Serratus anterior muscle

Origin Serratus anterior typically originates by ten muscle slips – arising from the 1st to 9th ribs; because two slips arise from the 2nd rib, the number of slips is greater than the number of ribs from which they originate. Insertion The muscle is inserted along the medial border of the scapula between the superior and inferior angle of the scapula. The muscle is divided into three parts according to the points of insertion: The long thoracic nerve travels inferiorly on the surface of the serratus anterior muscle. Relations The serratus anterior lies deep to the subscapularis, from which it is separated by the subscapularis (supraserratus) bursa. It is separated from the rib by the scapulothoracic (infraserratus) bursa. ==Function==

All three parts described above pull the scapula forward around the thorax, which is essential for anteversion of the arm. As such, the muscle is an antagonist to the rhomboids. However, when the inferior and superior parts act together, they keep the scapula pressed against the thorax together with the rhomboids and therefore these parts also act as synergists to the rhomboids. The inferior part can pull the lower end of the scapula laterally and forward and thus rotates the scapula to make elevation of the arm possible. Additionally, all three parts can lift the ribs when the shoulder girdle is fixed, and thus assist in respiration. because it is largely responsible for the protraction of the scapula—that is, the pulling of the scapula forward and around the rib cage that occurs when someone throws a punch. The serratus anterior acts in concert with the upper and lower fibers of the trapezius muscle to sustain upward rotation of the scapula, which allows for overhead lifting. == Clinical significance ==

The long thoracic nerve that supplies the serratus anterior muscle is vulnerable during certain types of surgery (for example, during lymph node clearance from the axilla for breast cancer). Damage to this nerve is the most common cause of winged scapula. ==Other animals==

The muscles of the shoulder can be categorized into three topographic units: the scapulohumeral, axiohumeral, and axioscapular groups. Serratus anterior forms part of the latter group together with rhomboid major, rhomboid minor, levator scapulae, 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 (homologous to the ribs). Functional demands have resulted in the evolution of individual muscles from the basal unit formed by the serratus anterior. In primitive tetrapods, the main function of the axioscapular group is to control the movements of the vertebral border of the scapula: fibers concerned with the dorsal movement of scapula evolved into the rhomboids, those with ventral motion into serratus anterior, and those with cranial movements into levator scapulae. The evolution of the serratus anterior itself has resulted in (1) grouping of its distal and proximal fibers, (2) size reduction of its intermediate fibers, and (3) the insertion of its dominant superior and inferior parts onto the superior and inferior angles of the scapula. ==Additional images==