Pectoralis Major

The Pectoralis major, or pectoral muscle, is a fan-shaped muscle, located at the upper front of the chest wall. It constitutes the bulk of the chest muscles in the male and lies under the breast in the female. The Pectoralis major is innervated by the lateral pectoral nerve and the medial pectoral nerve, pulling the arm across the chest, rotating it inwards as it contracts.

The Pectoralis major is divided into two heads: 1) the clavicular head originates at anterior surface of the medial half of the clavicle; 2) the sternocostal head arises from anterior surface of the sternum, the superior six costal cartilages, and the aponeurosis of the external oblique muscle. The pectoral muscle is inserted in the intertubercular groove of the humerus (upper arm bone).