layers; the outer periosteal dura lines the internal surface of the skull, and the meningeal dura reflects away from the periosteal layer to form dural folds that support the brain and compartmentalize the cranial cavity.

  • Dural venous sinuses are blood-filled gaps between the periosteal and meningeal layers of dura mater.

  • Cerebral veins drain into these sinuses en route to the internal jugular vein.

• The arachnoid forms small tufts, or granulations, that protrude through the meningeal layer of dura into the superior sagittal venous sinus.

• The arachnoid and pia are separated by a fluid-filled space, the subarachnoid space, which contains cerebrospinal fluid.

• Two additional, clinically relevant potential spaces are the epidural space, between the dura and skull, and the subdural space, between the dura and arachnoid.

Superficial cerebral (bridging) veins collect venous blood from the superficial regions of the brain, pierce through the dura mater, and drain into the superior sagittal sinus. Damage to bridging veins may result in a subdural hematoma, or bleed between the meningeal dura and arachnoid.

Deep cerebral veins, by contrast, drain subcortical structures of the cerebrum.

The upper image represents a lateral view of the dura mater in situ, with the superior sagittal sinus and its lateral lacuna opened superiorly. The lower image is a midsagittal section through the skull with the brain and meningeal coverings removed, to demonstrate the arterial supply to the dura mater.

In the upper image, note that the lateral aspect of the skull has been resected to demonstrate the vasculature of the dura mater. Superiorly, the superior sagittal sinus is present between the periosteal and meningeal layers of dura. Within the superior sagittal sinus, note the presence of arachnoid granulations, through which cerebrospinal fluid is filtered into the venous blood of the sinus.

• In addition, several openings of superior cerebral veins are visible draining into the superior sagittal sinus. Extending laterally from the superior sagittal sinus, one of the lateral lacunae is visible, also containing arachnoid granulations for reabsorption of cerebrospinal fluid.

• On the lateral and superficial side of the dura mater, note the arterial supply of the dura mater by branches of the anterior ethmoidal, middle meningeal and occipital arteries.

The lower image reveals the origin of many of the vessels providing arterial blood to the dura mater. The internal and external carotid arteries, along with the vertebral arteries, give rise to several arterial branches that supply the dura.

• The external carotid artery branches to form the maxillary, ascending pharyngeal, and occipital arteries.

  • The maxillary artery provides two branches that supply the dura: the accessory and middle meningeal arteries.

  • The ascending pharyngeal artery provides meningeal branches in the posterior cranial fossa.

  • The occipital artery gives rise to a mastoid branch that supplies the dura mater of the posterior cranial fossa as well.

The internal carotid artery also contributes indirectly to the blood supply to the dura mater.

• • The ophthalmic artery gives rise to the lacrimal artery, which in turn branches to form a recurrent meningeal branch.

  • The meningohypophyseal trunk gives rise to branches supplying the tentorium cerebelli as well as the dura covering the clivus of the skull base.

The vertebral arteries also provide anterior and posterior meningeal branches to the posterior cranial fossa.

The upper image represents a coronal section through the calvaria and cranial vault, demonstrating the layering pattern of meninges and associated vascular elements in the cranial cavity. The lower image is a lateral view of the superficial veins of the brain, with the dura mater reflected superiorly.

In the upper image, note the soft tissue surrounding the cranial vault, the scalp.

• The scalp consists of five layers: the skin (epidermis), connective tissue of the superficial fascia, epicranial aponeurosis (between frontalis and occipitalis muscles of facial expression), loose connective tissue, and pericranium. (As a mnemonic, the first letter of each layer spells “scalp.”)

• The scalp has a significant blood supply, with its arteries and veins traveling in the connective tissue of the second layer, between the epidermis and aponeurosis (in this image, note tributary of superficial temporal vein). Veins of the scalp may unite with emissary veins that course through cranial foramina to open into dural venous sinuses (superior sagittal sinus in this image) within the cranial vault; infections may travel along emissary veins from extracranial sites to intracranial compartments.

Note that the calvaria consists of an inner and outer table of compact bone, separated by diploe made up of cancellous bone with red marrow.

• Diploic veins traverse the diploe, draining venous blood from the calvaria to either neighboring extracranial veins or dural venous sinuses.

Within the cranial cavity, the brain is invested by three connective tissue coverings, the meninges.

• The dura mater is the tough outer layer. The arachnoid mater (in red ) is a thin middle layer, and the pia mater (in green ) is a delicate inner layer directly in contact with the brain itself.

• The dura mater consists of two layers, the outer periosteal dura that lines the internal surface of the skull and the meningeal dura that reflects away from the periosteal layer to form dural folds (e.g., falx cerebri, visible in this image) that support the brain and compartmentalize the cranial cavity. Dural venous sinuses (e.g., superior sagittal sinus in this image) are blood-filled gaps between the periosteal and meningeal layers of dura mater. Cerebral veins drain into these sinuses en route to the internal jugular vein.

• The arachnoid forms small tufts (granulations) that protrude through the meningeal layer of dura into the superior sagittal venous sinus.

• The arachnoid and pia are separated by the subarachnoid space, which contains cerebrospinal fluid.

• In addition, two clinically relevant potential spaces are the epidural space (between dura and skull) and subdural space (between dura and arachnoid).

Superior cerebral (bridging) veins collect venous blood from the superficial regions of the brain, pierce through the dura mater, and drain into the superior sagittal sinus. Damage to bridging veins may result in a subdural hematoma (bleed between meningeal dura and arachnoid).

The lower image demonstrates the external cerebral veins on the superficial surface of the cortex. For orientation, note the position of the superior sagittal sinus, with be bridging veins draining into it.

• The superior anastomotic vein (of Trolard) connects the superior sagittal sinus and the superficial middle cerebral vein (of Sylvius).

• The inferior anastomotic vein (of Labbé) connects the superficial middle cerebral vein and the transverse sinus. Surgically, it must be identified and protected during temporal lobectomy for refractory temporal epilepsy.

• The superficial middle cerebral vein curves anteriorly around the lobe and often drains into the sphenoparietal sinus or cavernous sinus.

Represents a midsagittal section through the cranial cavity, with the brain removed to demonstrate the dural venous sinuses.

For orientation purposes, note the dural fold termed the falx cerebri, responsible for separating and supporting the cerebral hemispheres. Dural venous sinuses associated with the falx cerebri include the superior and inferior sagittal sinuses and the straight sinus.

The superior sagittal sinus is located in the superior attached edge of the falx cerebri. It collects venous blood from bridging cerebral veins, as well as cerebrospinal fluid from arachnoid granulations. It has lateral expansions along its length, termed lateral lacunae, which also contain arachnoid granulations. The superior sagittal sinus terminates posteriorly at the internal occipital protuberance at the confluence of the sinuses.

The inferior sagittal sinus is located in the free inferior border of the falx cerebri. It drains posteriorly into the straight sinus, which is formed by the union of the inferior sagittal sinus and great cerebral vein (of Galen). As with the superior sagittal sinus, the inferior sagittal sinus also terminates in the confluence of the sinuses.

Separating the cerebellar hemispheres, a dural fold termed the falx cerebelli lies in midline of the inferior aspect of the posterior cranial fossa. Traveling in the attached edge of the falx cerebelli, note the occipital sinus draining superiorly to the confluence.

In summary, the confluence of the sinuses receives blood from the superior and inferior sagittal sinuses, as well as from the straight and occipital sinuses.

From the confluence of the sinuses, venous blood drains to the transverse sinuses on each side, which creates a deep groove in the occipital and parietal bones.

The transverse sinuses subsequently drain to the S-shaped sigmoid sinuses on each side, which create deep grooves in the temporal and occipital bones. Each sigmoid sinus is continuous with the internal jugular vein at the level of the jugular foramen.

Two dural venous sinuses are associated with the petrous portion of the temporal bone: the superior and inferior petrosal sinuses.

• The superior petrosal sinus drains posteriorly to join the transverse sinus as it transitions to become the sigmoid sinus.

• The inferior petrosal sinus drains inferiorly to join the sigmoid sinus as it becomes continuous with the internal jugular vein. The basilar venous plexus connects the inferior petrosal sinus with the internal vertebral venous plexus (of Batson).

The cavernous sinuses are located lateral to the sella turcica, housing the pituitary gland. The cavernous sinuses are not visible in this midsagittal section, but the intercavernous sinuses that unite them are visible. In addition, the sphenoparietal sinus that drains along the lesser wing of the sphenoid bone to the cavernous sinus is visible on this plate.

The upper image represents a superior view of the skull base, with cortex, brain stem, and calvaria removed.

• For reference and orientation, note the three depressions, or cranial fossae, on the internal aspect of the skull base.

  • The anterior cranial fossa extends from the frontal bone to the lesser wing of the sphenoid posteriorly.

  • The middle cranial fossa spans from the lesser wing of the sphenoid to the petrous ridge of the temporal bone.

  • The posterior cranial fossa extends from the dorsum sellae posteriorly to include most of the occipital bone.

• In the anterior cranial fossa, note the transverse section through the superior sagittal sinus at the rostral pole of the skull. In the orbit, the superior ophthalmic vein drains posteriorly into the cavernous dural venous sinus in the middle cranial fossa, providing a potential path for the spread of infection from the face or orbit to the cranial vault.

• In the middle cranial fossa, note the sphenoparietal sinuses bilaterally, coursing along the lesser wing of the sphenoid bone. These sinuses drain to the cavernous sinus, also housed in the middle cranial fossa. The cavernous sinuses are located just lateral to the sella turcica, which houses the pituitary gland. In the upper image the left cavernous sinus is exposed, whereas on the right it has been opened to reveal the cavernous segment of the internal carotid artery and the abducens nerve coursing through it.

  • Several cranial nerves have a close anatomical relationship to the lateral dural wall of the cavernous sinus, including the oculomotor and trochlear nerves, as well as the ophthalmic and maxillary divisions of the trigeminal nerve. These cranial nerve relationships with the cavernous sinus are clinically important in cavernous sinus thrombosis, where the nerves may be compressed and their function compromised.

  • Note that the left and right cavernous sinuses are united by anterior and posterior intercavernous sinuses, allowing for the spread of infection between sides. The cavernous sinuses drain to both the basilar venous plexus over the clivus and the superior petrosal sinuses on each side, coursing along the petrous ridge.

• In the posterior cranial fossa, the tentorium cerebelli is intact on the left and has been resected on the right. The superior petrosal sinus lies in the attached edge of the tentorium and drains posteriorly to the transverse sinus.

  • Note the position of the straight sinus, formed by the great cerebral vein (of Galen) and the inferior sagittal sinus, which is not visible in this view. The straight sinus drains into the confluence of the sinuses.

  • From the confluence, the transverse sinuses then transport blood laterally, where they meet the superior petrosal sinus on each side. From here, the transverse sinuses become the sigmoid sinuses, which ultimately exit the jugular foramen to become the internal jugular vein.

  • The glossopharyngeal, vagus, and accessory nerves also exit the jugular foramen and are visible on the right side of the upper image.

The lower image is a coronal section through the cavernous sinus, cortex at the level of the optic chiasm, and skull base.

• • For orientation, first identify the hypophysis (pituitary gland). Note the blue regions just lateral to it on either side, which represent the cavernous sinuses.

  • Traveling through each cavernous sinus, note the cavernous segment of the internal carotid artery and the abducens nerve.

  • In the lateral dural wall of the cavernous sinus, note the oculomotor and trochlear nerves, along with the ophthalmic and maxillary divisions of trigeminal nerve.

  • From this anatomical view of the cavernous sinus, it is easy to understand why cavernous sinus thrombosis first affects the abducens nerve, followed by the nerves traveling through its lateral dural wall. Initial deficits would include an adducted eye on the affected side. Once the lateral wall is compressed, all eye movements on the affected side may be compromised, along with the presence of sensory deficits over the upper face.

The upper image is a lateral view of the cerebrum with the rostral pole to the left. The lower left image colorizes the various lobes of the cerebrum, and the lower right image has the frontal and temporal lobes retracted along the sylvian fissure to demonstrate the insular cortex.

The cerebrum is organized into four lobes: frontal ( red on lower left image), parietal ( blue ), temporal ( orange ), and occipital ( green ).

Each lobe consists of multiple gyri, or folds, separated by sulci, or grooves. The frontal lobe is delineated from the parietal lobe by the central sulcus. The frontal and parietal lobes are separated from the temporal lobe by the lateral sulcus (of Sylvius). The parietooccipital sulcus defines the boundary between the parietal and occipital lobes.

