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Cardiovascular System
General organization
The cardiovascular system consists of the heart, which pumps blood throughout the body, and the blood vessels, which are a closed network of tubes that transport the blood. There are three types of blood vessels:
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Arteries—which transport blood away from the heart;
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Veins—which transport blood toward the heart;
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Capillaries—which connect the arteries and veins, are the smallest of the blood vessels, and are where oxygen, nutrients, and wastes are exchanged within the tissues.
This eBook will only focus on the arterial components of the cardiovascular system.
Heart, pulmonary trunk, ascending aorta, and aortic arch
Heart
The heart functionally consists of two pumps separated by a partition ( Fig. 1.1 ). The right pump receives deoxygenated blood from the body and sends it to the lungs. The left pump receives oxygenated blood from the lungs and sends it to the body. Each pump consists of an atrium and a ventricle separated by a valve. The thin-walled atria receive blood coming into the heart, whereas the relatively thick-walled ventricles pump blood out of the heart. Exiting the heart are the pulmonary trunk from the right ventricle and the ascending aorta from the left ventricle.
Pulmonary trunk
The pulmonary trunk is contained within the pericardial sac ( Fig. 1.2 ), is covered by the visceral layer of serous pericardium, and is associated with the ascending aorta in a common sheath. It arises from the conus arteriosus of the right ventricle at the opening of the pulmonary trunk slightly anterior to the aortic orifice and ascends, moving posteriorly and to the left, lying initially anterior and then to the left of the ascending aorta. At approximately the level of the intervertebral disc between vertebrae TV and TVI, anterior-inferior and to the left of the bifurcation of the trachea, opposite the left border of the sternum and posterior to the third left costal cartilage, the pulmonary trunk divides into the right and left pulmonary arteries.
Right pulmonary artery
The right pulmonary artery is longer than the left and passes horizontally across the mediastinum ( Fig. 1.3 ). It passes:
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anteriorly and slightly inferiorly to the tracheal bifurcation and anteriorly to the right main bronchus, and
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posteriorly to the ascending aorta, superior vena cava, and upper right pulmonary vein.
The right pulmonary artery enters the root of the lung and gives off a large branch to the superior lobe of the lung. The main vessel continues through the hilum of the lung, gives off a second (recurrent) branch to the superior lobe, and then divides to supply the middle and inferior lobes.
Left pulmonary artery
The left pulmonary artery is shorter than the right and lies anterior to the descending aorta and posterior to the superior pulmonary vein ( Fig. 1.3 ). It passes through the root and hilum and branches within the lung.
Ascending aorta
The ascending aorta is contained within the pericardial sac and is covered by a visceral layer of serous pericardium, which also surrounds the pulmonary trunk in a common sheath ( Fig. 1.2A ).
The origin of the ascending aorta is the aortic orifice at the base of the left ventricle, which is level with the lower edge of the third left costal cartilage, posterior to the left half of the sternum. Moving superiorly, slightly forward and to the right, the ascending aorta continues to the level of the second right costal cartilage. At this point, it enters the superior mediastinum and is then referred to as the arch of the aorta.
Immediately superior to the point where the ascending aorta arises from the left ventricle are three small outward bulges opposite the semilunar cusps of the aortic valve. These are the posterior, right, and left aortic sinuses. The right and left coronary arteries originate from the right and left aortic sinuses, respectively.
Right coronary artery
The right coronary artery originates from the right aortic sinus of the ascending aorta. It passes anteriorly and then descends vertically in the coronary sulcus, between the right atrium and right ventricle ( Fig. 1.4A ). On reaching the inferior margin of the heart, it turns posteriorly and continues in the sulcus onto the diaphragmatic surface and base of the heart. During this course, several branches arise from the main stem of the vessel:
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An early atrial branch passes in the groove between the right auricle and ascending aorta and gives off the sinu-atrial nodal branch ( Fig. 1.4A ), which passes posteriorly around the superior vena cava to supply the sinu-atrial node.
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A right marginal branch is given off as the right coronary artery approaches the inferior (acute) margin of the heart ( Fig. 1.4A,B ) and continues along this border toward the apex of the heart.
