PECTORALIS MAJOR
Large fan-shaped, superficial muscle covering the upper portion of the chest. Its origins are the clavicle, sternum, cartilage of first six ribs and the aponeurosis of the external oblique muscles. It inserts on the greater tubercle of the humerus. This is the prime mover of flexion of the arm. It also adducts and medially rotates the arm. During exercise, it assists in forced inspiration.