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Muscles of the Back and Scapula


Atlas References *

* NOTE: This dissection guide is cross-referenced to the following atlases: Netter, Atlas of Human Anatomy, ed 7 (Netter); McMinn's Clinical Atlas of Human Anatomy , ed 7 (McMinn); and Gray's Atlas of Anatomy, ed 2 (Gray's). Page references from each atlas are provided at the beginning of 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 2 , 27 , 28 , 29 to give you the opportunity to study the relevant anatomy in depth to aid in your dissection.

  • Netter: 180–183, 257, 413–418

  • McMinn: 101–103, 131–136, 144

  • Gray's Atlas: 20–32, 36–42, 399, 400

Before You Begin

Make sure that you have palpated the following anatomic landmarks on yourself and classmates:

  • Superior nuchal line

  • External occipital protuberance (inion)

  • Mastoid process

  • Spinous process of the 7th cervical vertebra (C7, vertebra prominens)

  • Spinous process of the thoracic and lumbar vertebrae, the sacrum, and the coccyx

  • Medial and lateral parts of the clavicles

  • Iliac crests

  • Trapezius muscle

  • Latissimus dorsi muscle

  • Deltoid muscle

  • Triceps brachii muscle

  • Acromion

Skin and Superficial Fascia

  • o

    Begin by palpating bony landmarks. With a marker, draw the following lines on the skin of the cadaver ( Fig. 2.1 ):

    • 1.

      From the external occipital protuberance, down the midline of the back to the sacrum.

    • 2.

      Laterally, from the external occipital protuberance to the mastoid process on each side of the cadaver.

    • 3.

      Laterally, from the spinous process of the vertebra prominens to the acromion of each shoulder.

    • 4.

      Superiorly from the sacrum, curving obliquely over the iliac crests to the midaxillary line on each side of the body; that is, to a point about halfway around the upper edge of each iliac crest.

    Fig. 2.1, Skin markings for incision lines: neck and back.

  • o

    Incise the skin along the lines just described, beginning at the point where the incisions for the midline and from the shoulders meet ( Fig. 2.2 ).

    Fig. 2.2, Reflection of skin from superficial fascia.

  • o

    Retract the skin carefully (with toothed forceps), leaving the fat (superficial fascia) intact (see Fig. 2.2 ).

Dissection Tip

Place absorptive cloths at the inferolateral spaces of the iliac crest. Excessive amounts of embalming fluid often accumulate at this location.

Dissection Tip

Make necessary “buttonholes” in the skin to facilitate the dissection ( Fig. 2.3 ), as indicated in Chapter 1 .

Fig. 2.3, Make “buttonholes” in the skin to facilitate its reflection from the superficial fascia.

  • o

    On one side of the body, the dissectors should first reflect only the skin, leaving the superficial fascia (tela subcutanea) in place.

  • o

    Start the separation of the superficial fascia from the underlying deep fascia in the midline, by identifying a small part of the trapezius muscle .

  • o

    Carefully scrape off the superficial fascia from the surface of the muscle with your scalpel ( Fig. 2.4 ).

    Fig. 2.4, Deep skin incisions showing deep fascia and muscle fibers.

Dissection Tip

As the superficial fascia is reflected, watch for the passage of neurovascular bundles from the deep fascia into the deep surface of the superficial fascia. Save short segments of several of these for later demonstration and review.

Dissection Tip

Take precautions to avoid cutting too deeply with the scalpel. In some cadavers, the superficial fascia is very thin, and more deeply situated structures can be cut and destroyed ( Figs. 2.5 and 2.6 ).

Fig. 2.5, Reflection of deep fascia and appearance of trapezius, latissimus dorsi, and thoracolumbar fascia.

Fig. 2.6, Note possible differences in thickness of the skin and fascia. Avoid cutting too deeply with the scalpel to prevent damage to superficial structures when exposing them.

  • o

    Completely remove superficial fascia over the latissimus dorsi muscle.

  • o

    On the other side of the body, the skin and superficial fascia can be reflected together.

Dissection Tip

Care must be taken in this latter approach to avoid damage to the underlying muscles, especially the trapezius and latissimus dorsi muscles and their aponeuroses. Identify these before the skin and fascia are reflected more than a few centimeters.

Superficial Muscles of the Back: Part 1

  • o

    Remove enough deep fascia to clarify the borders of the two most superficial muscles of the back, the trapezius and latissimus dorsi ( Fig. 2.7 ).

    Fig. 2.7, Complete removal of superficial fascia over trapezius, latissimus dorsi, and posterior layer of thoracolumbar fascia on left side of cadaver. Deep fascia and some adipose tissue have been left intact on right side.

Anatomy Note

Note the diamond-shaped aponeurotic area of the trapezius at the upper middle thoracic region (see Fig. 2.7 ). The skin, superficial fascia, and deep fascia are relatively thin here. This is in contrast to the lateral lumbar region, where the amount of subcutaneous fat is increased (see Fig. 2.6 ).

  • o

    Identify the teres major muscle and the infraspinous fascia (see Fig. 2.7 ).

Anatomy Note

This fascia covering the infraspinatus muscle is attached to the margins of the infraspinous fossa and is continuous with the deltoid fascia along the posterior border of the muscle.

  • o

    Carefully separate the deep fascia covering the trapezius muscle ( Fig. 2.8 ).

    Fig. 2.8, Careful separation of deep fascia covering trapezius muscle.

  • o

    While cleaning away the fascia that overlies the most cranial portion of the trapezius ( Figs. 2.9 and 2.10 ), look for the greater occipital nerve .