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As the right coronary artery continues on the base/ diaphragmatic surface of the heart, it supplies a small branch to the atrioventricular node before giving off its final major branch, the posterior interventricular branch ( Fig. 1.4A ), which lies in the posterior interventricular sulcus.
The right coronary artery supplies the right atrium and right ventricle, the sinu-atrial and atrioventricular nodes, the interatrial septum, a portion of the left atrium, the posteroinferior one-third of the interventricular septum, and a portion of the posterior part of the left ventricle.
Left coronary artery
The left coronary artery originates from the left aortic sinus of the ascending aorta. It passes between the pulmonary trunk and the left auricle before entering the coronary sulcus. Emerging from behind the pulmonary trunk, the artery divides into its two terminal branches, the anterior interventricular and the circumflex ( Fig. 1.4A ).
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The anterior interventricular branch (left anterior descending artery — LAD) ( Fig. 1.4A,C ) continues around the left side of the pulmonary trunk and descends obliquely toward the apex of the heart in the anterior interventricular sulcus ( Fig. 1.4 A,C ). During its course, one or two large diagonal branches may arise and descend diagonally across the anterior surface of the left ventricle.
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The circumflex branch ( Fig. 1.4A,C ) courses toward the left, in the coronary sulcus and onto the base/diaphragmatic surface of the heart, and usually ends before reaching the posterior interventricular sulcus. A large branch, the left marginal artery ( Fig. 1.4A,C ), usually arises from it and continues across the rounded obtuse margin of the heart.
The distribution pattern of the left coronary artery enables it to supply most of the left atrium and left ventricle, and most of the interventricular septum, including the atrioventricular bundle and its branches.
Variations in the distribution patterns of coronary arteries
Several major variations in the basic distribution patterns of the coronary arteries occur:
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The distribution pattern described above for both right and left coronary arteries is the most common and consists of a right dominant coronary artery. This means that the posterior interventricular branch arises from the right coronary artery. The right coronary artery therefore supplies a large portion of the posterior wall of the left ventricle, and the circumflex branch of the left coronary artery is relatively small.
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In contrast, in hearts with a left dominant coronary artery, the posterior interventricular branch arises from an enlarged circumflex branch and supplies most of the posterior wall of the left ventricle ( Fig. 1.5 ).
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Another point of variation relates to the arterial supply to the sinu-atrial and atrioventricular nodes. In most cases, these two structures are supplied by the right coronary artery. However, vessels from the circumflex branch of the left coronary artery occasionally supply these structures.
Aortic arch
The thoracic portion of the aorta can be divided into ascending aorta, arch of the aorta, and thoracic (descending) aorta. Only the arch of the aorta is in the superior mediastinum. It begins when the ascending aorta emerges from the pericardial sac and courses upward, backward, and to the left as it passes through the superior mediastinum, ending on the left side at vertebral level TIV/V ( Fig. 1.6 ). Extending as high as the midlevel of the manubrium of the sternum, the arch is initially anterior and finally lateral to the trachea.
Three branches arise from the superior border of the arch of the aorta; at their origins, all three are crossed anteriorly by the left brachiocephalic vein.
First branch
Beginning on the right, the first branch of the arch of the aorta is the brachiocephalic trunk ( Fig. 1.7 ). It is the largest of the three branches and, at its point of origin behind the manubrium of the sternum, is slightly anterior to the other two branches. The brachiocephalic trunk ascends slightly posteriorly and to the right. At the level of the upper edge of the right sternoclavicular joint, the brachiocephalic trunk divides into:
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the right common carotid artery, and
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the right subclavian artery (see Fig. 1.6 ).
Occasionally, the brachiocephalic trunk has a small branch, the thyroid ima artery, which contributes to the vascular supply of the thyroid gland.
Second branch
The second branch of the arch of the aorta is the left common carotid artery ( Fig. 1.7 ). It arises from the arch immediately to the left and slightly posterior to the brachiocephalic trunk and ascends through the superior mediastinum along the left side of the trachea.
Third branch
The third branch of the arch of the aorta is the left subclavian artery ( Fig. 1.7 ). It arises from the arch of the aorta immediately to the left of, and slightly posterior to, the left common carotid artery and ascends through the superior mediastinum along the left side of the trachea.