The frontal lobe consists of superior, middle, and inferior frontal gyri. Much of the inferior frontal gyrus forms the operculum, which covers the deeper-lying insular cortex. The inferior frontal gyrus contains Broca’s area, which is involved in language processing. The superior frontal sulcus divides the superior and middle frontal gyri, while the inferior frontal sulcus separates the middle and inferior frontal gyri.

The precentral gyrus lies between the precentral sulcus anteriorly and the central sulcus posteriorly and serves as the primary motor cortex.

The parietal lobe extends from the central sulcus anteriorly to the parietooccipital sulcus posteriorly. It contains the postcentral gyrus (primary somatosensory cortex), along with the superior and inferior parietal lobules. The inferior parietal lobule consists of the supramarginal and angular gyri. The angular gyrus plays a role in language and number processing along with memory and reasoning, whereas the supramarginal gyrus regulates phonological processing and emotional responses.

The occipital lobe extends from the parietooccipital sulcus to the preoccipital notch. On its lateral surface, three occipital gyri may be visible, separated by transverse occipital sulci. The calcarine sulcus is visible as well, around which lies the primary and secondary visual cortices.

The temporal lobe is organized into superior, middle, and inferior temporal gyri. The superior temporal sulcus divides the superior from the middle temporal gyrus, while the inferior temporal sulcus divides the middle from the inferior temporal gyrus.

The lower right image reveals the insula, which is covered in situ by the frontal, parietal, and temporal opercula (“lids”). The circular sulcus surrounds the base of the insula. The insula consists of an anterior lobule that is formed by three short gyri and a posterior lobule that consists of long gyri. The central sulcus of the insula divides the anterior and posterior lobules.

The upper image represents a midsagittal section through the brain and brain stem in situ. The lower image shows a midsagittal section of the cortex with the brain stem resected.

The upper image shows internal features of the cortex, cerebellum, and brain stem.

• The cortex is organized into four lobes: frontal, parietal, temporal, and occipital. The temporal lobe is not visible in this midsagittal view but can be seen in the lower image.

• The medial surface of the frontal lobe is organized by the cingulate sulcus. Superior to the cingulate sulcus, note the continuation of the superior frontal gyrus, which is organized into a medial frontal gyrus and a paracentral lobule. Inferior to the cingulate sulcus is the cingulate gyrus.

• The parietal lobe’s medial surface is characterized by its contribution to the paracentral lobule and the precuneus. The marginal sulcus separates the paracentral lobule from the precuneus.

• The occipital lobe is delineated from the parietal lobe by the parietooccipital sulcus. Just inferior to this sulcus is the cuneus. The calcarine sulcus separates the more superior cuneus from the more inferior lingual gyrus.

• Note that the occipital lobe lies on the dural fold termed the tentorium cerebelli, which contains the straight dural venous sinus. The cerebellum is located inferior to the tentorium cerebelli.

The lower image elucidates the medial aspect of the temporal lobe, including the hippocampus, parahippocampal gyrus, dentate gyrus, and uncus. The parahippocampal gyrus covers the hippocampus and uncus and is bounded inferiorly and laterally by the collateral sulcus. The uncus is the most anterior portion of the parahippocampal gyrus and contains the primary olfactory cortex. The dentate gyrus contributes to the hippocampus.

In the upper image, inferior to the cingulate gyrus, note the corpus callosum, which consists of commissural fibers connecting the cerebral hemispheres.

• The cingulate gyrus and corpus callosum are separated by the sulcus of the corpus callosum.

• The lower image shows the four parts of the corpus callosum, from anterior to posterior, the rostrum, genu, trunk, and splenium.

  • Note that the rostrum lies immediately anterior to the anterior commissure.

  • The lamina terminalis stretches between the anterior commissure and the dorsal surface of the optic chiasm and represents the remnant of the rostral end of the neural tube.

• Attached to the inferior edge of the corpus callosum, identify the septum pellucidum anteriorly and the body of the fornix posteriorly. The fornix consists of three parts, the crus, body, and columns. The body of the fornix allows for communication between the hippocampi, while the columns communicate with the hypothalamus.

• Inferior to the fornix, note the diencephalon, which consists of the thalamus and hypothalamus.

  • The hypothalamic sulcus marks the border between the thalamus and hypothalamus in the midsagittal section.

  • The hypothalamus extends from the lamina terminalis anteriorly to the mammillary body posteriorly.

  • The lamina terminalis forms both the rostral border of the hypothalamus and the rostral wall of the third ventricle.

  • The superior border of the hypothalamus is defined by an imaginary line between the anterior and posterior commissures. The inferior boundary is the infundibulum (stalk) of the pituitary gland, tuber cinereum, and mammillary bodies.

• The brain stem lies inferior to the diencephalon and consists of the midbrain, pons, and medulla. The midbrain is divided into three parts, the tectum (roof), tegmentum (floor), and cerebral peduncles. The cerebral aqueduct separates the tectal plate from the tegmentum.

• The brain has a series of internal cavities known as ventricles filled with cerebrospinal fluid. There are four ventricles, including paired lateral ventricles that are connected to the third ventricle through the interventricular foramen (of Monro). The third ventricle lies in the midline between the two halves of the diencephalon and is connected to the fourth ventricle through the midbrain by the cerebral aqueduct. The fourth ventricle covers the dorsal surface of the brain stem beneath the cerebellum.

Demonstrates the characteristic features of the ventral surface of the cerebrum, with the brain stem sectioned at the level of the midbrain. The cerebellum has been resected.

The left and right cerebral hemispheres are separated by the longitudinal cerebral fissure. Follow this fissure caudally, and note the position of the genu of the corpus callosum and the lamina terminalis.

In considering the ventral anatomy of each lobe, we begin rostrally at the frontal pole. Note the most medial gyrus, termed the straight gyrus, oriented in a rostrocaudal direction. Lateral to the straight gyrus, identify the olfactory sulcus in which the olfactory bulb and tract lie. The region lateral to the olfactory sulcus consists of the orbital gyri. As the olfactory tract courses posteriorly, it divides into the lateral and medial olfactory striae. These striae form the anterior boundary of the anterior perforated substance, pierced by numerous small blood vessels supplying the cortex and deeper regions.

On the ventral surface of the temporal lobe, note the lateral position of the inferior temporal gyrus. Medial to the inferior temporal gyrus is the lateral occipitotemporal gyrus (fusiform gyrus), which extends caudally into the occipital lobe. The most medial gyrus in the temporal lobe is the parahippocampal gyrus, which has a small, medial extension called the uncus. The parahippocampal gyrus forms a major part of the limbic lobe, which encircles the brain stem and plays a role in emotional responses.

The ventral surface of the occipital lobe is characterized by the calcarine sulcus, which begins at the occipital pole and runs forward toward the corpus callosum. The cortex adjacent to the calcarine fissure forms the primary visual area. The wedge-shaped group of small gyri dorsal to the calcarine fissure is the cuneus.

Located centrally in this image, note the section through the midbrain. You can imagine this midbrain section as a “Mickey Mouse” head, with the ears being the cerebral crura (peduncles), the eyes being the red nuclei, and the mouth being the cerebral aqueduct. The chin is formed by two protuberances known as the superior colliculi. The substantia nigra delineates the “ears” from the rest of the “head.”

The rostral border of the midbrain follows the posterior edges of the optic tracts and mammillary bodies. Note the position of the hypophysis (pituitary gland) between the optic chiasm and mammillary bodies. The tuber cinereum of the hypothalamus is continuous with the infundibulum of the pituitary gland. Caudal to the mammillary bodies is a midline furrow termed the interpeduncular fossa that houses the posterior perforated substance, which is an area where arteries penetrate to supply deep structures.

The optic tracts course dorsolaterally to terminate in the lateral geniculate body of the thalamus, just lateral to the midbrain on each side. The lateral geniculate body is associated with visual function. The medial geniculate bodies are associated with auditory function. Just caudal to the medial geniculate bodies, note the splenium of the corpus callosum.

The upper image represents a transparent view of the brain, highlighting the orientation of the ventricular system of the central nervous system. The lower image shows a coronal section through the brain at the level of the mammillary bodies, to highlight the position and anatomy of the choroid plexus, responsible for secreting cerebrospinal fluid (CSF).

The brain is hollow, containing a series of ventricles responsible for CSF production and circulation. The ventricular system consists of paired lateral ventricles (considered the first and second ventricles), a single third ventricle, and fourth ventricle.

Each lateral ventricle consists of three horns named for the cerebral lobes into which they project: frontal, temporal, and occipital horns. CSF, made in the lateral ventricles, travels through the interventricular foramen of Monro to reach the third ventricle.

The third ventricle is sandwiched between the left and right sides of the diencephalon. There is an interthalamic adhesion uniting the two halves of the diencephalon, and the third ventricle is interrupted by this structure.

The third ventricle contains multiple expansions, or recesses, related to key anatomical landmarks. These recesses expand when the third ventricle is enlarged as a result of hydrocephalus.

• The supraoptic recess is located just above the optic chiasm.

• The infundibular recess is positioned just above the pituitary stalk.

• The pineal and suprapineal recesses are located at the posterior margin of the third ventricle, related to the pineal gland.

CSF from the third ventricle travels via the cerebral aqueduct to reach the fourth ventricle. The fourth ventricle lies posterior to the pons and medulla of the brain stem. The fourth ventricle continues as the central canal after it enters the spinal cord. In addition, CSF also exits the fourth ventricle to enter the subarachnoid space via one median aperture of Magendie and two lateral apertures of Luschka.

The lower image represents a coronal section through the brain, demonstrating the lateral and third ventricles.

• For orientation, note the position of the corpus callosum, and just inferior to it, identify the frontal horns of the left and right lateral ventricles.

• The frontal horns of the lateral ventricles are separated by the membranous septum pellucidum, which extends from the corpus callosum to the fornix. Inferior to the fornix, the third ventricle is visible between the left and right sides of the diencephalon (thalamus and hypothalamus).

• The white arrow indicates the continuity of the frontal horn of the lateral ventricle with the third ventricle by way of the interventricular foramen (of Monro).

• Also note the temporal horn of the lateral ventricle on the right side of the image.

CSF is synthesized in the ventricles by the choroid plexus, which is formed by tufts of vascular pia mater ( tela choroidea ), covered by a cuboidal epithelium that is formed by modified ependymal cells (type of glial cell).

• In the lower image, you can track the transformation of standard pia mater in green to choroid plexus in red.

Plate outlines the production and circulation of cerebrospinal fluid (CSF) in a midsagittal section through the central nervous system.

First, note the selected dural venous sinuses shown in this image, including the superior sagittal and straight sinuses. Bridging veins are visible draining the cerebrum into the superior sagittal sinus. Note the projection of arachnoid granulations from the subarachnoid space into the superior sagittal sinus, for reabsorption of CSF from the subarachnoid space into the venous system.

Next, identify the choroid plexus, responsible for synthesizing CSF and visible in the lateral ventricle and third and fourth ventricles.

• Follow the black arrows to track CSF flow from the frontal horn of the lateral ventricle, through the interventricular foramen (of Monro), and into the third ventricle. From the third ventricle, CSF travels through the cerebral aqueduct within the midbrain to reach the fourth ventricle. Inferiorly, CSF flows into the central canal of the spinal cord.

In addition, CSF will exit the fourth ventricle to enter the subarachnoid space via two lateral apertures (foramina of Luschka) and one median aperture (foramen of Magendie).

• White arrows indicate CSF flow in the subarachnoid space.

In some regions surrounding the brain, the subarachnoid space is enlarged to form a cistern. These intracranial cisterns include the cerebellomedullary, quadrigeminal, interpeduncular, chiasmatic, and prepontine cisterns.

The upper image represents a horizontal section through the brain at two levels (A and B) of the basal ganglia. The lower image is a lateral view of subcortical structures associated with the basal ganglia; the rostral end of the complex is to the left.

The basal ganglia are a group of nuclei in the deep white matter that modulate the motor cortex and descending motor pathways.

The chart on the left side of the plate summarizes the components and organization of the basal ganglia. The basal ganglia consist of the caudate nucleus, putamen, and globus pallidus.

• There are various combinations of these nuclei, including the striatum (caudate and putamen), lentiform nucleus (putamen and globus pallidus), and corpus striatum (striatum and lentiform nucleus).

The caudate nucleus is a C-shaped structure closely approximated to the lateral ventricle. The caudate nucleus consists of a head, body, and tail, with the head closely related to the lentiform nucleus and the tail related to the amygdala. The thalamus lies caudal to the caudate nucleus and medial to the lentiform nucleus.

The internal capsule consists of white matter projection fibers and has a close anatomical relationship to the basal ganglia nuclei. It is visible on the upper image.

