serratus anterior /serā″təs/ [L, serra, saw teeth] , a thin muscle of the chest wall extending from the ribs under the arm to the scapula. Arising from the outer surface and upper border of the first eight or nine ribs, it inserts into the medial angle, the vertebral border, and the inferior angle of the scapula. It acts to rotate the scapula and to raise the shoulder, as in full flexion and abduction of the arm. Compare pectoralis major, pectoralis minor, subclavius.
