Lower border of teres major muscle

The lower border of teres major muscle constitutes an important anatomical landmark on the posterior aspect of the shoulder. Together with the latissimus dorsi, it forms the inferior limit of the posterior wall of the axilla, thereby delineating the transition between the axillary and brachial regions. This border serves as a key reference point for identifying the continuation of the axillary artery as the brachial artery. Correspondingly, the axillary vein begins at this same level, as a continuation of the basilic and brachial veins.

In addition the lower border of teres major muscle defines the superior boundary of the triangular interval, an important gateway through which the radial nerve and profunda brachii artery pass from the axilla into the posterior compartment of the arm.