Common carotid arteries
The common carotid arteries are the beginning of the carotid system ( Fig. 1.8 ). The right common carotid artery originates from the brachiocephalic trunk immediately posterior to the right sternoclavicular joint and is entirely in the neck throughout its course. The left common carotid artery begins in the thorax as a direct branch of the arch of the aorta and passes superiorly to enter the neck near the left sternoclavicular joint.
Both right and left common carotid arteries ascend through the neck, just lateral to the trachea and esophagus, within a fascial compartment (the carotid sheath). They give off no branches as they pass through the neck.
Near the superior edge of the thyroid cartilage each common carotid artery divides into its two terminal branches—the external and internal carotid arteries ( Fig. 1.9 ).
At the bifurcation, the common carotid artery and the beginning of the internal carotid artery are dilated. This dilation is the carotid sinus ( Fig. 1.10 ) and contains receptors that monitor changes in blood pressure and are innervated by a branch of the glossopharyngeal nerve [IX].
Another accumulation of receptors in the area of the bifurcation is responsible for detecting changes in blood chemistry, primarily oxygen content. This is the carotid body and is innervated by branches from both the glossopharyngeal [IX] and vagus [X] nerves.
Internal carotid arteries
After its origin, the internal carotid artery ascends toward the base of the skull ( Fig. 1.10 ). It gives off no branches in the neck and enters the cranial cavity through the carotid canal in the petrous part of the temporal bone. The internal carotid arteries supply the cerebral hemispheres, the eyes and the contents of the orbits, and the forehead. Branches include the posterior communicating , middle cerebral, and anterior cerebral arteries that supply the brain, and the ophthalmic artery.
Ophthalmic artery
The arterial supply to the structures in the orbit, including the eyeball, is by the ophthalmic artery ( Fig. 1.11 ). This vessel is a branch of the internal carotid artery, given off immediately after the internal carotid artery leaves the cavernous sinus. The ophthalmic artery passes into the orbit through the optic canal with the optic nerve.
In the orbit the ophthalmic artery initially lies inferior and lateral to the optic nerve ( Fig. 1.11 ). As it passes forward in the orbit, it crosses superior to the optic nerve and proceeds anteriorly on the medial side of the orbit.
In the orbit the ophthalmic artery gives off numerous branches as follows:
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the lacrimal artery, which arises from the ophthalmic artery on the lateral side of the optic nerve, and passes anteriorly on the lateral side of the orbit, supplying the lacrimal gland, muscles, the anterior ciliary branch to the eyeball, and the lateral sides of the eyelid;
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the zygomaticofacial and zygomaticotemporal arteries come from the lacrimal branch of the ophthalmic artery ( Fig. 1.12 ), enter the face through the zygomaticofacial and zygomaticotemporal foramina, and supply the area of the face over the zygomatic bone;
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the central retinal artery, which enters the optic nerve, proceeds down the center of the nerve to the retina, and is clearly seen when viewing the retina with an ophthalmoscope—occlusion of this vessel or of the parent artery leads to blindness;
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the long and short posterior ciliary arteries, which are branches that enter the eyeball posteriorly, piercing the sclera, and supplying structures inside the eyeball;
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the muscular arteries, which are branches supplying the intrinsic muscles of the eyeball;
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the supra-orbital artery, which usually arises from the ophthalmic artery immediately after it has crossed the optic nerve, proceeds anteriorly, and exits the orbit through the supra-orbital foramen with the supra-orbital nerve—it supplies the forehead and scalp as it passes across these areas to the vertex of the skull;
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the posterior ethmoidal artery, which exits the orbit through the posterior ethmoidal foramen to supply the ethmoidal cells and nasal cavity;
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the anterior ethmoidal artery, which exits the orbit through the anterior ethmoidal foramen, enters the cranial cavity giving off the anterior meningeal branch, and continues into the nasal cavity supplying the septum and lateral wall, and ending as the dorsal nasal artery;
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the medial palpebral arteries, which are small branches supplying the medial area of the upper and lower eyelids;
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the dorsal nasal artery, which is one of the two terminal branches of the ophthalmic artery, leaves the orbit to supply the upper surface of the nose; and
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the supratrochlear artery, which is the other terminal branch of the ophthalmic artery and leaves the orbit with the supratrochlear nerve, supplying the forehead as it passes across it in a superior direction.
