The |subscapularis| is a large triangular shoulder muscle that lies on the front surface of the |scapula| (shoulder blade) in the concave area called the subscapular |fossa|. The muscle converges at its lower end into a ~tendon~ which inserts in the |humerus| (upper arm bone). This muscle rotates the head of the |humerus| when the arms are raised tp prevent displacement. It is also used to move the arms forward and down.