• The internal capsule consists of an anterior limb, positioned rostrally to separate the caudate from lentiform nucleus.

• The anterior limb is continuous with the genu, or bend, which lies medial to the lentiform nucleus and contains corticonuclear fibers.

• The posterior limb of the internal capsule lies between the thalamus and lentiform nucleus, while the retrolenticular portion of the internal capsule is positioned caudal to the lentiform nucleus and consists of the optic radiations.

• Plate elucidates the anatomy of the thalamus, which plays a critical role in sensory and motor integration. The upper image represents a horizontal section taken at the level of the thalamus. The lower two images are schematic views of the thalamic nuclear organization.

• The upper image demonstrates many of the boundaries of the thalamus.

• Anteriorly, the interventricular foramen (of Monro) defines the rostral border of the thalamus.

• Posteriorly, the pulvinar defines the caudal border of the thalamus. The pulvinar is the largest of the thalamic nuclei and is responsible for integrating visual, auditory, and somatic sensory input.

• Medially, the third ventricle bounds the thalamus, while laterally the posterior limb of the internal capsule limits the thalamus.

The thalamus is organized into anterior, medial, and lateral nuclei, defined by the Y-shaped white matter tract known as the internal medullary lamina.

• The lower left image is a coronal section through the thalamus, with the medial side on the left and the lateral side on the right.

• The lower right image is a superolateral view, showing the left and right thalami, connected by the interthalamic adhesion.

The internal medullary lamina contains nuclei that receive input from a variety of sources, including the reticular formation and other thalamic nuclei; these nuclei project diffusely to various cortical regions.

The anterior tubercle is labeled on the upper image and is also shown in yellow on the lower right image. It is closely associated with the limbic system (specifically, the Papez circuit). It receives input from the hypothalamus and hippocampus and projects to the cingulate gyrus.

The medial nuclei consist of the median, medial, and medial dorsal nuclei. These nuclei play a key role in memory, autonomic regulation, and emotion.

The lateral nucleus is organized into ventral and dorsal tiers.

• The ventral tier includes the ventral anterior, ventral lateral, and ventral posterior nuclei.

  • The ventral anterior nucleus modifies input from the basal nuclei and projects to the premotor cortex.

  • The ventral lateral nucleus regulates somatic motor pathways via the striatum and cerebellum.

  • The ventral posterior nucleus regulates somatic sensory pathways. It consists of three subnuclei: ventral posterolateral nucleus (pain, temperature, and tactile discrimination in trunk and extremities), ventral posteromedial nucleus (pain, temperature, and tactile discrimination in head), and ventral intermedial nucleus (vestibular input).

• The dorsal tier consists of the lateral dorsal and lateral posterior nuclei and the pulvinar.

  • The lateral dorsal nucleus has limbic function, while the lateral posterior communicates with the superior parietal cortex.

  • The pulvinar integrates visual, auditory, and somatic sensory input.

• The lateral geniculate body is a visual relay nucleus, whereas the medial geniculate body is an auditory relay nucleus.

The upper image represents a superior dissection of the hippocampus and fornix, with the rostral pole of the frontal lobe positioned at the top of the image. The lower left image demonstrates the anatomy of the fornix in isolation from surrounding cortical tissue. The lower right image shows a coronal section through the hippocampus.

The hippocampal formation functions in learning and memory. It consists of the dentate gyrus and hippocampus, both of which are visible in the upper image as well as the lower right image. The hippocampal formation projects via the fornix to the septal area and mammillary bodies. It receives afferent input from cerebral association cortex, septal area, and anterior nucleus of the thalamus.

The fornix consists of four parts, the crura, commissure, body, and columns.

• The crura arise from the fimbriae of the hippocampus and arch under the splenium of the corpus callosum, visible on the upper image.

• The commissure connects the crura across midline.

• The body of the fornix is formed by the merging of the crura just inferior to the septum pellucidum.

• Just superior to the interventricular foramen (of Monro), the body of the fornix divides into columns, which curve inferiorly to reach the mammillary bodies.

The upper image represents a posterolateral view of the brain stem, with the cerebrum and cerebellum removed. The lower image demonstrates an anterior view of the brain stem in situ.

The brain stem consists of three parts: medulla, pons, and midbrain.

On the lower image, identify the boundary between the medulla and the spinal cord at the origin of the first cervical (C1) spinal nerve, which is at about the level of the foramen magnum.

• On each side of the midline in the medulla, note a pair of rounded ridges termed the pyramids, formed by the underlying corticospinal tract.

• Immediately lateral to the pyramids there is a pair of oval structures known as the olives.

• The preolivary sulcus lies between the olive and the pyramid on each side and represents the site at which the hypoglossal nerve emerges.

• Dorsolateral to the olive, note the postolivary sulcus, from which the glossopharyngeal (CN IX), vagus (CN X), and spinal accessory (CN XI) nerves emerge.

The dorsal surface of the medulla is best seen on the upper image.

• On either side of the midline, note a pair of rounded ridges, the gracile fasciculus and gracile tubercle, formed by the posterior column and nucleus gracilis, respectively. These represent the afferent fibers for proprioception, vibration, and light touch from the lower extremities.

• Lateral to the gracile fasciculus and tubercle, identify the cuneate fasciculus and tubercle. Deep to these external features are the posterior column and nucleus cuneatus, respectively. These represent the afferent fibers for proprioception, vibration, and light touch from the upper extremities.

On the lower image, note that the pons (“bridge”) is positioned rostral to the medulla. This part of the brain stem forms a bridge-like configuration between the cerebellar hemispheres.

• • The pontomedullary junction is demarcated by a horizontal groove, the bulbopontine sulcus, from which the abducens (CN VI), facial (CN VII), and vestibulocochlear (CN VIII) nerves emerge from medial to lateral, respectively.

  • The lateral edge of this groove (where CNs VII and VIII emerge) is specifically termed the cerebellopontine angle. On the lateral surface of the pons, note the middle cerebellar peduncle, from which the trigeminal nerve (CN V) emerges.

  • On the upper image, note that the dorsal surface of the pons is covered by the fourth ventricle. The cerebellar peduncles form the lateral boundaries of the fourth ventricle, while the superior medullary velum forms the roof.

The midbrain lies between the pons and the diencephalon. The midbrain is bounded caudally by the pons and rostrally by the optic tracts and mammillary bodies.

On the lower image, just caudal to the mammillary bodies, identify the posterior perforated substance in the floor of the interpeduncular fossa. Just lateral to the interpeduncular fossa, note the rounded ridges forming the cerebral crura, or peduncles, carrying the corticospinal or corticonuclear (corticobulbar) fibers from the cortex to the spinal cord or brain stem. The oculomotor nerves emerge from the medial aspect of the cerebral crura in the interpeduncular fossa.

On the upper image, identify the thalami and the optic tracts lying just inferior to them. The optic tract courses dorsolaterally to terminate in the lateral geniculate body of the diencephalon.

• Note two pairs of rounded prominences (quadrigeminal bodies) on the dorsal aspect of the midbrain that form its tectum (roof).

  • The more rostral pair represent the superior colliculi, associated with visual functions. Note the brachium of the superior colliculi, which represents retinal axons bypassing the lateral geniculate body.

  • The more caudal pair represent the inferior colliculi, associated with auditory functions. The brachium of the inferior colliculi is formed by axons that arise in the inferior colliculi and course to the medial geniculate body.

• Note the trochlear nerve exiting from the dorsal aspect of the midbrain near midline just caudal to the inferior colliculi. The trochlear nerves pass ventrolaterally, around the lateral edge of the cerebral peduncles.

The upper image is a posterior view of the brain stem with the cerebral cortex and cerebellum largely resected. The lower image represents a midsagittal section through the diencephalon, brain stem, and cerebellum.

In the upper image, note the spinal cord and three components of the brain stem: medulla, pons, and midbrain.

On the posterior aspect of the spinal cord, note the cuneate and gracile fasciculi, which convey somatosensory information from the upper and lower extremities, respectively.

The medulla is characterized by the cuneate and gracile tubercles from the posterior view. Note the obex, which represents the point where the fourth ventricle narrows to become continuous inferiorly with the central canal of the spinal cord.

The dorsal surface of the pons is covered by the fourth ventricle, which appears as a tent-shaped cavity and is filled with cerebrospinal fluid. The cerebellar peduncles form the lateral boundaries of the fourth ventricle, with the superior medullary velum forming the roof. On either side of the velum lies the superior cerebellar peduncle, which serves as the major pathway carrying information out of the cerebellum.

The floor of the fourth ventricle lies partly in the rostral medulla and partly in the pons. The boundary between the two is marked by the striae medullares, a group of fibers running transversely over the widest part of the floor.

The floor of the fourth ventricle exhibits several distinguishing features. On either side of midline, note a pair of grooves termed the sulcus limitans, which separate laterally located sensory structures from medially positioned motor regions. Medial to the sulcus limitans, identify the facial colliculus, created by the underlying abducens nucleus and fibers of cranial nerve VII that course over it. Caudal and lateral to the facial colliculus is the triangular-shaped vestibular area. Most caudally on the floor of the fourth ventricle, identify two V-shaped areas, the hypoglossal and vagal trigones. The vestibular area, hypoglossal trigone, and vagal trigone are created by the underlying nuclei associated with these nerves.

On the dorsal surface of the midbrain, note the superior and inferior colliculi. The pineal body rests between the superior colliculi in midline. The brachium of the superior colliculus is created by underlying axons from the retina that bypass the lateral geniculate body. The brachium of the inferior colliculus is created by axons that arise in the inferior colliculi and course to the medial geniculate body.

• Collectively, the superior and inferior colliculi are referred to as the quadrigeminal bodies and represent the tectum of the midbrain.

• The trochlear nerve emerges from the dorsal surface near midline just caudal to the inferior colliculi.

The lower image shows a sagittal section through the brain stem.

• First, identify the components of the diencephalon, including the thalamus and hypothalamus, separated by the hypothalamic sulcus.

• The third ventricle lies in midline between the left and right sides of the diencephalon. The third ventricle narrows as it enters the midbrain to form the cerebral aqueduct.

• Posterior to the pons and anterior to the cerebellum, the cerebral aqueduct opens into the wider fourth ventricle. The roof of the fourth ventricle is formed by the superior and the inferior medullary velum. The fourth ventricle is continuous inferiorly with the central canal of the spinal cord.

The upper image represents the dorsal view of the cerebellum. The middle image demonstrates the ventral view, with the cut edges of the cerebellar peduncles visible at the site of attachment to the brain stem. The lower image is a horizontal section at the level of the superior cerebellar peduncle.

The cerebellum is organized into left and right hemispheres with a midline vermis.

The upper image shows that the cerebellum is organized into anterior and posterior lobes, separated by the primary fissure. The anterior lobe regulates muscle tone, and the posterior lobe coordinates voluntary motor activity.

The middle image (ventral view) of the cerebellum shows the anterior and posterior lobes, as well as the flocculonodular lobe ( blue ), which is defined from the posterior lobe via the posterolateral fissure. Note the region of the posterior lobe termed the tonsil, which may herniate inferiorly through foramen magnum in Chiari malformations or with elevated intracranial pressure.

The cerebellar peduncles attach the cerebellum to the brain stem, with the superior peduncle at the level of the midbrain, the middle peduncle at the level of the pons, and the inferior peduncle at the level of the medulla. The superior cerebellar peduncle transmits primarily efferent pathways, while the middle and inferior peduncles are afferent.

The fourth ventricle lies between the cerebellar peduncles and the inferior medullary velum. The superior medullary velum stretches between the superior cerebellar peduncles.

The lower image reveals deep cerebellar nuclei, the more medial fastigial and the most lateral dentate. Between these are the interposed nuclei, the globose and emboliform.

Represents a transparent schematic of the posterior aspect of the brain stem, highlighting the relative positions of the motor (efferent) and sensory (afferent) columns of cranial nerve nuclei. This plate schematically separates the motor components in red from the sensory components in blue.

The organization of nuclear columns in the mature brain stem results from developmental changes that occur in the alar and basal plates of the neural tube. The sulcus limitans separates motor from sensory structures. During development, the left and right sides of the neural tube are flattened laterally, such that the sulcus limitans comes to be positioned in the floor of the fourth ventricle. Nuclei that lie medial to the sulcus limitans are derived from the basal plate and are motor, whereas nuclei that lie lateral to the sulcus limitans are derived from the alar plate and are sensory.

Motor nuclei are organized into three columns.

• Cranial nerves (CNs) III, IV, VI, and XII are considered general somatic efferent (innervate skeletal muscles derived from somites) and are located near the midline.

