Download D2-1 UNIT 2. DISSECTION: SUPERFICIAL MUSCLES OF THE

UNIT 2.
DISSECTION:
SUPERFICIAL MUSCLES OF THE BACK
STRUCTURES TO IDENTIFY:
External occipital protuberance
Mastoid process
Spinous processes (vertebra prominens)
Ligamentum nuchae
Sacrum
Crest of the ilium
Scapula
Dorsal rami
Greater occipital nerve
Occipital artery
Trapezius
Latissimus dorsi
Thoracolumbar fascia
Spinal Accessory Nerve
Transverse Cervical Artery
Cervical nerves 3 and 4
Thoracodorsal nerve and artery
Levator scapulae
Rhomboideous minor
Rhomboideous major
Dorsal scapular nerve and artery
DISSECTION INSTRUCTIONS:
1. Certain surface points should be identified before the skin is reflected. In the midline
at the base of the skull is the external occipital protuberance. Laterally, behind the
ear, is the mastoid process. Between the external occipital protuberance and the
mastoid process on each side is the superior nuchal line. In the midline of the back,
the spinous processes of most of the vertebrae may be palpated. The most superior
vertebral spine that is palpable is that of the seventh cervical vertebra (vertebra
prominens). The upper cervical spines are covered by the ligamentum nuchae that
extends from the external occipital protuberance to the seventh cervical spine. Locate
the vertebral border of the scapula. Running laterally and upward from this border at
the level of the third thoracic spine is the spine of the scapula. The spine ends
laterally as the broad acromion process, the bony prominence of the shoulder.
Inferior to the last lumbar vertebra the posterior surface of the sacrum is palpable, and
below it, between the buttocks, is the coccyx. Identify the crest of the ilium arching
laterally from the sacrum.
2. Make the following incisions through the skin (Using Figure 1).
•
First incision: a midline incision from the external occipital protuberance to the
coccyx.
•
Second incision: from the upper end of the first incision, one laterally and
downward across the back of the head to the mastoid process.
•
Third incision:
process.
From the seventh cervical spine laterally to the acromion
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•
Fourth incision: (in the lumbar region) from the first incision upward and
laterally to the back of the arm.
•
Fifth incision: From the lower end of the first incision, upward and laterally
along the crest of the ilium.
Figure 1
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3. Reflect the skin and expose the superficial fascia of the back. Before removing the
superficial fascia, dissect some of the cutaneous nerves of the back (N. plate 177 and
G. plate 4.31). These nerves are derived from dorsal rami of cervical, thoracic and
lumbar spinal nerves. With the exception of the greater occipital nerve, they are
small and are usually accompanied by an artery and vein (Figure 2).
Figure 2
4. The most superficial muscles of the back are the trapezius and the latissimus dorsi (N.
plate 174, 177; G. plate 4.31). Remove the superficial and deep fascia covering the
trapezius and expose the muscle fibers. As you clean the upper fibers of the muscle,
which are attached to the head, secure the greater occipital nerve. This large,
cutaneous nerve is the terminal part of the dorsal ramus of the second cervical nerve.
It pierces the trapezius an inch lateral and an inch below the external occipital
protuberance and runs upward to be distributed to the back of the scalp. It is
accompanied in its distribution by the occipital artery (N. plate 178; G. plate 4.31,
4.38 and 4.39).
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The trapezius is a flat, triangular muscle that arises from the medial third of the
superior nuchal line, the entire length of the ligamentum nuchae and the spinous
process of all 12 thoracic vertebrae. Its fibers converge laterally to a V-shaped
insertion on the posterior border of the lateral third of the clavicle, the medial border
of the acromion and the upper border of the scapular spine.
5. Clean the latissimus dorsi (N. plate 174, 177; G. plate 4.31). In removing the
superficial fascia from the region just lateral to the lumbar spines, avoid cutting
through or removing the deep fascia, here known as the thoracolumbar fascia. It is
recognized by the glistening aponeurotic appearance of its external surface. It is
attached medially to the lumbar spine and the sacrum. The thoracolumbar fascia
differs from the deep fascia that is ordinarily found surrounding muscles in that it is
very dense. I the lumbar region of the back, it is arranged in two layers (lamellae)
between which the deep muscles of the are enclosed. The glistening sheet is the
more superficial of these layers (posterior lamella) and must be cleaned at the same
time as the latissimus dorsi, since it serves as part of the origin of the latissimus.
The latissimus dorsi is a broad, flat muscle that covers the lower lateral part of the
back. The lowest part of the trapezius is superficial to it. It has a large origin from
the spinous processes of the lower 5 or 6 thoracic vertebrae, the posterior lamella
of the thoracolumbar fascia, the crest of the ilium and the lower three or four
ribs. Sometimes it also takes an origin from the inferior end of the scapula. The
fibers converge upward and laterally insert into the intertubercular sulcus on the
anterior surface of the humerus. We will not see its insertion. Close to the tendon
(deep surface) the muscle receives its neurovascular bundle (thoracodorsal nerve and
artery).
6. The trapezius should now be reflected to allow access to underlying structures (N.
plates 174, 177; G plate 4.31). Pass your hand deep to the inferior and lateral border
of the muscle. You are separating the trapezius from other muscles. Starting
inferiorly, cut the muscle from its origin all the way to the external occipital
protuberance. Now detach the upper fibers of the trapezius from the occipital bone
and reflect the muscle laterally to its insertion. As it is turned laterally, the nerves and
vessels (spinal accessory nerve and the superficial branch of the transverse cervical
artery) that supply the trapezius will be found on its deep surface. The trapezius is
also innervated by the third and fourth cervical nerves. (ventral primary rami of C3
and C4) (N. plate 177; G. plate 4.31).
7. Now clean the three remaining superficial muscles: levator scapulae, rhomboideous
major and rhomboideous minor (N. plate 174, 177; G. plate 4.31, 4.32). All three
muscles insert on the vertebral border of the scapula. Clean the two rhomboid
muscles (these muscles may be fused). The rhomboideous minor is a narrow, flat
muscle taking origin from the ligamentum nuchae and the spinous process of C7.
Its fibers insert into the vertebral border of the scapula opposite the scapular
spine. The rhomboideous major is a much wider, flat muscle immediately inferior
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to minor. It takes origin from the upper four or five thoracic spines and inserts into
the vertebral border of the scapula below the scapular spine.
Clean the levator scapulae. This muscle arises by four slips from the posterior
tubercles of the transverse processes of the upper four cervical vertebrae. It
inserts into the vertebral border of the scapula above the spine.
Make a vertical incision through both the rhomboid muscles just lateral to their origin
and reflect them. (Do NOT cut levator scapulae.) As the muscles are being reflected
clean the dorsal scapular nerve and the deep branch of the transverse cervical artery.
They descend slightly medial to the vertebral border of the scapula and deep to the
levator scapulae and the two rhomboids. The dorsal scapular nerve is the nerve
supply to both rhomboids and sometimes to the levator scapulae, which is supplied
chiefly by the third and fourth cervical nerves (ventral primary rami of C3 and C4).
Figure 3
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