The Pectoralis major is a muscle of the pectoral region. This muscle along with the Pectoralis minor, Subclavius and Serratus anterior forms the pectoral region. It is the largest muscle in this region. Morphologically it is thin and fan-shaped. It is characterized by 2 heads, the large Sternocostal head, and the small Clavicular head. ORIGIN The Sternocostal head arises from- Medial parts of 2nd-6th costal cartilages and aponeurosis of the external oblique muscle of the abdomen. Lateral half of the anterior surface of the sternum up to 6th costal cartilage. The Clavicular head arises from the medial half of the anterior aspect of the clavicle. INSERTION Pectoralis major is inserted by a bilaminar tendon on the lateral lip of the bicipital groove of the humerus. This tendon has an anterior lamina and a posterior lamina. Anterior lamina is thick, short and is formed by clavicular fibers. Posterior lamina is thin, long and is formed by sternocostal and aponeurotic fi...