• Motor nuclei of CNs V, VII, IX, X, and XI are special somatic efferent (innervate skeletal muscles derived from pharyngeal arches) and are located slightly lateral to general somatic efferent neurons.

• Parasympathetic nuclei are from CNs III (Edinger-Westphal nucleus), VII (superior salivatory nucleus), IX (inferior salivatory nucleus), and X (dorsal motor nucleus) and are situated lateral to the special somatic efferent neurons.

Sensory nuclei lie lateral to motor nuclei. General and special visceral afferent neurons are carried by CNs VII, IX, and X, sharing a column that terminates in the solitary tract nuclei. General somatic afferent and special somatic afferent fibers project lateral to the visceral afferent column.

Represents a transparent lateral view of the brain stem with its cranial nerve (CN) nuclei. The anterior surface of the brain stem is directed to the left; the cerebellum is located posteriorly. This diagram demonstrates how different fiber types associated with the various CN nuclei converge to exit the brain stem in their respective cranial nerves.

The oculomotor nerve (CN III) carries somatic motor fibers arising from the oculomotor nucleus, along with preganglionic parasympathetic fibers originating from the accessory oculomotor (Edinger-Westphal) nucleus.

The trochlear nerve (CN IV) carries only somatic motor fibers originating from the trochlear nucleus.

The trigeminal nerve (CN V) carries sensory fibers in all three of its divisions, as well as motor fibers in the mandibular division (V ₃ ).

The abducens nerve (CN VI) carries only somatic motor fibers originating from the abducens nucleus.

The facial motor nucleus sends axons along an unusual course, traveling posteriorly around the abducens nucleus by way of the internal genu of the facial nerve. These motor fibers blend with parasympathetic fibers from the superior salivary nucleus to exit the brain stem in the facial nerve (CN VII). Somatic sensory and taste fibers projecting to the spinal trigeminal and solitary nuclei also travel through the facial nerve.

Vestibular and cochlear nuclei receive fibers traveling through the vestibulocochlear nerve (CN VIII).

The glossopharyngeal nerve (CN IX) carries preganglionic parasympathetic fibers from the inferior salivatory nucleus and motor fibers from the nucleus ambiguus. Sensory fibers in this nerve project to the solitary and spinal trigeminal nuclei.

The vagus nerve (CN X) carries preganglionic parasympathetic fibers from the dorsal motor nucleus and motor fibers from the nucleus ambiguus. Sensory fibers in this nerve project to the solitary and spinal trigeminal nuclei.

The accessory nerve (CN XI) receives motor fibers from the accessory nucleus.

The hypoglossal nerve (CN XII) carries only somatic motor fibers originating from the hypoglossal nucleus.

Summarizes the targets for the motor and sensory fibers of the cranial nerves and demonstrates the exit site for each cranial nerve on a ventral view of the brain.

CN I is the olfactory nerve, which has its sensory cell bodies of origin in the olfactory epithelium in the nasal cavity. It conveys the sense of smell.

CN II is the optic nerve, which has its sensory cell bodies of origin in the ganglion cells of the retina. It conveys the sense of sight.

CN III is the oculomotor nerve, which carries both somatic motor and parasympathetic fibers. Parasympathetics innervate the ciliary and sphincter pupillae muscles, while the somatic motor fibers supply all extraocular muscles except lateral rectus and superior oblique.

CN IV is the trochlear nerve, which carries somatic motor fibers to the superior oblique muscle.

CN V is the trigeminal nerve, which carries sensory fibers from the head and motor fibers to muscles derived from the first pharyngeal arch, including muscles of mastication, the tiny tensors (tensor tympani and tensor veli palatini), mylohyoid, and anterior belly of digastric.

CN VI is the abducens nerve, which carries somatic motor fibers to the lateral rectus muscle.

CN VII is the facial nerve, which is divided into a motor component that supplies the muscles of facial expression, posterior belly of digastric, and stylohyoid and an intermediate nerve. The intermediate nerve carries parasympathetic fibers to the submandibular, sublingual, lacrimal, and nasal glands, along with taste from the anterior two thirds of the tongue.

CN VIII is the vestibulocochlear nerve, which carries sensory signals related to hearing and balance from the inner ear.

CN IX is the glossopharyngeal nerve, which carries parasympathetic innervation to the parotid gland and motor fibers to the stylopharyngeus muscle, along with taste from the posterior one third of the tongue and sensation from the middle ear, pharynx, and tonsillar fossa.

CN X is the vagus nerve, which carries parasympathetic innervation to the thorax and proximal gastrointestinal (GI) tract; motor innervation to muscles of the pharynx, larynx, and palate; and sensory innervation from the thorax, GI tract, larynx, pharynx, and external ear.

CN XI is the accessory nerve, which carries motor innervation to the sternocleidomastoid and trapezius muscles.

CN XII is the hypoglossal nerve, which carries motor innervation to the intrinsic and most extrinsic muscles of the tongue (except palatoglossus, supplied by CN X).

Outlines the course of cranial nerve I, the olfactory nerve. The cell bodies of origin for the olfactory nerve belong to bipolar neurons housed in the olfactory epithelium in the roof of the nasal cavity. These neurons send their central projections through the cribriform plate of the ethmoid bone to synapse on mitral cells and tufted cells in the olfactory bulb.

Axons from the mitral and tufted cells largely project by way of the lateral olfactory tract to the primary olfactory cortex in the piriform lobe. Some fibers take the medial olfactory tract to reach basal limbic forebrain structures such as the septal area.

Outlines the course of cranial nerve II, the optic nerve. The cell bodies of origin belong to the retinal ganglion cells. These ganglion cell axons exit the eye to form the optic nerve and enter the skull by way of the optic canal in the sphenoid bone.

In the cranial cavity, the optic nerves merge at the optic chiasm and then divide again distally to form the optic tracts that project to the lateral geniculate bodies. While each optic nerve carries visual information from the ipsilateral retina, note that the optic tracts carry information from both eyes to the thalamus because fibers from the nasal retina cross in the chiasm.

From the lateral geniculate bodies, the geniculocalcarine tract, or optic radiations, extend to the primary visual cortex flanking the calcarine sulcus. The cuneus lies superior to the calcarine sulcus and receives input from the superior retina (inferior visual field), while the lingual gyrus lies inferior to the calcarine sulcus and receives input from inferior retina (superior visual field).

Outlines the course and targets of the oculomotor, trochlear, and abducens nerves.

Cranial nerve III, the oculomotor nerve, is a mixed motor nerve containing somatic motor and parasympathetic fibers. The somatic motor fibers have their cell bodies of origin in the oculomotor nucleus, while the preganglionic parasympathetic fibers have their cell bodies in the accessory oculomotor nucleus. These merge as the oculomotor nerve exits the brain stem, travels in the lateral wall of the cavernous sinus, and enters the orbit via the superior orbital fissure. Once in the orbit, the oculomotor nerve divides into superior and inferior divisions.

• The parasympathetic fibers follow the inferior division to reach the ciliary ganglion, where they synapse. The postganglionic fibers then “hitch a ride” on short ciliary nerves to reach the ciliary and sphincter pupillae muscles.

• The somatic motor fibers to the superior rectus and levator palpebrae superioris muscles take the superior division, while those innervating the medial and inferior rectus and inferior oblique muscles take the inferior division.

CM IV, the trochlear nerve, has its cell bodies of origin in the trochlear nucleus. It uniquely exits the brain stem on its posterior surface. After coursing ventrolaterally around the cerebral peduncles, the trochlear nerve passes through the lateral wall of the cavernous sinus and enters the orbit via the superior orbital fissure to innervate the s uperior o blique muscle. As a mnemonic, the “chemical formula” of the extraocular muscles in this case is “SO ₄ ” (sulfate).

CN VI, the abducens nerve, has its cell bodies in the abducens nucleus. It travels within the cavernous sinus and enters the orbit via the superior orbital fissure to innervate the l ateral r ectus (reflected in this plate). The “formula” for this is “LR ₆ ”.

To complete the mnemonic, that leaves a ll the r est of the extraocular muscles to be innervated by CN III (“AR ₃ ”).

Outlines the course and targets of cranial nerve V, the trigeminal nerve. It consists of three divisions, the ophthalmic (V ₁ ), maxillary (V ₂ ), and mandibular (V ₃ ). Each of these divisions carries somatic sensory fibers, whereas motor fibers travel only in the mandibular division.

Three sensory nuclei and one motor nucleus are associated with the trigeminal nerve: mesencephalic, principal, and spinal nucleus as the sensory nuclei and trigeminal motor nucleus.

The cell bodies of origin for the sensory neurons of the trigeminal nerve are housed in the trigeminal ganglion in the middle cranial fossa. From the ganglion, the three divisions emerge and exit the cranial cavity via distinct foramina. The ophthalmic nerve enters the orbit via the superior orbital fissure, the maxillary nerve enters the pterygopalatine fossa via the foramen rotundum, and the mandibular nerve enters the infratemporal fossa via the foramen ovale.

The ophthalmic division (CN V ₁ ) divides into three branches in the orbit, the frontal, lacrimal, and nasociliary nerves. The frontal nerve gives rise to the supraorbital and supratrochlear nerves. The nasociliary nerve gives rise to the posterior and anterior ethmoidal nerves, the long and short ciliary nerves, and the infratrochlear nerve.

The maxillary division (CN V ₂ ) gives rise to the zygomatic nerve, which divides into the zygomaticofacial and zygomaticotemporal nerves. The maxillary division sends sensory branches through the pterygopalatine ganglion, which emerge as the greater and lesser palatine nerves, the pharyngeal nerve, and the posterior lateral nasal and nasopalatine nerves. The maxillary nerve continues distally as the infraorbital nerve.

The mandibular division (CN V ₃ ) gives rise to sensory branches, including the buccal, auriculotemporal, lingual, inferior alveolar, and mental nerves. The motor branches supply muscles of mastication, mylohyoid muscle, and the tiny tensors (tensor veli palatini, tensor tympani).

Outlines the course and targets of cranial nerve VII, the facial nerve. The facial nerve is associated with several brain stem nuclei, including the facial motor nucleus, superior salivary nucleus, and solitary nucleus.

The facial nerve arises from the brain stem as two roots, the motor root and the intermediate nerve, which contains taste and parasympathetic fibers. These roots merge at the internal acoustic meatus, where they enter the temporal bone.

Within the temporal bone, the facial nerve divides into two parts at the level of its sensory ganglion, the geniculate ganglion. The main trunk of the facial nerve proceeds inferiorly through the facial canal, while the parasympathetic greater petrosal nerve branches anteriorly from the geniculate ganglion.

Within the facial canal, the facial nerve gives rise to several branches, including the motor branch to stapedius and chorda tympani. The chorda tympani carries taste fibers from the anterior tongue and parasympathetic fibers; it passes through the middle ear cavity and emerges from the temporal bone at the petrotympanic fissure to enter the infratemporal fossa. Chorda tympani “hitches a ride” on the lingual nerve of the trigeminal nerve; its taste fibers follow the lingual nerve to the tongue, whereas its parasympathetic fibers exit the lingual nerve to synapse in the submandibular ganglion in the floor of the mouth. Postganglionic parasympathetic fibers then innervate the neighboring submandibular or sublingual salivary glands.

The remainder of the facial nerve continues through the facial canal to exit the base of the skull at the stylomastoid foramen, where it enters the parotid gland and branches to supply the muscles of facial expression, stylohyoid, and posterior belly of digastric.

The greater petrosal nerve, another parasympathetic branch of the facial nerve, originates at the level of the geniculate ganglion within the temporal bone. It courses anteriorly to reenter the middle cranial fossa and passes over the foramen lacerum to approach the posterior opening of the pterygoid canal. Here, it unites with the deep petrosal nerve to form the nerve of the pterygoid canal. This nerve courses anteriorly to reach the pterygopalatine fossa, where the parasympathetic fibers synapse in the pterygopalatine ganglion. Postganglionic fibers then hitch a ride on branches of the maxillary nerve to reach their targets, including the lacrimal gland and the nasal and palatal glands.

Represents a horizontal section through the middle cranial fossa and temporal bone, at the level of the internal acoustic meatus. The anatomy of both the facial and the vestibulocochlear nerve is demonstrated in this view.

The highlight of this plate is the course and targets of cranial nerve VIII, the vestibulocochlear nerve, which conveys the special senses of hearing and balance from the inner ear.

Hearing is initiated when vibration translocates the microvilli of hair cells against the tectorial membrane in the organ of Corti. These hair cells are innervated by sensory neurons whose cell bodies are located in the spiral, or cochlear, ganglion in the temporal bone. These sensory neurons project centrally to the anterior and posterior cochlear nuclei in the brain stem.

