Dalley, 10th Edition

Chapter 2 ■ Back

118

Extrinsic Back Muscles The super cial extrinsic back muscles (trapezius, latis simus dorsi, levator scapulae, and rhomboids) are posterior axioappendicular muscles that connect the axial skeleton (vertebral column) with the superior appendicular skeleton (pectoral girdle and humerus) and produce and control limb movements (Fig. 2.32A; see Table 3.5 in Chapter 3, Upper Limb). Although located in the back region, for the most part these muscles receive their nerve supply from the

anterior rami of cervical nerves and act on the upper limb. The trapezius receives its motor bers from a cranial nerve, the spinal accessory nerve (CN XI). The intermediate extrinsic back muscles (serratus posterior) are thin, weak muscles, commonly designated as super cial respiratory muscles, but are more likely proprio ceptive rather than motor in function (Vilensky et al., 2001). They are described with muscles of the thoracic wall (see Chapter 4, Thorax). The serratus posterior superior lies deep to the rhomboid muscles, and the serratus posterior

Descending (superior) part of trapezius Levator scapulae Rhomboid minor Rhomboid major

Cutaneous branches of posterior rami Transverse (middle) part of trapezius

Ascending (inferior) part of trapezius

Triangle of auscultation

Spinal accessory nerve (CN XI)

Cutaneous branches of posterior rami

Trapezius

Latissimus dorsi

Posterior branch of lateral cutaneous nerves

External oblique

Thoracolumbar fascia

Lateral cutaneous branch of iliohypogastric nerve (branch of L1)

Cutaneous branches of posterior rami of L1 to L3

(A) Posterior view

Layers of anterolateral abdominal wall muscle: Copyright © 2027 Wolters Kluwer. Unauthorized reproduction of the article is prohibited.

Origin of (2) & (3) from lateral part of thoracolumbar fascia

Psoas major muscle Quadratus lumborum Thoracolumbar fascia: Anterior layer

(1) External oblique (2) Internal oblique (3) Transversus abdominis

Free posterior border of external oblique (1)

Middle layer Posterior layer

Latissimus dorsi

Deep muscles of back

(B) Transverse section, posterolateral abdominal wall

FIGURE 2.32. Muscles of back. A. The super cial extrinsic muscles. The trapezius is re ected on the left to show the spinal accessory nerve (CN XI), coursing on its deep surface, and the levator scapulae and rhomboid muscles. B. This transverse section of part of the back shows the location of the intrinsic back muscles and the layers of fascia associated with them (thoracolumbar fascia, purple ).