On each side, serratus anterior is a large, broad sheet-like muscle which runs from thorax to scapula. Serratus in Latin means saw-like, the appearance of the anterior origin of the muscle.
It originates from several sites on the outer aspects of the first eight – occasionally nine – ribs between their respective angles and costal cartilages. The first ‘digitation’ or muscular slip is anomalous in that it arises from both the first and second ribs. The remaining digitations arise from a single rib and the intervening intercostal fascia. The lowest four digitations are interrupted by the costal attachments of the external oblique muscle of the abdomen.
All the digitations pass posteriorly over the side of the thorax. They cover the medial wall of the axilla then deep to the scapula to insert into its medial border. The upper two digitations fuse to insert into the upper angle of the scapula along this line; the lower four digitations converge on the inferior angle; the intermediate digitations insert into the intermediate space. Mobile fascia is sited both superficial and deep to the muscle to permit free movement.
Serratus anterior is innervated by the long thoracic nerve (C5, C6, C7); nerve damage or muscular weakness may cause a winged scapula.
It has a variety of functions, the most important of which are protraction and lateral rotation of the scapula.