The |teres major| is a short and thick, somewhat flattened muscle that extends from the |scapula| (shoulder blade) to the |humerus| (upper arm bone). This muscle creates part of the ~posterior~ wall of the armpit and helps adduct the arm. It also rotates the arm medially behind the back. The |teres major| tenses when the arm lies next to the body. When the arm is extended the |teres major| is stretched, becoming elongated and thinner.
