The pectoralis major (PM) is an intricate anatomic structure. The muscle is divided anatomically into a clavicular and sternal head. Notably, some authors describe a small, third abdominal head arising from the aponeurosis of the external oblique muscle or from the fifth through seventh costal cartilages. The clavicular head is composed of a single muscle segment, whereas the sternal head is composed of 6-7 separate muscle segments. The sternal head constitutes approximately 80% of the PM muscle.