Corpus: Teres major muscle

The teres major muscle originates from the lower angle (Angulus inferior) of the scapula.

Its fibers run cranially and laterally, ending in an about 5 cm long tendon that attaches to the crest of the lesser tubercle of the humerus, behind the insertion of the latissimus dorsi muscle.

Anatomically, it defines the medial and lateral axillary space.

The innervation of the teres major muscle is provided by the thoracodorsal nerve from the brachial plexus (segments: C6-C7) or by the subscapular nerves (segments: C5-C6).

The teres major muscle is responsible for the internal rotation, adduction, and retroversion of the upper arm, supporting the latissimus dorsi muscle. Its main function is the retroversion of the arm medially. This movement is particularly well controlled by the muscle when the arm is initially in an anteversion and slight abduction position.

Illustratively, this means the muscle is needed to cross the arms behind the back (apron grip). However, for the backward movement of the arms, the posterior part of the deltoid muscle must also contribute.

Additionally, it pulls the Angulus inferior scapulae to the side when lifting the arm. This regulates the position of the arm against the scapula and shortens the angle between the scapula and the arm.