Balance and equilibrium are regulated by movement of the hair cells of the crista ampullaris of the semicircular ducts and the maculae of the utricle and saccule. These hair cells are innervated by sensory neurons with their cell bodies in the vestibular ganglion in the temporal bone. These sensory neurons project centrally to the vestibular nuclei in the brain stem, as well as to the flocculonodular lobe of the cerebellum.

In addition, plate demonstrates the proximal anatomy of the facial nerve (CN VII). Note its entrance into the internal acoustic meatus. At the genu of the facial nerve, it turns into the facial canal. The geniculate sensory ganglion of the facial nerve is located at the genu. At the level of the geniculate ganglion, the parasympathetic greater petrosal nerve branches anteriorly from the facial nerve.

Outlines the course and targets of cranial nerve IX, the glossopharyngeal nerve. Several brain stem nuclei are associated with this nerve, including the spinal nucleus of the trigeminal nerve, solitary tract nucleus, nucleus ambiguus, and inferior salivatory nucleus.

The sensory modalities of the glossopharyngeal nerve include sensation from the external ear, posterior tongue, oropharynx, tympanic cavity, carotid sinus, and carotid body. Motor components include innervation to the stylopharyngeus muscle and parotid gland.

The glossopharyngeal nerve emerges from the medulla and exits the cranial cavity via the jugular foramen. At the level of the jugular foramen, two sensory ganglia are present, the superior and inferior ganglia of CN IX. These ganglia contain the sensory cell bodies for the nerve.

The glossopharyngeal nerve gives rise to the tympanic nerve, just inferior to the jugular foramen. The tympanic nerve carries sensory and preganglionic parasympathetic fibers through the middle ear. The sensory fibers remain in the tympanic cavity, while the parasympathetic fibers emerge as the lesser petrosal nerve. The lesser petrosal nerve reenters the middle cranial fossa briefly and then exits via the foramen ovale. On entry into the infratemporal fossa, the lesser petrosal nerve synapses in the otic ganglion, located on the deep surface of the mandibular nerve. Postganglionic parasympathetic fibers from the otic ganglion then “hitch a ride” on the auriculotemporal nerve of the mandibular nerve to reach the parotid gland.

The glossopharyngeal nerve proceeds distal to the tympanic branch to give rise to a motor branch to the stylopharyngeus muscle, along with sensory branches to the mucosa of the oropharynx, tonsillar fossa, and posterior tongue (for both taste and somatic sensation).

In addition, the glossopharyngeal nerve supplies sensory innervation to the carotid sinus and carotid body, which serve as baroreceptors and chemoreceptors, respectively.

Outlines the course and targets of cranial nerve X, the vagus nerve. Several brain stem nuclei are associated with this nerve, including the spinal nucleus of the trigeminal, nucleus of the solitary tract, nucleus ambiguus, and dorsal nucleus of the vagus.

The sensory modalities of the vagus nerve include sensation from the external ear, laryngopharynx and larynx, epiglottis, and thoracic and abdominal organs. Motor components include innervation of skeletal muscles of the palate, pharynx, and larynx, as well as parasympathetic fibers to thoracic and abdominal organs.

The vagus nerve emerges from the medulla of the brain stem and exits the cranial cavity via the jugular foramen. At the level of the jugular foramen, the superior ganglion of CN X contains the sensory cell bodies of somatic sensory neurons associated with the vagus nerve. Just inferior to the jugular foramen, the inferior, or nodose, ganglion contains visceral sensory cell bodies for the vagus nerve.

The vagus nerve enters the carotid sheath just inferior to the level of the inferior ganglion.

A motor pharyngeal branch provides motor innervation to the pharyngeal constrictor muscles via the pharyngeal plexus.

Just distal to the pharyngeal nerve, the vagus nerve gives rise to the superior laryngeal nerve, which divides into an internal laryngeal nerve that provides sensory innervation to the upper laryngeal mucosa and the external laryngeal nerve, which provides motor innervation to the cricothyroid muscle of the larynx.

The vagus then gives rise to cervical cardiac branches to the cardiopulmonary plexus.

The vagus branches asymmetrically to form the left and right recurrent laryngeal nerves, which provide motor and sensory innervation to the larynx. The motor fibers innervate all intrinsic laryngeal muscles except the cricothyroid, while the sensory fibers innervate the lower laryngeal mucosa. On the right, the recurrent laryngeal nerve loops around the subclavian artery, whereas on the left it loops lower, around the aortic arch.

The left and right vagus nerves give rise to thoracic cardiac and pulmonary branches, before uniting to form the esophageal plexus over the anterior surface of the esophagus.

From the esophageal plexus, anterior and posterior vagal trunks emerge and enter the abdomen via the esophageal hiatus in the diaphragm.

Anterior view of the spinal cord, lower brain stem, skull base, and sternocleidomastoid and trapezius muscles. It demonstrates the course of cranial nerve XI, the accessory nerve.

The accessory nerve originates from the nucleus of the accessory nerve in the upper five to six cervical spinal cord segments. The rootlets of the accessory nerve emerge between the anterior and posterior roots of cervical spinal nerves. The accessory nerve ascends into the foramen magnum and quickly turns to exit the skull base via the jugular foramen.

CN XI then descends to reach the deep surface of the sternocleidomastoid muscle, innervating it. The accessory nerve crosses the posterior triangle of the neck to innervate the deep surface of the trapezius muscle.

Demonstrates the origin and course of cranial nerve XII, the hypoglossal nerve. The lower motor neurons associated with this nerve have their cell bodies of origin in the hypoglossal nucleus in the medulla. Their axons exit the cranial cavity via the hypoglossal canal.

Shortly after exiting the cranial cavity, the hypoglossal nerve picks up C1 and C2 cervical nerve fibers that transiently “hitch a ride” to form the ansa cervicalis, which supplies motor innervation to most of the infrahyoid or strap muscles.

C1 fibers also travel directly along the hypoglossal nerve to innervate the thyrohyoid muscle.

Distal to the ansa cervicalis, the hypoglossal nerve enters the floor of the oral cavity to supply all the intrinsic and most of the extrinsic tongue muscles (except palatoglossus, supplied by the vagus nerve, since it is actually a muscle of the palate rather than the tongue).

The anterior rami of cervical spinal nerves C1 to C4 form the cervical plexus, which has both sensory and motor components.

The superficial sensory branches of the cervical plexus emerge at the midpoint of the posterior border of the sternocleidomastoid muscle. They include the lesser occipital nerve (C2), which supplies the neck and scalp posterior to the external ear, and the great auricular nerve (C2‒3), which supplies skin over the mastoid process, the ear, and angle of the mandible. The transverse cervical nerve (C2‒3) supplies the skin of the anterior neck, while the supraclavicular nerves (C3‒4) supply the skin over the shoulder.

The deeper motor branches of the cervical plexus form the ansa cervicalis, or nerve loop of the neck. The ansa consists of a superior root, formed by C1 fibers, and an inferior root, formed by C2 and C3 fibers. The superior and inferior roots join inferiorly to form a loop, from which distinct motor branches emerge to innervate sternohyoid, sternothyroid, and omohyoid muscles. The thyrohyoid is innervated directly by C1 fibers that “hitch a ride” on the hypoglossal nerve.

The phrenic nerve originates from C3‒5 and provides motor and sensory innervation to the diaphragm.

Also visible in this plate, the accessory nerve picks up branches from the cervical plexus, providing its muscular targets (sternocleidomastoid and trapezius) with pain and proprioceptive fibers.

Represents a lateral view of deep structures in the neck, with a particular focus on autonomic nerves.

The cervical portion of the sympathetic trunk is fully visible in this view, coursing from the skull base to the level of the first rib. The cervical sympathetic trunk consists of three main ganglia: superior, middle, and inferior cervical ganglia. The inferior cervical ganglion often fuses with the first thoracic sympathetic ganglion to form the cervicothoracic, or stellate, ganglion. A vertebral ganglion may also be present at the level of the vertebral artery, giving rise to a nerve loop termed the ansa subclavia, which communicates with the stellate ganglion.

The superior cervical ganglion lies at the C1‒2 vertebral level and provides postganglionic sympathetic fibers to the internal and external carotid arteries. It also gives rise to superior cervical cardiac, or cardiopulmonary splanchnic, nerves.

The middle cervical ganglion is located at the level of the cricoid cartilage at vertebral level C6. It sends postganglionic fibers to C5 and C6 spinal nerves via gray rami, as well as middle cervical cardiac nerves to the cardiopulmonary plexus. The middle cervical ganglion also contributes fibers that “hitch a ride” on branches of the external carotid artery to reach the thyroid gland.

Represents a sagittal section through the head and neck, highlighting sympathetic and parasympathetic nerves.

Begin by identifying the sympathetic trunk, with the superior cervical ganglion situated at the skull base. Note its contributions to the external carotid arterial plexus.

The parasympathetic cranial nerves for the head include the oculomotor, facial, and glossopharyngeal nerves.

The oculomotor nerve carries parasympathetic fibers through its inferior division. These parasympathetics synapse in the ciliary ganglion, before being distributed to targets in the eye via short ciliary nerves.

The facial nerve has two distinct parasympathetic pathways, the greater petrosal nerve and chorda tympani.

The greater petrosal nerve of the facial nerve branches at the level of the geniculate ganglion. It merges with the sympathetic deep petrosal nerve to form the nerve of the pterygoid canal. The parasympathetic fibers in the nerve of the pterygoid canal synapse in the pterygopalatine ganglion, and postganglionic fibers are then distributed to nasal and palatal mucosa.

The chorda tympani branches from the facial nerve in the facial canal and exits the temporal bone at the petrotympanic fissure to enter the infratemporal fossa, where it “hitches a ride” on the lingual nerve of the mandibular division of the trigeminal nerve. The parasympathetic fibers exit the lingual nerve at the level of the submandibular ganglion to synapse and then innervate either the submandibular or sublingual glands.

The glossopharyngeal nerve gives rise to a tympanic nerve that carries preganglionic parasympathetic fibers destined to synapse in the otic ganglion. Postganglionic fibers are then distributed to the parotid gland via the auriculotemporal nerve of the mandibular nerve.

Outlines the parasympathetic and sympathetic pathways to smooth muscular structures in the eye.

The parasympathetic path begins in the accessory oculomotor (Edinger-Westphal) nucleus, which houses the preganglionic parasympathetic cell bodies. These neurons send their axons out through CN III and travel through its inferior division to reach the ciliary ganglion, where they synapse. Postganglionic parasympathetic fibers then travel via the short ciliary nerves to reach the ciliary and sphincter pupillae muscles.

The sympathetic path begins in the intermediolateral nucleus in the spinal cord. These neurons send their axons into the sympathetic trunk, where they ascend to synapse in the superior cervical ganglion. From here, postganglionic sympathetic fibers travel on the internal carotid artery as a periarterial plexus. They travel on the nasociliary root of the ciliary ganglion to reach the long and short ciliary nerves, which they use to reach their target, the dilator pupillae muscle.

Highlights the two distinct parasympathetic pathways associated with the facial nerve. Both pathways begin in the same brain stem nucleus, the superior salivatory nucleus. These preganglionic parasympathetic fibers exit the facial nerve and enter the greater petrosal nerve or the chorda tympani.

The greater petrosal nerve ultimately synapses in the pterygopalatine ganglion and distributes its postganglionic fibers to the lacrimal gland, nasal and palatal mucosal glands, and pharynx.

The chorda tympani parasympathetic fibers “hitch a ride” on the lingual nerve of the trigeminal to reach the submandibular ganglion, where they synapse. Postganglionic parasympathetic fibers then distribute to innervate the submandibular or sublingual glands.

Sympathetic fibers to these targets originate in the intermediolateral gray horn in the spinal cord and enter the sympathetic trunk via white rami communicantes. They ascend through the sympathetic trunk to reach the superior cervical ganglion, where they synapse. From here, the postganglionic fibers use branches of the internal and external carotid arteries to reach their targets. For the targets of the pterygopalatine ganglion, sympathetics do exit the internal carotid artery to travel in the deep petrosal nerve. Sympathetics therefore traverse the pterygopalatine ganglion without synapsing to reach their targets in the lacrimal, nasal, palatal, and pharyngeal glands.

Highlights the parasympathetic path to the parotid gland.

Preganglionic parasympathetic cell bodies for this path are housed in the inferior salivatory nucleus. They send their axons out through the glossopharyngeal nerve (CN IX), following the tympanic branch just inferior to the jugular foramen at the level of the inferior ganglion of CN IX. These preganglionic parasympathetic fibers travel through the middle ear as part of the tympanic plexus of nerves overlying the promontory of the middle ear. They then emerge from the tympanic plexus as the lesser petrosal nerve, which ultimately synapses in the otic ganglion in the infratemporal fossa. Postganglionic parasympathetic fibers then “hitch a ride” on the auriculotemporal nerve of the mandibular division of the trigeminal nerve to reach the parotid gland.