External carotid arteries
The external carotid arteries begin giving off branches immediately after the bifurcation of the common carotid arteries ( Fig. 1.10 and Table 1.1 ). These branches include the superior thyroid artery, ascending pharyngeal artery, lingual artery, facial artery, occipital artery, posterior auricular artery, superficial temporal artery, and maxillary artery.
Table 1.1
Branches of the external carotid artery
| Branch | Supplies |
|---|---|
| Superior thyroid artery | Thyrohyoid muscle, internal structures of the larynx, sternocleidomastoid and cricothyroid muscles, thyroid gland |
| Ascending pharyngeal artery | Pharyngeal constrictors and stylopharyngeus muscle, palate, tonsil, pharyngotympanic tube, meninges in posterior cranial fossa |
| Lingual artery | Muscles of the tongue, palatine tonsil, soft palate, epiglottis, floor of mouth, sublingual gland |
| Facial artery | All structures in the face from the inferior border of the mandible anterior to the masseter muscle to the medial corner of the eye, the soft palate, palatine tonsil, pharyngotympanic tube, submandibular gland |
| Occipital artery | Sternocleidomastoid muscle, meninges in posterior cranial fossa, mastoid cells, deep muscles of the back, posterior scalp |
| Posterior auricular artery | Parotid gland and nearby muscles, external ear and scalp posterior to ear, middle and inner ear structures |
| Superficial temporal artery | Parotid gland and duct, masseter muscle, lateral face, anterior part of external ear, temporalis muscle, parietal and temporal fossae |
| Maxillary artery | External acoustic meatus, lateral and medial surface of tympanic membrane, temporomandibular joint, dura mater on lateral wall of skull and inner table of cranial bones, trigeminal ganglion and dura in vicinity, mylohyoid muscle, mandibular teeth, skin on chin, temporalis muscle, outer table of bones of skull in temporal fossa, structures in infratemporal fossa, maxillary sinus, upper teeth and gingivae, infra-orbital skin, palate, roof of pharynx, nasal cavity |
Superior thyroid artery
The superior thyroid artery is the first branch. It arises from the anterior surface near or at the bifurcation and passes in a downward and forward direction to reach the superior pole of the lateral lobe of the thyroid gland where it gives off the superior laryngeal artery before dividing into the anterior and posterior glandular arteries.
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The superior laryngeal artery originates near the upper margin of the thyroid cartilage and accompanies the internal branch of the superior laryngeal nerve through the thyrohyoid membrane to reach the larynx.
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The anterior glandular branch passes along the superior border of the thyroid gland and anastomoses with its twin from the opposite side across the isthmus ( Fig. 1.13 ).
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The posterior glandular branch passes to the posterior side of the gland and may anastomose with the inferior thyroid artery ( Fig. 1.14 ).
Ascending pharyngeal artery
The ascending pharyngeal artery is the second and smallest branch—it arises from the posterior aspect of the external carotid artery and ascends between the internal carotid artery and the pharynx. The ascending pharyngeal artery supplies the upper part of the pharynx and parts of the palate through a palatine branch. Additionally, a small meningeal branch enters the posterior cranial fossa through the hypoglossal canal, and the terminal branch of the ascending pharyngeal artery is the posterior meningeal artery, which enters the posterior cranial fossa through the jugular foramen.
Lingual artery
The lingual artery arises from the anterior surface of the external carotid artery just above the superior thyroid artery at the level of the hyoid bone, passes deep to the hypoglossal nerve [XII], and passes between the middle constrictor and hyoglossus muscles. The lingual artery supplies the tongue, sublingual gland, gingiva, and the oral mucosa on the floor of the oral cavity.
Facial artery
The facial artery is the third anterior branch of the external carotid artery—it arises just above the lingual artery, passes deep to the stylohyoid and posterior belly of the digastric muscles, continues deep between the submandibular gland and mandible, and emerges over the edge of the mandible just anterior to the masseter muscle, to enter the face. From this point the facial artery runs upward and medially in a tortuous course. It passes along the side of the nose and terminates as the angular artery at the medial corner of the eye.
