Pectoralis major is a large muscle which covers the upper chest anteriorly and contributes to the anterior axillary fold. The pectoralis major arises from the side of the sternum, the shaft of the clavicle, and cartilages of the first 7 ribs, with fibers converging to attach to the lateral lip of the bicipital groove of the humerus. Pectoralis major is primarily a glenohumeral medial rotator and adductor, although it is also important in initiating glenohumeral flexion via its clavicular portion.

Pectoralis minor lies immediately deep to pectoralis major. The pectoralis minor courses from the 3rd, 4th, and 5th ribs to the coracoid process of the scapula. The primary function of the pectoralis minor is stabilization of the shoulder girdle; crutch walkers may use the pectoralis minor as they lift the trunk against a stationary shoulder girdle base during ambulation. The pectoralis minor also assists the lower trapezius.

Subclavius is a small muscle which may be observed connecting the first rib and clavicle. Its primary function is stabilization of the clavicle, and hence the shoulder girdle. The subclavius also depresses and protracts the clavicle.

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