Teres major is an offspring of subscapularis. It has migrated around to the dorsal surface of the scapula, where it arises from an oval area on the lateral side of the inferior angle. It runs edge to edge with the lower border of its parent subscapularis, and is inserted in continuity with it into the medial lip of the intertubercular groove. The ribbon-like tendon of latissimus dorsi winds around its lower border and comes to lie in front-of the upper part of the muscle at its insertion.
Nerve supply of Teres major:
By the lower subscapular nerve (C6 and 7), which supplies its parent subscapularis, and lies in the angle between the subscapular and circumflex scapular arteries, entering the anterior surface of the muscle.
Action of Teres major:
It assists the other short muscles in steadying the upper end of the humerus in movements at the periphery of the limb; acting alone it is an adductor and medial rotator of the humerus at the shoulder joint. With teres minor it holds down the upper end of the humerus as deltoid pulls up the bone into abduction.