Along its path the facial artery is deep to the platysma, risorius, and zygomaticus major and minor, superficial to the buccinator and levator anguli oris, and may pass superficially to or through the levator labii superioris.
Branches of the facial artery include the superior and inferior labial branches , lateral nasal branch (see Fig. 1.12 ), and ascending palatine and tonsillar branches .
The labial branches arise near the corner of the mouth:
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The inferior labial branch supplies the lower lip.
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The superior labial branch supplies the upper lip, provides a septal branch to the nasal septum and an alar branch that supplies the region around the lateral aspect of the nose.
Near the midline, the superior and inferior labial branches anastomose with their companion arteries from the opposite side of the face. This provides an important connection between the facial arteries and the external carotid arteries of opposite sides.
The lateral nasal branch is a small branch arising from the facial artery as it passes along the side of the nose. It supplies the lateral surface and dorsum of the nose.
The ascending palatine and tonsillar branches supply the palate, tonsillar regions, and the pharyngeal wall ( Fig. 1.15 ).
Occipital artery
The occipital artery arises from the posterior surface of the external carotid artery, near the level of origin of the facial artery, passes upward and posteriorly deep to the posterior belly of the digastric muscle, and emerges on the posterior aspect of the scalp. Meningeal branches of the occipital artery enter the posterior cranial fossa through the jugular foramen and the mastoid foramen.
Posterior auricular artery
The posterior auricular artery is a small branch arising from the posterior surface of the external carotid artery and passes upward and posteriorly supplying an area of the scalp posterior to the ear.
Superficial temporal artery
The superficial temporal artery is one of the terminal branches and appears as an upward continuation of the external carotid artery. Beginning posterior to the neck of the mandible, it passes anterior to the ear, crosses the zygomatic process of the temporal bone, and above this point divides into anterior and posterior branches that supply the lateral aspect of the scalp. Its single branch is the transverse facial artery.
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The transverse facial artery arises from the superficial temporal artery within the substance of the parotid gland, passes through the gland, and crosses the face in a transverse direction. Lying on the superficial surface of the masseter muscle, it is between the zygomatic arch and the parotid duct.
Maxillary artery
The maxillary artery is the larger of the two terminal branches of the external carotid artery and supplies blood to the nasal cavity, lateral wall and roof of the oral cavity, all the teeth, and the dura mater in the cranial cavity ( Fig. 1.16 ). It originates within the substance of the parotid gland and then passes forward, between the neck of the mandible and sphenomandibular ligament, into the infratemporal fossa. It ascends obliquely through the infratemporal fossa to enter the pterygopalatine fossa by passing through the pterygomaxillary fissure. This part of the vessel may pass either lateral or medial to the lower head of the lateral pterygoid muscle. If it passes medial to the lower head, the maxillary artery then loops laterally between the upper and lower heads of the lateral pterygoid to access the pterygomaxillary fissure.
Branches arise from three parts of the maxillary artery ( Fig. 1.16 ):
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The first part of the maxillary artery (the part between the neck of the mandible and the sphenomandibular ligament) gives origin to two major branches (the middle meningeal and inferior alveolar arteries) and a number of smaller branches (deep auricular , anterior tympanic , and accessory meningeal).
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The second part of the maxillary artery (the part related to the lateral pterygoid muscle) gives origin to deep temporal, masseteric , buccal , and pterygoid branches, which course with branches of the mandibular nerve [V 3 ].
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The third part of the maxillary artery is in the pterygopalatine fossa ( Fig. 1.17 )
Middle meningeal artery
The middle meningeal artery ascends vertically from the maxillary artery and passes through the foramen spinosum to enter the cranial cavity ( Fig. 1.16 ). Just inferior to the foramen spinosum, it passes between the two roots of the auriculotemporal nerve at their origin from the mandibular nerve [V 3 ] ( Fig. 1.16 ). The middle meningeal artery is the largest of the meningeal vessels and supplies much of the dura mater, bone, and related bone marrow of the cranial cavity walls.
