Clavicular head of pectoralis major muscle

At a glance

English

Clavicular head of pectoralis major muscle

Latin (TA2)

Pars clavicularis musculi pectoralis majoris

System

Muscle

Region

Trunk

Side

Paired, left and right

About the clavicular head of pectoralis major muscle

Pectoralis major is the large fan of muscle that shapes the front of the chest, and its upper border is formed by a separate band of fibres from the collarbone: the clavicular head. A narrow cleft usually divides this band from the much larger sternocostal head below it, so the two can be seen and tested as distinct parts in a lean, muscular person.

The fibres begin on the front of the medial half of the clavicle and slope downward and outward over the shoulder joint. Laterally they gather into the front layer of the flat, two-layered tendon that attaches to the lateral lip of the intertubercular sulcus of the humerus. Their attachment is placed lowest on that lip, so the tendon looks twisted as the deeper sternal fibres pass up behind them. Along its outer edge the head lies against the anterior fibres of deltoid; the small gap between them, the deltopectoral groove, carries the cephalic vein towards the axillary vein.

Because its line of pull passes in front of the shoulder and upward, this head behaves differently from the rest of the muscle. It raises the arm forwards (flexion), draws it across the chest in horizontal adduction and turns the humerus inwards. The lower, sternocostal fibres instead pull the raised arm down and back, so the two heads partly oppose each other. The clavicular head is supplied mainly by the lateral pectoral nerve, carrying fibres from the fifth and sixth cervical segments, which reaches the deep surface of the muscle.

Clinically, pectoralis major is tested by asking the patient to press the hands together or to push the raised arm forward against resistance; the clavicular head stands out during resisted flexion. Tears of the whole muscle are uncommon and usually happen at the junction of muscle and tendon during heavy bench pressing; a sudden pain, bruising over the arm and loss of the front fold of the armpit follow. In Poland syndrome part or all of the muscle fails to develop on one side, though the clavicular part is spared more often than the sternocostal part.

Attachments, action and supply

Origin

Anterior surface of the medial (sternal) half of the clavicle.

Insertion

Lateral lip of the intertubercular sulcus of the humerus, via the anterior lamina of the pectoralis major tendon.

Action

Flexes the arm at the shoulder, adducts it horizontally across the chest and rotates the humerus medially.

Nerve supply

Lateral pectoral nerve (C5, C6), with some fibres from the medial pectoral nerve.

Blood supply

Pectoral and deltoid branches of the thoracoacromial artery.