Large, fan-shaped muscle covering the upper part of the chest and forming the anterior axillary fold (front part of the armpit). The pectoralis has two origins: the clavicular pectoralis major originates from the median half of the clavicle, and the sternal pectoralis major originates from the anterior sternum and the cartilage of the first six ribs. The fibres of the muscle converge to insert onto the lateral aspect of the humerus, just below its head. The primary actions of the clavicular pectoralis major are flexion and horizontal adduction about the shoulder; those of the sternal pectoralis major are extension. adduction, and horizontal adduction. The pectoralis major plays an important role in climbing and throwing. When the scapula and arm are fixed, the pectoralis major pulls the ribcage upwards, contributing to inspiratory movements.
Subjects: Sports and Exercise Medicine.