The teres major muscle is a functional extension of the subscapularis muscle which lies superiorly on each side. It arises from the oval area on the dorsal surface of the scapula around its inferior angle. Its fibres run superolaterally to insert into the medial lip of the intertubercular groove of the humerus. On route, the tendon of latissimus dorsi winds around its inferior border. Together, teres major and latissimus dorsi form the posterior axillary fold.
Teres major is supplied by the lower subscapular nerve from the posterior cord of the brachial plexus (C5, C6). This enters the muscle anteriorly.
It has several actions:
- acting alone: adducts and medially rotates humerus at the glenohumeral joint
- assists in extending the flexed arm
- acts as an antagonist in abduction of the humerus
- stabilises shoulder joint in conjunction with other muscles
- with the arm fixed, acts with pectoralis major to pull the trunk superiorly
Teres major bounds both the quadrangular and triangular spaces.