By contrast, preganglionic sympathetic fibers destined for the parotid gland begin in the intermediolateral nucleus of the spinal cord. Their axons exit the spinal cord via the ventral root of the spinal nerve and enter the sympathetic trunk via the white rami communicantes. Here, the axons ascend to the superior cervical ganglion, where they synapse and subsequently travel along the external carotid artery and its branches to reach the parotid gland.

Summarizes taste pathways conveyed by the facial, glossopharyngeal, and vagus nerves.

Taste from the anterior two thirds of the tongue is conveyed by the chorda tympani branch of the facial nerve (CN VII). These fibers travel along the lingual nerve, then along chorda tympani as it travels in isolation through the petrotympanic fissure. The chorda tympani originates from CN VII as it traverses the facial canal. The cell bodies for these taste neurons are housed in the sensory ganglion of CN VII, the geniculate ganglion. From the geniculate ganglion, central processes of the first-order taste fibers then travel through the intermediate nerve to reach the brain stem, where they project to the rostral part of the nucleus of the solitary tract.

Taste from the posterior one third of the tongue is conveyed by the glossopharyngeal nerve (CN IX). The cell bodies of these first-order neurons are housed in the inferior, or petrosal, ganglion of CN IX. They send their central processes via CN IX into the brain stem to terminate in the nucleus of the solitary tract.

Taste from the epiglottis is conveyed by the vagus nerve (CN X). The cell bodies of these first-order taste neurons are housed in the inferior, or nodose, ganglion of CN X and send their central processes via CN X into the brain stem to terminate in the nucleus of the solitary tract.

Second-order neuronal cell bodies for the taste pathway are housed in the nucleus of the solitary tract. They project to the pontine taste area as well as to the ventral posteromedial (VPM) nucleus of the thalamus by way of the central tegmental tract.

From the VPM nucleus, third-order neurons project to the gustatory region of the sensory cortex.

Plate provides a lateral view of two key arteries supplying the brain, the internal carotid and vertebral (basilar).

The internal carotid artery arises from the common carotid artery at the level of the hyoid bone. The common carotid artery is a branch of the brachiocephalic trunk on the right side of the body and of the aortic arch on the left. The internal carotid artery enters the skull base via the carotid canal in the temporal bone. It courses within the cavernous sinus as the carotid siphon.

• Ultimately, the internal carotid gives rise to two terminal branches, the anterior and middle cerebral arteries.

The vertebral artery arises from the subclavian artery on each side of the body. It enters the transverse foramen of the C6 vertebra on each side and ascends until it emerges from the transverse foramen of C1 to course in a groove along the posterior arch of C1. From here, each vertebral artery then ascends through foramen magnum to access the cranial cavity.

• At the lower border of the pons, the left and right vertebral arteries join to form the basilar artery.

Plate provides a unique posterior view of the course of the internal carotid artery. Clinicians often classify several segments of the internal carotid artery based on their anatomical positions and relationships with neighboring structures.

The cervical part of the internal carotid artery extends from the carotid bifurcation up to its entry into the skull base at the carotid canal. This portion of the internal carotid lacks branches.

Once the internal carotid artery enters the carotid canal, it is then classified as the petrous, or horizontal, part of the vessel. This segment has two branches, the caroticotympanic artery and artery of the pterygoid canal.

• The maxillary artery also gives rise to a distinct artery of the pterygoid canal.

The internal carotid artery emerges from the petrous temporal bone via the superior opening of the carotid canal and subsequently enters the cavernous sinus. This represents the cavernous part of the internal carotid artery. It gives rise to the meningohypophyseal trunk and inferolateral trunk.

The intracranial part of the internal carotid artery gives rise to the ophthalmic and superior hypophyseal arteries. It ultimately branches into the anterior and middle cerebral arteries.

Plate summarizes the arterial supply to the brain, including the internal carotid and vertebrobasilar circulations, and how they relate to one another through anastomoses.

The internal carotid arteries arise from the common carotid arteries. The right common carotid artery arises from the brachiocephalic trunk of the aorta, while the left arises directly from the aortic arch.

• The internal carotid arteries then ascend through the neck without branching.

• They enter the skull base, travel through the temporal bone and cavernous sinus, and enter the cranial cavity, where they terminally branch into an anterior and a middle cerebral artery on each side.

• The anterior cerebral arteries anastomose by way of the anterior communicating artery.

The vertebral arteries branch from the subclavian artery on each side and ascend through the neck in the transverse foramina of the cervical vertebrae.

• They enter the foramen magnum and merge to form the basilar artery on the pons.

• The anterior spinal artery is formed by contributions from each distal vertebral artery.

• The basilar artery gives rise to the anterior inferior cerebellar artery, along with the superior cerebellar artery.

• Ultimately, the basilar artery terminally branches to form the right and left posterior cerebral arteries.

• The posterior cerebral arteries anastomose with the internal carotid arteries by way of a posterior communicating artery on each side. This completes the circle of Willis, formed by the anterior communicating, anterior cerebral, internal carotid, posterior communicating, and posterior cerebral arteries.

The upper image provides an in situ view of the arteries of the brain from an inferior perspective. The lower image represents a horizontal section through the brain at the level of the midbrain, with the temporal lobe resected.

In the upper image, first identify the cut edges of the internal carotid arteries, located just caudal to the optic nerves.

• Each internal carotid artery branches into an anterior and a middle cerebral artery.

• The anterior cerebral arteries course rostrally toward the frontal lobes and are connected by the anterior communicating artery.

• The middle cerebral arteries dive deep to the temporal lobe in this view on the left; on the right side the temporal lobe has been resected to better demonstrate the lateral course of the middle cerebral artery and its lenticulostriate branches.

The vertebral arteries ascend along the medulla, giving rise to the posterior inferior cerebellar arteries (PICAs), which give rise to the posterior spinal arteries and supply the dorsolateral medulla and inferior cerebellum.

• The vertebral arteries then give rise to medial branches that form the anterior spinal artery.

• The vertebral arteries merge as the basilar artery at the inferior border of the pons.

• The basilar artery quickly gives rise to the anterior inferior cerebellar artery (AICA), which supplies the inferior surface of the cerebellum.

• Just rostral to the exit of the abducens nerve from the brain stem, note the labyrinthine artery, which perfuses the cochlea and vestibular apparatus.

• As the basilar artery continues rostrally over the pons, several pontine arteries are visible, responsible for supplying the corticospinal tracts.

• Just caudal to the exit point for the oculomotor nerve, note the superior cerebellar artery on each side.

• Just rostral to the oculomotor nerve, the basilar artery terminates as the left and right posterior cerebral arteries, which provide the major blood supply for the occipital lobe and brain stem.

• The posterior cerebral arteries anastomose with the internal carotid arteries through the posterior communicating arteries.

The lower image shows a more detailed view of the branching pattern of the anterior, middle, and posterior cerebral arteries.

• The anterior cerebral artery is one of two terminal branches of the internal carotid artery. It supplies the optic chiasm and the medial surfaces of the frontal and parietal lobes. The anterior cerebral artery gives rise to the medial striate artery of Heubner, which supplies the caudate and putamen, as well as the anterior limb of the internal capsule.

• The middle cerebral artery is the other of the two terminal branches of the internal carotid artery. It supplies the motor and sensory cortices, along with Broca’s and Wernicke’s speech areas.

• The posterior cerebral artery is formed by the bifurcation of the basilar artery. It provides the primary blood supply to the midbrain. The posterior cerebral artery gives rise to posterior choroidal arteries that supply the posterior thalamus, pineal body, and choroid plexus of the lateral ventricle.

The upper image highlights the vessels associated with the cerebral arterial circle of Willis in isolation. The lower image includes a similar view in situ.

The cerebral arterial circle is formed by the anterior communicating, anterior cerebral, internal carotid, posterior communicating, and posterior cerebral arteries. This anastomotic circle gives rise to penetrating arteries that supply the ventral diencephalon and midbrain.

The lower image demonstrates the relationship of the circle of Willis to the optic chiasm and hypophysis (pituitary gland). Note the superior hypophyseal artery branching from the internal carotid artery to supply the optic nerve and chiasm, along with the adenohypophysis and infundibulum. The inferior hypophyseal artery arises from the meningohypophyseal trunk of the cavernous part of the internal carotid artery and supplies the neurohypophysis.

The upper image represents an anterior view of the brain with the frontal and parietal lobes retracted to demonstrate the corpus callosum and its blood supply.

First, note the cut edge of the internal carotid artery. It terminally branches to form the anterior and middle cerebral arteries.

The anterior cerebral artery travels rostrally in the longitudinal fissure, supplying blood to the medial aspect of the cerebral hemispheres. It gives rise to frontal, callosomarginal, and pericallosal arteries.

At the level of the optic chiasm, note the anterior communicating artery uniting the two anterior cerebral arteries. This artery is prone to aneurysms, which may result in visual deficits.

The middle cerebral artery supplies the lateral aspect of the cerebral hemisphere via several branches, including the orbitofrontal, precentral, and central sulcal arteries. In addition, the anterior and posterior parietal, angular, and temporal arteries branch from the middle cerebral artery.

The lower image represents a coronal section to demonstrate the middle and anterior cerebral circulations. Note the lenticulostriate arteries, which serve as the first branches of the middle cerebral artery and supply the caudate, putamen, and anterior limb of internal capsule. The course of the precentral and central sulcal arteries and the temporal branches is also elucidated in this view.

The upper image represents a lateral view of the cerebral hemisphere with its blood supply intact. Note that the temporal lobe is retracted to better demonstrate the course of the middle cerebral artery. The lower image is a midsagittal section through the cerebrum, showing its vascularization by the anterior and posterior cerebral arteries.

In the upper image, the main branches of the middle cerebral artery are highlighted, supplying most of the lateral surface of each cerebral hemisphere.

• Note the anterior, middle, and posterior temporal arteries supplying different regions of the temporal lobe. The posterior temporal artery also supplies part of the occipital lobe.

• The angular artery supplies the angular gyrus.

• The anterior and posterior parietal arteries supply the parietal lobe.

• The precentral and central arteries supply the frontal lobe, along with the orbitofrontal artery.

The lower image highlights the anterior cerebral artery, which provides the main blood supply to the medial surface of the frontal and parietal lobes, and the posterior cerebral artery, which vascularizes the occipital lobe.

• The key branches of the anterior cerebral artery include the orbital, frontopolar, callosomarginal, and pericallosal arteries.

• The posterior cerebral artery gives rise to anterior and posterior temporal and parietooccipital arteries.

• Note the calcarine artery, which supplies the primary visual cortex.

Represents a lateral view of the brain, highlighting the blood supply in the posterior cranial fossa. The cranial nerves are numbered for reference.

Identify the vertebral artery, and note that its first branch is the posterior spinal artery.

Next, the posterior inferior cerebellar artery (PICA) arises and supplies the lateral medulla. Occlusion of PICA results in Wallenberg syndrome, which involves dysphonia, dysarthria, and dysphagia.

The two vertebral arteries then merge to form the basilar artery.

• The first branch from the basilar artery is the anterior inferior cerebellar artery (AICA), which supplies the cerebellum and pons.

• The labyrinthine artery arises next from the basilar artery and supplies the inner ear.

Pontine arteries supply a variety of structures, including the corticospinal and corticobulbar tracts, along with the medial lemniscus.

The superior cerebellar artery supplies the rostral pons, caudal midbrain, and superior cerebellum.

The posterior cerebral artery supplies most of the midbrain and thalamus.

Highlights the deep cerebral veins of the posterior cranial fossa.

The great cerebral vein (of Galen) is a very short vein formed by two internal cerebral veins at the level of the splenium of the corpus callosum.

The internal cerebral veins drain the thalamus, striatum, caudate, and internal capsule. The great cerebral vein joins the inferior sagittal sinus to form the straight sinus. The straight sinus then empties into the confluence of sinuses.

The basal vein (of Rosenthal) drains venous blood from the frontal cortex, anterior corpus callosum, and cingulate gyrus, as well as the insula and opercular cortex. The basal vein empties into the great cerebral vein.

The cerebellum and medulla drain their venous blood ultimately into the great cerebral vein and several of the dural venous sinuses.

The upper image represents a superior view of a horizontal section at the level of the straight sinus. The lower image shows an inferior view of the deep veins of the brain.