Inferior alveolar artery
The inferior alveolar artery descends from the maxillary artery to enter the mandibular foramen and canal with the inferior alveolar nerve ( Fig. 1.16 ). It is distributed with the inferior alveolar nerve and supplies all lower teeth and contributes to the supply of the buccal gingivae. A terminal branch of inferior alveolar artery, the mental artery, enters the face through the mental foramen and supplies the chin and lower lip ( Fig. 1.16 ).
Before entering the mandible, the inferior alveolar artery gives origin to a small mylohyoid branch, which accompanies the nerve to the mylohyoid muscle.
Deep auricular, anterior tympanic, and accessory meningeal arteries
The deep auricular, anterior tympanic, and accessory meningeal arteries are small branches from the first part of the maxillary artery and contribute to the blood supply of the external acoustic meatus, deep surface of the tympanic membrane, and cranial dura mater, respectively.
The accessory meningeal branch also contributes small branches to surrounding muscles in the infratemporal fossa before ascending through the foramen ovale into the cranial cavity to supply the dura mater.
Branches from the second part of the maxillary artery ( Fig. 1.16 )
Deep temporal arteries, usually two in number, originate from the second part of the maxillary artery and travel with the deep temporal nerves to supply the temporalis muscle in the temporal fossa ( Fig. 1.16 ).
Numerous pterygoid arteries also originate from the second part of the maxillary artery and supply the pterygoid muscles.
The masseteric artery, also from the second part of the maxillary artery, accompanies the masseteric nerve laterally through the mandibular notch to supply the masseter muscle.
The buccal artery is distributed with the buccal nerve and supplies skin, muscle, and oral mucosa of the cheek.
Branches from the third part of the maxillary artery in the pterygopalatine fossa (see Fig. 1.17 )
The part of the maxillary artery in the pterygopalatine fossa (the third part) is anterior to the pterygopalatine ganglion and gives origin to branches that accompany branches of the maxillary nerve [V 2 ] and the pterygopalatine ganglion.
Branches include the posterior superior alveolar , infra-orbital , greater palatine, pharyngeal , sphenopalatine , and the artery of the pterygoid canal ( Fig. 1.17 ). Collectively, these branches supply much of the nasal cavity, the roof of the oral cavity, and all upper teeth. In addition, they contribute to the blood supply of the sinuses, oropharynx, and floor of the orbit.
Posterior superior alveolar artery
The posterior superior alveolar artery ( Fig. 1.17 ) originates from the maxillary artery as it passes through the pterygomaxillary fissure. It meets the posterior superior alveolar nerve, accompanies it through the alveolar foramen on the infratemporal surface of the maxilla, and supplies the molar and premolar teeth, adjacent gingiva, and the maxillary sinus.
Infra-orbital artery
The infra-orbital artery ( Fig. 1.17 ) passes forward with the infra-orbital nerve and leaves the pterygopalatine fossa through the inferior orbital fissure. With the infra-orbital nerve, it lies in the infra-orbital groove and infra-orbital canal and emerges through the infra-orbital foramen to supply parts of the face.
Within the infra-orbital canal, the infra-orbital artery gives origin to:
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branches that contribute to the blood supply of structures near the floor of the orbit—the inferior rectus and inferior oblique muscles, and the lacrimal sac; and
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anterior superior alveolar arteries ( Fig. 1.17 ), which supply the incisor and canine teeth and the maxillary sinus.
Greater palatine artery
The greater palatine artery ( Fig. 1.17 ) passes inferiorly with the palatine nerves into the palatine canal. It gives origin to a lesser palatine branch ( Fig. 1.17 ), which passes through the lesser palatine foramen to supply the soft palate, and then continues through the greater palatine foramen to supply the hard palate. The latter vessel passes forward on the inferior surface of the palate to enter the incisive fossa and pass superiorly through the incisive canal to supply the anterior aspect of the septal wall of the nasal cavity.
Pharyngeal branch
The pharyngeal branch ( Fig. 1.17 ) of the maxillary artery travels posteriorly and leaves the pterygopalatine fossa through the palatovaginal canal with the pharyngeal nerve. It supplies the posterior aspect of the roof of the nasal cavity, the sphenoidal sinus, and the pharyngotympanic tube.
