Dalley, 10th Edition

119

Muscles of Back

inferior lies deep to the latissimus dorsi. Both serratus mus cles are innervated by intercostal nerves, the superior by the rst four intercostals and the inferior by the last four. Intrinsic Back Muscles The intrinsic back muscles ( muscles of back proper , deep back muscles ) are innervated by the posterior rami of spi nal nerves and act to maintain posture and control move ments of the vertebral column (Figs. 2.32B and 2.33). These muscles, which extend from the pelvis to the cranium, are enclosed by deep fascia that attaches medially to the nuchal

ligament (Figs. 2.33 and 2.34), the tips of the spinous pro cesses of the vertebrae, the supraspinous ligament, and the median crest of the sacrum. The fascia attaches laterally to the cervical and lumbar transverse processes and the angles of the ribs. The thoracic and lumbar parts of the deep fascia constitute the thoracolumbar fascia (Fig. 2.32). It extends laterally from the spinous processes and forms a thin cover ing over the intrinsic back muscles in the thoracic region and a strong thick covering for muscles in the lumbar region. The intrinsic back muscles are grouped into super cial, in termediate, and deep layers according to their relationship to the surface.

2

Nuchal ligament

Semispinalis capitis

Sternocleidomastoid (SCM)

Sternocleidomastoid

*

Splenius capitis

Levator scapulae

Levator scapulae

*

Splenius cervicis

Angles of 3rd–5th ribs

Iliocostalis cervicis

Spinalis thoracis

Longissimus thoracis

Longissimus

Iliocostalis thoracis

Intermediate layer of intrinsic back muscles—erector spinae

Iliocostalis

Posterior rami

10th rib

Iliocostalis lumborum

Aponeurosis of transversus abdominis

Superficial layer of intrinsic back muscles *

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Gluteal fascia overlying gluteus medius

Gluteus maximus

Posterior view

FIGURE 2.33. Super cial and intermediate layers of intrinsic back muscles: splenius and erector spinae. The sternocleidomastoid (SCM) and levator scapulae muscles are re ected to reveal the splenius capitis and splenius cervicis muscles. On the right side, the erector spinae is undisturbed (in situ) and shows the three columns of this massive muscle. On the left side, the spinalis muscle, the thinnest and most medial of the erector spinae columns, is displayed as a separate muscle by re ecting the longissimus and iliocostalis columns of the erector spinae. As they ascend, the direction of bers is different in the three main groups of muscles: The super cial (splenius) muscles run from medial to lateral, the intermediate (erector spinae) muscles run mostly vertically, and the deep (transversospinalis) muscles run mainly from lateral to medial (see Fig. 2.36).