The number of attachments varies; a slip may extend to the occipital or mastoid, to the trapezius, scalene or serratus anterior, or to the first or second rib. The muscle may be subdivided into several distinct parts from origin to insertion. Levator claviculæ from the transverse processes of one or two upper cervical vertebræ to the outer end of the clavicle corresponds to a muscle of lower animals. More or less union with the serratus anterior muscle.
Nerve supply
The levator scapulae is supplied by two or three branches of the fourth and fifth cervical nerves, and frequently by a branch from the dorsal scapular nerve.
Blood supply
The levator scapulae is supplied by the dorsal scapular artery. Normally, this artery has a small branch which passes laterally to the supraspinatus fossa of the scapula, and in a third of cases, this branch supplies the muscle. If the dorsal scapular artery comes off the transverse cervical artery, the parent transverse cervical artery splits, the dorsal scapular artery passes medially, while the transverse cervical artery passes laterally.
Function
When the spine is fixed, levator scapulae elevates the scapula and rotates its inferior angle medially. It often works in combination with other muscles like the rhomboids and pectoralis minor to rotate down. Elevating or rotating one shoulder at a time would require muscles to stabilize the cervical spine and keep it immobile so it does not flex or rotate. Elevating both at once with equal amounts of pull on both side of cervical spinal origins would counteract these forces. Downward rotation would be prevented by co-contraction of other muscles that elevate the spine, the upper fibers of the trapezius, which is an upward rotator. When the shoulder is fixed, levator scapulae rotates to the same side and flexes the cervical spine laterally. When both shoulders are fixed, a simultaneous co-contraction of both levator scapulae muscles in equal amounts would not produce lateral flexion or rotation, and may produce straight flexion or extension of the cervical spine.
Other animals
The muscles of the shoulder can be categorized into three topographic units: the scapulohumeral, axiohumeral, and axioscapular groups. Levator scapulae forms part of the latter group together with rhomboid major, rhomboid minor, serratus anterior, and trapezius. The trapezius evolved separately, but the other three muscles in this group evolved from the first eight or ten ribs and the transverse processes of the cervical vertebrae. The serratus anterior formed the basal unit for these three muscles. In higher primates it has evolved into two separate muscles — serratus anterior and levator scapulae — by concentration of the proximal and distal fibers and progressive reduction of the intermediate fibers. The fibers concerned with the cranial displacement of the scapula became the levator scapulae.