    Fig. 2.9, Exposure of superior part of trapezius with portions of deep fascia still covering its uppermost portion.

    Fig. 2.10, Exposure of deep fascia covering the upper portion of trapezius.

  • o

    This nerve usually can be found approximately 1 inch (2.5 cm) from the midline and 1 inch inferior to the superior nuchal line, as the nerve pierces the trapezius ( Figs. 2.11 and 2.12 ).

    Fig. 2.11, After identifying the greater occipital nerve, separate and remove the deep fascia; M, midline; H, horizontal line.

    Fig. 2.12, Deep fascia is cut, and the greater occipital nerve and occipital artery are visible.

  • o

    Also at this location, locate the occipital artery , and preserve it as the trapezius is reflected (see Fig. 2.12 ).

Dissection Tip

Greater Occipital Nerve

To identify the greater occipital nerve, draw a horizontal imaginary line from the external occipital protuberance to the mastoid process. At 3 cm lateral to the external occipital protuberance on the imaginary line, remove the deep fascia to identify this nerve.

3rd Occipital Nerve

Usually the deep fascia over the trapezius muscle below the superior nuchal line is very thick and difficult to cut until the 7th cervical vertebra (C7) level. Pay special attention to the dissection process. Intermingled with the deep fascia over this area is the 3rd occipital nerve; try to expose and save it ( Fig. 2.13 ).

Fig. 2.13, Complete exposure and detachment of the superior part of the trapezius from the deep fascia. Observe the 3rd occipital nerve.

  • o

    To detach the trapezius from its origin, first make a small vertical cut through the lower part of the trapezius at the 12th thoracic vertebra (T12) level as it attaches to the midline.

  • o

    Continue the incision to the external occipital protuberance. Define and loosen the trapezius with your fingers or with scissors before you proceed further upward along the midline ( Fig. 2.14 ).

    Fig. 2.14, Dissection of lateral trapezius muscle facilitated by a separation technique using dissecting scissors.

  • o

    Detach the trapezius from its origin on the superior nuchal line and the external occipital protuberance, and sever the fibers that arise from the spines and associated ligaments of the cervical and thoracic vertebrae. Reflect the trapezius laterally toward its insertion onto the scapula ( Fig. 2.15 ).

    Fig. 2.15, Separation of the connective tissue on the deep surface of trapezius.

  • o

    On the deep surface of the trapezius, near the superior angle of the scapula, look for the nerve that supplies the trapezius, the accessory nerve .

  • o

    Note the artery that supplies the trapezius muscle, the ascending branch of the transverse cervical artery .

  • o

    Identify the levator scapulae , rhomboid minor and major muscles , and neurovascular bundle ( Fig. 2.16 ).

    Fig. 2.16, Complete reflection of the trapezius and appearance of the underlying levator scapulae and rhomboid muscles, and neuromuscular bundle.

  • o

    Clean the fascia from these muscles so that their fibers can be seen clearly.

  • o

    Gently retract the levator scapulae muscle medially. At the midpoint of the levator, you will see the accessory nerve exit and run on the internal surface of the trapezius muscle ( Figs. 2.17 and 2.18 ).

    Fig. 2.17, Identification of accessory nerve, emerging deep from medial side at midpoint of levator scapulae muscle.

    Fig. 2.18, Careful separation of neurovascular bundle to identify accessory nerve, ascending branch of transverse cervical artery, and tributaries of transverse cervical vein.

  • o

    Carefully separate the neurovascular bundle to identify the accessory nerve, ascending branch of the transverse cervical artery, and tributaries of transverse cervical vein ( Figs. 2.19 and 2.20 ).

    Fig. 2.19, After careful dissection of connective tissue, trapezius muscle is reflected and accessory nerve identified.

    Fig. 2.20, Trapezius muscle is reflected and the accessory nerve identified.

  • o

    Carefully expose the deep fascia over the rhomboid major and minor muscles. In some specimens the line of cleavage between the rhomboid muscles may be unclear ( Figs. 2.21 and 2.22 ).

    Fig. 2.21, Carefully expose deep fascia over the rhomboid major and minor muscles.

    Fig. 2.22, Trapezius and latissimus dorsi muscles are reflected. Underlying intermediate extrinsic muscles of the back are exposed.

  • o

    Reflect the rhomboid muscles laterally toward their insertion onto the medial border of the scapula ( Fig. 2.23 ) ( Plate 2.1 ).

    Fig. 2.23, After the trapezius is exposed, reflect the rhomboid major and minor muscles carefully to expose the serratus posterior superior.

    Plate 2.1, Superficial musculature of the back.

  • o

    Deep to the rhomboids, identify the serratus posterior superior muscle, which inserts onto the ribs rather than onto the scapula. (This fact will assist you in its identification.)

  • o

    On the deep surface of the rhomboids, try to identify the dorsal scapular nerve and dorsal scapular artery ( Fig. 2.24 ).

    Fig. 2.24, View of deep surface of scapula illustrating dorsal scapular artery and nerve running at the medial border of scapula.

Anatomy Note

The dorsal scapular nerve innervates the rhomboid and levator scapulae muscles (in addition to branches from C3 and C4). The dorsal scapular nerve arises from C5, one of the two nerves that arise directly from the ventral rami of the brachial plexus.

Anatomy Note

In about 50% of the specimens, the dorsal scapular artery is absent, and the deep branch of the transverse cervical artery replaces it. The dorsal scapular artery typically arises from the 3rd part of the subclavian artery and runs posteriorly through the brachial plexus.

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