Sphenopalatine artery
The sphenopalatine artery ( Fig. 1.17 ) is the terminal branch of the maxillary artery. It leaves the pterygopalatine fossa medially through the sphenopalatine foramen and accompanies the nasal nerves, giving off:
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posterior lateral nasal arteries, which supply the lateral wall of the nasal cavity and contribute to the supply of the paranasal sinuses; and
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posterior septal branches, which travel medially across the roof to supply the nasal septum—the largest of these branches passes anteriorly down the septum to anastomose with the end of the greater palatine artery.
Artery of pterygoid canal ( Fig. 1.17 )
The artery of the pterygoid canal passes posteriorly into the pterygoid canal. It supplies surrounding tissues and terminates, after passing inferiorly through cartilage filling the foramen lacerum, in the mucosa of the nasopharynx.
Subclavian arteries
The subclavian arteries on both sides arch upward out of the thorax to enter the root of the neck ( Fig. 1.18 ).
The right subclavian artery begins posterior to the sternoclavicular joint as one of two terminal branches of the brachiocephalic trunk. It arches superiorly and laterally to pass anterior to the extension of the pleural cavity in the root of the neck and posterior to the anterior scalene muscle. Continuing laterally across rib I, it becomes the axillary artery as it crosses its lateral border.
The left subclavian artery begins lower in the thorax than the right subclavian artery as a direct branch of the arch of the aorta. Lying posterior to the left common carotid artery and lateral to the trachea, it ascends and arches laterally, passing anterior to the extension of the pleural cavity and posterior to the anterior scalene muscle. It continues laterally over rib I, and becomes the axillary artery as it crosses the lateral border of rib I.
Both subclavian arteries are divided into three parts by the anterior scalene muscle ( Fig. 1.18 ):
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The first part extends from the origin of the artery to the medial border of the anterior scalene muscle.
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The second part is the part of the artery posterior to the anterior scalene and anterior to the middle scalene muscles.
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The third part extends from the lateral border of the anterior scalene muscle to the lateral border of rib I. At this point it becomes the axillary artery.
All branches from the right and left subclavian arteries arise from the first part of the artery, except in the case of one branch (the costocervical trunk) on the right side ( Fig. 1.18 ). The branches include the vertebral artery, the thyrocervical trunk, the internal thoracic artery, and the costocervical trunk.
Vertebral artery
The vertebral artery arises from the first part of the subclavian artery as it enters the root of the neck ( Fig. 1.18 ). A large branch, arising from the first part of the subclavian artery medial to the anterior scalene muscle, it ascends and enters the foramen in the transverse process of vertebra CVI. Continuing to pass superiorly, the vertebral artery passes through the foramina of vertebrae CV to CI. At the superior border of vertebra CI, the artery turns medially and crosses the posterior arch of vertebra CI. From here it passes through the foramen magnum to enter the posterior cranial fossa. On entering the cranial cavity through the foramen magnum each vertebral artery gives off a small meningeal branch.
Continuing forward, the vertebral artery gives rise to three additional branches before joining with its companion vessel to form the basilar artery ( Figs. 1.19 and 1.20 ):
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One branch joins with its companion from the other side to form the single anterior spinal artery, which then descends in the anterior median fissure of the spinal cord.
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A second branch is the posterior spinal artery, which passes posteriorly around the medulla and then descends on the posterior surface of the spinal cord in the area of the attachment of the posterior roots—there are two posterior spinal arteries, one on each side (although the posterior spinal arteries can originate directly from the vertebral arteries, they more commonly branch from the posterior inferior cerebellar arteries).
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Just before the two vertebral arteries join, each gives off a posterior inferior cerebellar artery.
The basilar artery travels in a rostral direction along the anterior aspect of the pons ( Fig. 1.20 ). Its branches in a caudal to rostral direction include the anterior inferior cerebellar arteries, several small pontine arteries, and the superior cerebellar arteries. The basilar artery ends as a bifurcation, giving rise to two posterior cerebral arteries.
Thyrocervical trunk
The second branch of the subclavian artery is the thyrocervical trunk ( Fig. 1.18 ). It arises from the first part of the subclavian artery medial to the anterior scalene muscle, and divides into three branches—the inferior thyroid, the transverse cervical, and the suprascapular arteries.
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