What are the two heads of the pectoralis major and their origins?

• A. Clavicular head from medial half of clavicle; sternocostal head from sternum and upper costal cartilages.
• B. Clavicular head from scapula; sternocostal head from sternum and lower costal cartilages.
• C. Both heads originate from sternum.
• D. Clavicular head from acromion; sternocostal head from ribs 7-9.

Answer: (A)

The pectoralis major has two heads: a clavicular head and a sternocostal head. The clavicular head originates from the medial half of the anterior surface of the clavicle, while the sternocostal head originates from the sternum and the upper costal cartilages (upper ribs). They converge to insert on the lateral lip of the intertubercular groove of the humerus. This arrangement explains why the clavicular portion helps flex the arm, whereas the sternocostal portion powers adduction and medial rotation, with strong contribution when the arm is extended from a flexed position.