The Lats Muscles of the posterior trunk (“back” muscles) The muscles of the posterior trunk are organized into three layers: superficial, intermediate, and deep. Muscles in the superficial layer include the trapezius, latissimus dorsi, rhomboids, levator scapula, and serratus anterior. The trapezius and latissimus dorsi are most superficial, followed by the deeper rhomboids and levator scapula. The serratus anterior muscle is located more laterally on the thorax. In general, bilateral activation of the muscles of the superficial layer extends the adjacent region of the axial skeleton. Unilateral activation, however, laterally flexes and, in most cases, axially rotates the region. The right middle trapezius, for example, assists with right lateral flexion and left axial rotation of the upper thoracic region. Muscles within the superficial and intermediate layers of the back are often referred to as “extrinsic” because, from an embryologic perspective, they were originally associated with the front “limb buds” and only later in their development migrated dorsally to their final position on the back. Although muscles such as the levator scapula, rhomboids, and serratus anterior are located within the back, technically they belong with upper limb muscles.
The Anatomy Latissimus Dorsi Proximal attachments: posterior layer of the thoracolumbar fascia, spinous processes and supraspinous ligaments of the lower half of the thoracic vertebrae and all lumbar vertebrae, median sacral crest, posterior crest of the ilium, lower four ribs, small area near the inferior angle of the scapula, and muscular interdigitations from the obliquus external abdominis See image 1,3,4 Distal attachment: floor of the intertubercular groove of the humerus. See image 4
IMAGE 1