In the upper image, note the position of the corpus callosum for orientation. The lateral ventricles lie just inferior to the corpus callosum and are bounded laterally by the caudate nuclei. The septum pellucidum is evident with the columns of the fornix in its caudal edge. Note the thalamus positioned caudal to the fornix.

The deep cerebral veins include the internal cerebral veins and the great cerebral vein (of Galen). The internal cerebral veins lie superior to the thalami, drain posteriorly into the great cerebral vein, and receive blood from the anterior vein of the septum pellucidum and the thalamostriate vein. The septal and thalamostriate veins meet at the venous angle, a landmark located at the interventricular foramen (of Monro).

In the lower image, note the great cerebral vein (of Galen) receiving blood from the basal vein (of Rosenthal) on either side of the midbrain.

Subependymal veins are positioned deep to the ependymal lining of the ventricles. The primary subependymal veins include the paired internal cerebral, thalamostriate, and septal veins.

The internal cerebral veins lie adjacent to one another in the roof of the third ventricle for most of their course. They fuse to form the great cerebral vein (of Galen) posteriorly.

Each internal cerebral vein receives blood from the thalamostriate, or terminal, vein at the venous angle. Here, the anterior septal vein joins the internal cerebral vein.

The dorsal vein of the corpus callosum extends around the splenium of the corpus callosum and empties into the great cerebral vein just caudal to its junction with the internal cerebral veins.

The upper image provides an overview of the anatomical relationships of the hypothalamic nuclei. The lower image shows the anatomical connections between the hypothalamus and hypophysis (pituitary gland).

In the upper image, note that the hypothalamus extends from the optic chiasm to the mammillary bodies. It is organized into three regions, derived from their blood supply, from rostral to caudal: the anterior region; the tuberal, or middle, region; and the mammillary, or posterior, region.

• The key nuclei in the anterior region are the supraoptic and paraventricular. These nuclei project axons to the posterior pituitary, where they release antidiuretic hormone (ADH, vasopressin) into capillary beds.

• The key nuclei in the middle region are the arcuate, ventromedial, and dorsomedial. The arcuate nucleus plays a key role in the production of releasing and inhibiting hormones that are transported via the hypophyseal portal system to regulate the adenohypophysis.

• The key nuclei in the posterior region are the mammillary bodies and posterior nucleus.

In the lower image, note that the hypothalamus is closely related to the hypophysis, connected to it by the infundibulum.

The hypophysis consists of two lobes: the posterior pituitary (neurohypophysis), made of neural tissue, and the anterior pituitary (adenohypophysis), made of glandular tissue.

The posterior pituitary lobe is an extension of hypothalamic neurons. The axons of these neurons descend as the hypothalamohypophyseal tract within the infundibulum and end in the posterior pituitary. The posterior pituitary lobe stores and secretes hormones produced by the hypothalamus into the blood.

By contrast, the anterior pituitary lobe does not contain nerve fibers from the hypothalamus. Communication between the hypothalamus and anterior pituitary is through a system of blood vessels, the hypothalamohypophyseal portal system. Hypothalamic neurons synthesize releasing and inhibiting hormones that regulate the activity of hormone-producing cells in the anterior pituitary.

The hypothalamus‒pituitary complex is the command center of the endocrine system.

The upper image in this plate shows the position of the hypothalamus at the base of the brain, just posterior to the optic chiasm. The hypothalamus is connected anatomically and functionally to the pituitary by way of a stem termed the infundibulum. The pituitary gland itself consists of an anterior lobe and a posterior lobe.

The lower image in the plate focuses on the vascularity of the hypothalamus and lobes of the pituitary. The posterior pituitary is often considered an extension of the neurons from specific nuclei in the hypothalamus (namely, the paraventricular and supraoptic nuclei).

The anterior and posterior pituitary lobes share the same venous drainage via the anterior and posterior hypophyseal veins. They have distinctive arterial supplies.

Hypothalamic hormones act on the anterior pituitary via blood vessels known as the hypophyseal portal system. The anterior pituitary is supplied by a branch of the internal carotid artery, the superior hypophyseal artery. The artery first forms a capillary network around the hypothalamus. Blood is then transported from this network by way of portal veins to a second capillary network around the anterior pituitary.

The hypothalamic releasing and inhibiting hormones pass through the primary capillary network to portal veins, which carry them to the anterior pituitary. Hormones from the anterior pituitary produced in response to the releasing hormones enter a secondary capillary plexus before draining into the systemic circulation (hypophyseal veins).

The upper image is a magnetic resonance angiogram showing the connectivity of the cerebral arteries.

• The internal carotid artery gives rise to two terminal branches seen here, the anterior and middle cerebral arteries. The anterior cerebral arteries are united by the anterior communicating artery.

• The vertebral arteries unite to form the basilar artery, which ultimately terminates as two posterior cerebral arteries. The posterior cerebral arteries are united with the internal carotid arteries by the posterior communicating artery.

The lower image is a magnetic resonance venogram that demonstrates the superficial and deep venous systems of the brain.

• Superficial cerebral veins (bridging veins) drain into the superior sagittal sinus. The superior sagittal sinus drains to the confluence of sinuses posteriorly.

• The internal cerebral veins drain to the great cerebral vein (of Galen), which joins the inferior sagittal sinus to form the straight sinus. The straight sinus drains to the confluence of sinuses.

• From the confluence, blood drains to the transverse sinus, then to the sigmoid sinus, and ultimately to the internal jugular vein.

The upper magnetic resonance (MR) image is a sagittal section through the head.

• Note the corpus callosum with its more rostral genu and caudal splenium. The lateral ventricle is located just below the corpus callosum.

• Note the regions of the brain stem, including the midbrain, pons, and medulla. The tectum (“roof”) of the midbrain is labeled.

• The 4th ventricle is visible posterior to the pons and anterior to the cerebellum.

The middle MR image is a horizontal slice at the level of the pons and cerebellum. The frontal pole is located at the top of the image, and the cerebellum is visible at the bottom. The spaces containing cerebrospinal fluid appear white on this image, including the 4th ventricle.

• Note the nose and eyes anteriorly, with the ethmoidal sinus forming the medial wall of the orbit.

• Posterior to the ethmoid sinus, note the sphenoidal sinus. Lateral to the sphenoid sinus, note the temporal lobe of the cortex and the trigeminal cave, formed by dura mater.

• Note the position of the internal carotid artery, as well as the basilar artery on the pons.

The lower MR image is a horizontal section at the level of the head of the caudate nucleus. First, identify the gray versus the white matter.

• Note the longitudinal cerebral fissure separating the right and left hemispheres.

• Note the genu and splenium of the corpus callosum, with the lateral ventricles accompanying them. The head of the caudate nucleus lies just caudal to the frontal horn of the lateral ventricle on each side.

• Identify the anterior limb of the internal capsule, and follow it caudally to form the genu and then the posterior limb. The 3rd ventricle lies between the thalami.

The surface anatomy of the back can be divided into regions, as demonstrated by the inset on the lower left side of the plate. Note the midline vertebral region, which terminates inferiorly as the sacral region. The vertebral region is flanked laterally by the scapular and infrascapular regions. Inferior to the infrascapular regions lie the lumbar regions.

The main image of this plate demonstrates how the surface anatomy of the back is characterized by bony and muscular landmarks that are associated with the vertebral column and upper limbs.

• The vertebral region marks the position of the vertebral spinous processes along the midline of the back. The vertebral region is continuous with the intergluteal (natal) cleft inferiorly.

• The most prominent bump near the base of the neck, in the midline of the back, is the spinous process of vertebra C7.

• The erector spinae muscle forms lateral elevations on either side of the posterior median furrow, particularly in the lumbar region.

• An imaginary horizontal line from the apex of each iliac crest of the hip bones locates the position of vertebra L4, a key landmark for lumbar puncture with no risk of damage to the spinal cord.

• The gluteal region is located inferior to the iliac crests, extending laterally to the greater trochanter of the femur on each side. The gluteus maximus muscle is the most superficial of the muscles in the hip. The upper third of the gluteus medius muscle is visible superior to the gluteus maximus muscle.

• Superiorly, the external occipital protuberance of the skull is visible and provides a key attachment site for the trapezius muscle. The proximal attachments of the trapezius span from the skull to attach to the nuchal ligament in the neck, as well as to the spinous processes of vertebrae C7‒T12. Distally, the trapezius attaches along the lateral aspect of the clavicle, as well as to the acromion and spine of the scapula, as is visible in this plate.

• At the lower border of the trapezius, the latissimus dorsi muscle is visible, forming the broadest muscle of the back. The latissimus dorsi attaches along the spinous processes of the lower six thoracic vertebrae and iliac crest.

This plate reveals three anatomical views of the isolated vertebral column: anterior, lateral, and posterior. The vertebral column consists of 33 vertebrae, with 7 cervical, 12 thoracic, 5 lumbar, 5 fused sacral, and 4 fused coccygeal vertebrae.

In the left lateral view, note the presence of four curvatures: cervical, thoracic, lumbar, and sacral.

• The cervical and lumbar lordoses are concave posteriorly.

• The thoracic and sacral kyphoses are concave anteriorly.

• The thoracic and sacral curvatures are termed primary curvatures because they are present at birth.

• The cervical and lumbar curvatures are secondary curvatures because they become prominent as an infant begins to hold the head upright, stand, and walk.

This plate demonstrates key features of thoracic vertebrae from superior, lateral, and posterior views. Thoracic vertebrae are located in the upper region of the back and exhibit specialized costal facets enabling them to articulate with the ribs.

A typical vertebra consists of a body, an arch, and several processes.

The vertebral body is located anteriorly and represents the weight-bearing component of the vertebra.

The vertebral arch is located posterior to the vertebral body and consists of paired pedicles and laminae.

• The pedicles are foot-like processes that attach to the vertebral body.

• The laminae are thin plates of bone that close the vertebral foramen posteriorly.

The vertebral foramina of successive vertebrae form the vertebral canal, which houses the spinal cord and its meninges, along with spinal nerve roots.

The processes of each vertebra consist of spinous processes that project posteriorly or posteroinferiorly in the median plane formed by the union of left and right laminae, left and right transverse processes that extend posterolaterally from the point of union of pedicles and laminae, and left and right superior and inferior articular processes (zygapophyses) that arise between each pedicle and lamina, forming facet (zygapophyseal) joints between adjacent vertebrae. In thoracic vertebrae, these facets are nearly vertical.

On the upper left image, a standard thoracic vertebra (T6) exhibits a vertebral body with bilateral costal facets (demifacets) to house the heads of the ribs. From T2 to T9, these facets occur in pairs on adjacent vertebrae to articulate with the head of the rib numbered as the inferior vertebra (head of rib 5 articulates with superior costal facet of vertebra T5). Note that on T12 vertebra, there is only a single costal facet on each side that articulates with the head of the rib.

The transverse process provides a site for vertebral articulation with the costal tubercle by way of the transverse costal facet.

The spinous process provides an attachment site for vertebral ligaments as well as intrinsic and extrinsic back musculature. Thoracic spinous processes are long and slender, angling inferiorly.

On the lateral view of T6, note the presence of vertebral notches located superior and inferior to each pedicle. Adjacent vertebral notches come together to form intervertebral foramina, through which the true spinal nerve exits the vertebral canal.

This plate demonstrates key features of lumbar vertebrae from superior, lateral, and posterior views. Lumbar vertebrae are located in the lower region of the back and exhibit specialized features that enable them to support the weight of the body. This plate also reveals the internal anatomy of the intervertebral disc that lies between adjacent vertebral bodies (except C1 and C2).

The intervertebral disc provides sturdy attachments between vertebral bodies, along with serving as an important shock absorber. Each disc consists of an outer annulus fibrosus and an inner nucleus pulposus.

• The annulus fibrosus is formed by rings of fibrocartilage.

• The nucleus pulposus forms the hydrated core of the disc.

• The intervertebral discs are the largest avascular structures in the body.

A herniated intervertebral disc occurs when the annulus fibrosus is compromised by trauma or degenerative disease such that the nucleus pulposus prolapses, often compressing spinal nerves.

Lumbar vertebrae consist of large vertebral bodies and sturdy vertebral arches. Each vertebral arch is formed by two pedicles and two laminae, enclosing the vertebral foramen. Collectively, the vertebral foramina form the vertebral canal, which houses the spinal cord and spinal nerve roots. Extending laterally from the vertebral arch are long transverse processes and short, broad, horizontally oriented spinous processes. On the posterior aspect of the lumbar transverse processes, an accessory process is visible, which serves as an attachment for intertransversarii muscles.

