innerbody
Diagram

Teres Major Muscle

The teres major muscle is a thick, flattened muscle that brings the arm toward the body and assists in extending it when the arm is in a flexed position. There are two teres muscles. The other one is the teres minor muscle, which rotates the arm laterally and assists in bringing it toward the body. As it draws the upper arm bone (humerus) up, it strengthens the shoulder joint. The teres major muscle Continue Scrolling To Read More Below...

Continued From Above... also aids in rotating the arm but its function is just the opposite of the teres minor and other muscles in the rotator cuff.