Lumbar vertebrae articulate with one another by way of superior and inferior articular processes. Each lumbar superior articular process exhibits a mammillary process that serves as an attachment site for deep back musculature (multifidus and intertransversarii).

This plate demonstrates the radiologic anatomy of the vertebral column.

When examining an anteroposterior (AP) radiograph of the spine (upper image), the “owl” analogy is often used; the pedicles appear at the eyes of the owl, while the spinous process represents the beak. If one pedicle is absent, this condition is termed “winking owl” sign, where the winking eye is the missing pedicle.

When evaluating the thoracic spine, it is important to evaluate alignment, following the corners of the vertebral bodies from one level to the next. The vertebral bodies, pedicles, spinous and transverse processes, and ribs should be visible. The size of the vertebral bodies and intervertebral disc spaces should gradually increase in size from superior to inferior.

In the lower (magnetic resonance) image, note the vertebral bodies anteriorly, with intervening intervertebral discs.

• The vertebral canal containing the spinal cord is located just posterior to the vertebral bodies; note the termination of the spinal cord at its conus medullaris at approximately L2 vertebral level.

• Inferior to conus medullaris, note the lumbar cistern, which is an enlargement of the subarachnoid space extending to vertebral level S2. This space contains cauda equina, filum terminale, and cerebrospinal fluid and serves as the site for lumbar puncture and spinal anesthesia.

This plate demonstrates the anatomy of the sacrum and coccyx from anterior and posterior views, as well as in midsagittal and transverse planes.

The sacrum is a wedge-shaped bone formed by the fusion of five sacral vertebrae. The sacrum articulates superiorly with the fifth lumbar (L5) vertebral body and laterally at its articular surface for the ilium on either side. Inferiorly, the sacrum articulates with the coccyx, formed by the fusion of four coccygeal vertebrae. The anterior edge of the first sacral (S1) vertebra forms the sacral promontory, which serves as an important bony landmark for obstetrical measurements.

The sacrum is highly specialized and lacks the standard appearance of the more superior vertebral column.

• Anteriorly, the vertebral bodies are fused to form a smooth pelvic surface.

• Posteriorly, the rudimentary spinous processes form the median sacral crest.

• The intermediate sacral crest is the remnant of the articular processes.

• The lateral sacral crest represents the transverse processes.

The vertebral canal is continuous with the sacral canal of the sacrum and it gives rise to an internal intervertebral foramen through which the true spinal nerve emerges. The anterior and posterior rami of the sacral spinal nerves, however, exit via distinct openings known as the anterior and posterior sacral foramina.

Inferiorly, the sacrum lacks laminae and spinous processes at L5, which results in the sacral hiatus, an opening leading into the sacral canal. This hiatus can be located by identifying the sacral cornua, or horns, which form the inferior articular processes of S5. Caudal epidural injections are administered at the sacral hiatus.

This plate demonstrates vertebral ligaments of the lumbar and sacrococcygeal regions of the spine from lateral and posterior views. The image on the right has the posterior aspect of the vertebral arch removed superiorly, to expose the posterior aspect of the vertebral bodies and the vertebral canal.

On the left lateral view, note that the anterior side of the vertebral column is directed to the left, while the posterior side is to the right. The vertebral bodies and their associated intervertebral discs are supported anteriorly by the anterior longitudinal ligament. This ligament is wide and present at the entire length of the spine from the occiput to the sacrum; it prevents hyperextension of the vertebral column. Posteriorly, adjacent spinous processes are supported by interspinous ligaments and the overlying cord-like supraspinous ligaments that connect the tips of the spines.

On the posterior view, note the narrow posterior longitudinal ligament traveling vertically from the posterior aspect of the body of C2, inferiorly to the sacrum along the vertebral bodies and their associated intervertebral discs. This narrow ligament allows for most intervertebral disc herniations to occur posteriorly because of a lack of support in this region.

More inferiorly in the posterior view, note the ligamentum flavum (in yellow ), spanning between adjacent laminae. Posterior sacroiliac ligaments unite the intermediate crest of the sacrum with the ilium of the hip bone, helping to support the sacroiliac joint on each side. Iliolumbar ligaments attach the transverse processes of L5 to the iliac bone on each side, supporting the lumbosacral joint.

The sacrococcygeal ligaments reinforce the sacrococcygeal joint.

The sacrotuberous ligament passes from the ilium, sacrum, and coccyx to the ischial tuberosity. The sacrospinous ligament courses from the sacrum and coccyx to the ischial spine. These two ligaments are critical in preventing superior and posterior rotation of the sacrum.

This plate demonstrates vertebral ligaments in the lumbar region from a left lateral view and anterior view of the vertebral arch.

In the upper image, the anterior surface of the vertebral column is oriented to the left (characterized by the presence of vertebral bodies), while the posterior surface is to the right (characterized by the presence of spinous processes). Note that the vertebral bodies and their intervening intervertebral discs are supported by the broad anterior longitudinal ligament and the narrower posterior longitudinal ligament. Posterior to the vertebral bodies, the vertebral canal is visible, with its exit points for the spinal nerves visible as intervertebral foramina.

Recall that the vertebral arch extends posteriorly to enclose the vertebral canal at each level, and that the arch consists of paired pedicles and laminae. The ligamentum flavum spans adjacent laminae, supporting them and preventing hyperflexion of the vertebral column. Interspinous ligaments connect adjacent spinous processes, while the cord-like supraspinous ligaments unite the tips of the spinous processes.

The lower left image elucidates the anatomy of the intervertebral disc. Note the ring-like lamellae of the annulus fibrosus that insert into the cartilage end plates of the vertebral bodies. The collagen fibers forming each layer travel obliquely from one vertebra to the next and are oriented in opposite direction to the adjacent lamellae. The anterior longitudinal ligament overlies the collagen lamellae of the intervertebral disc.

The lower right image is oriented as if the observer is standing in the vertebral canal looking posteriorly toward the vertebral arch. Note the cut ends of the pedicles and the laminae extending medially to complete the arch posteriorly. The ligamentum flavum is clearly visible supporting adjacent laminae.

This plate provides a posterior view of the spinal cord and ventral rami of spinal nerves, with the vertebral arches removed by laminectomy. Note the cut edges of the pedicles bilaterally.

The spinal cord begins at the level of the foramen magnum of the occipital bone, where it is continuous with the medulla of the brain stem. The spinal cord extends inferiorly to the L1 or L2 vertebral level, where it terminates as the conus medullaris. Thus the spinal cord is shorter than the vertebral column.

An extension of pia mater known as the filum terminale extends from the tip of conus medullaris to the coccyx to stabilize the spinal cord inferiorly. The spinal cord is invested by meninges, with the outer layer the dura mater. The dura mater forms a dural sac that terminates inferiorly at S2 vertebral level.

Because the spinal cord is shorter than the vertebral column, lumbar and sacral nerve roots are the longest, forming the cauda equina in the inferior aspect of the vertebral canal. These roots must travel long distances before reaching the appropriate site of exit (intervertebral foramen or sacral foramen).

Anterior rami of spinal nerves can either remain segmental, as seen in the thoracic region, where they form intercostal nerves. Alternatively, multiple anterior rami can unite to form a somatic nerve plexus, such as the brachial, lumbar, and sacral plexus.

This plate demonstrates the naming convention of spinal nerves to vertebrae. The image on the left is a sagittal section through the vertebral column, with its anterior side facing to the right and its posterior side facing to the left. Note the numbered vertebral bodies, spanning from C1 to the coccyx.

The spinal cord is shown in the vertebral canal and is colorized by regional spinal cord segments ( green, cervical; blue, thoracic; purple, lumbar; red, sacral and coccygeal). Cervical spinal nerves exit superior to the vertebrae for which they are numbered; for example, C1 spinal nerve emerges above C1 vertebra. Because there are eight cervical spinal nerves and only seven cervical vertebrae, C8 spinal nerve exits inferior to C7 vertebra and superior to T1 vertebra. This results in a change in the numbering scheme for the spinal nerves inferior to this point, with each being numbered for the vertebra superior to their exit; for example, T1 spinal nerve exits inferior to T1 vertebra.

The image on the left also demonstrates that the spinal cord is shorter than the vertebral canal; note that the conus medullaris terminates at L1‒2 vertebral level. As a result, the spinal nerve roots for lumbar, sacral, and coccygeal nerves are much longer than those for cervical or thoracic nerves. The collection of long nerve roots in this area forms the cauda equina, so named because it resembles a horse’s tail.

The images on the right side elucidate the anatomical basis for intervertebral disc herniations and the resulting nerve impingement. Because the nerves exit the intervertebral foramen relatively superiorly, typically a herniation at L4‒5 affects the L5 rather than the L4 spinal nerve. If the herniation occurs medially, it may affect more inferior nerves as well (L4‒5 herniation affects L5 spinal nerve and potentially S1‒-4 spinal nerves as well).

This plate shows the dermatome map of the anterior and posterior aspects of the trunk and limbs.

A dermatome is a strip of skin innervated by one spinal nerve. Clinical studies of lesions of spinal nerve branches have provided the information used for dermatome maps of the innervation of the skin by specific spinal nerves. These maps are used clinically to help localize neurologic deficits, as are found in a radiculopathy. The viruses that infect spinal nerves, such as the herpes zoster virus, often have a clinical presentation of a painful dermatome.

The dermatomes of the trunk are organized in a regular and predictable manner, with T4 residing at the level of the nipples, T10 at the level of the umbilicus, and L1 in the inguinal region.

Developmentally, the limb buds grow out of the trunk, with the thumb and great toe directed superiorly. The upper limb buds arise from levels C5‒T1, and their innervation reflects this pattern, with the C6 dermatome located over the thumb, the C7 dermatome over digits I and III, and the C8 dermatome over digits IV and V. The lower limb buds arise from levels L2‒S2, and their innervation reflects this pattern, with L1‒4 innervating the medial surfaces of the lower limbs, L4 supplying the great toe, and S1 supplying the fifth toe.

This plate demonstrates the spinal cord and its meningeal coverings, along with the anatomy of the spinal nerve and its branches.

In the upper image, note that the spinal cord is invested by three connective tissue coverings: the outer dura mater, intermediate arachnoid mater, and inner pia mater.

The dura mater, or “tough mother,” forms a longitudinal sheath around the spinal cord that terminates at S2 vertebral level inferiorly. The dura extends over the nerve roots in dural root sheaths as the nerve roots emerge from the spinal cord to form the true spinal nerve. These sheaths blend with the epineurium, or connective tissue covering of the spinal nerve distally.

Deep to the dura mater is the arachnoid mater, so named for its spiderweb-like appearance. The arachnoid encloses the subarachnoid space, which houses cerebrospinal fluid.

Deep to the arachnoid is the pia mater, or “delicate mother.” This layer closely follows all of the sulci and fissures of the spinal cord. The pia mater also forms lateral, tooth-like extensions termed denticulate ligaments, which support the spinal cord laterally as they insert into the overlying dura mater. At the caudal end of the spinal cord, the pia mater reflects off the spinal cord to form the filum terminale, which courses inferiorly to attach at the coccyx and stabilize the spinal cord longitudinally.

Between the dura and the bone is a potential space, the epidural space, which normally contains a small amount of fat and vertebral veins. Another potential space, the subdural space, is between the arachnoid and dura mater and can fill with blood or pus under pathologic conditions. Also, the subarachnoid space is between the arachnoid and pia mater and is normally filled with cerebrospinal fluid.

In the lower image, the dura and arachnoid mater have been removed to reveal the anatomy of the spinal nerves emerging from the spinal cord. Note that the gray matter of the spinal cord has been isolated superiorly, to demonstrate its H-shaped configuration into three horns, dorsal, lateral, and ventral. White matter surrounds the gray matter in the spinal cord parenchyma.

The ventral horn of the spinal cord houses neuronal cell bodies responsible for providing somatic motor innervation to skeletal muscles of the body. These neurons extend their axons out the rootlets of the ventral root and into the ventral root of the spinal nerve.

The dorsal horn of the spinal cord receives sensory input from the body via rootlets of the dorsal root of the spinal nerve. The cell bodies of the first-order sensory neurons are housed in the dorsal root, or spinal ganglion, located on the dorsal root.

The dorsal and ventral roots of the spinal nerve join briefly before the spinal nerve divides into a dorsal and ventral ramus, or branch.

• The dorsal rami of spinal nerves supply the back with sensory and motor innervation.

• The ventral rami supply the limbs and anterolateral body wall with sensory and motor innervation.

Note the rami communicantes, which allow for sympathetic fibers to enter and exit the sympathetic trunk from the ventral ramus.

White rami carry preganglionic sympathetic fibers.

Gray rami carry postganglionic sympathetic fibers.