Anatomy · Muscles

Pectoralis major

The large fan-shaped muscle of the upper chest

Chest · anterior wall, moves the arm

A thick, fan-shaped muscle that covers the upper front of the chest and lies over the breast. Its fibres converge from the collarbone, breastbone and upper ribs on a flat tendon on the humerus, and it draws the raised arm across the body and rotates it inwards. It forms the front wall of the armpit.

How to spot them

▸A fan of fibres from the collarbone, sternum and upper costal cartilages converging on the upper arm
▸Two heads, clavicular above and sternocostal below, whose flat tendon twists before it attaches to the humerus
▸Its lower border makes the anterior axillary fold, the visible ridge at the front of the armpit
▸Supplied by the lateral and medial pectoral nerves

What to know

The large fan-shaped muscle of the upper chest whose two heads converge on the lip of the bicipital groove of the humerus

Pectoralis major — clavicular and sternocostal heads.

It forms the ridge of skin at the front of the armpit, and its tendon twists before it attaches to the humerus

Pectoralis major — the anterior axillary fold.

Two nerves named for the cords of the brachial plexus they come from supply it, the lateral one piercing the fascia below the collarbone

Pectoralis major — the lateral and medial pectoral nerves.

Failure of one side to develop, with a missing breast bud and short webbed fingers, is a recognised congenital pattern

Pectoralis major — Poland syndrome, absence of the sternocostal head.

Ruptures of its tendon are classically seen in weightlifters during the bench press

Pectoralis major — the chest press loads its tendon at the humerus.

It brings the raised arm across the chest and rotates it inwards; the upper fibres also lift the arm forwards

Pectoralis major — adduction and medial rotation, with flexion by the clavicular head.

A large flap of this muscle, with its skin, was long used to rebuild defects of the head and neck and the chest wall

Pectoralis major flap — a workhorse of reconstructive surgery.

Key ideas

Because its attachment is at the front of the humerus, it is the strongest muscle pulling the arm forwards and inwards, as in a push-up or a throw; the clavicular head acts best with the arm above shoulder height.
Its flat tendon is folded on itself: the fibres from the lower part of the muscle pass behind those from the upper part before they attach, so the two heads pull on different parts of the groove.

Quick-fire facts

•Origin: clavicular head from the medial half of the clavicle; sternocostal head from the sternum, the upper six costal cartilages and the aponeurosis of the external oblique
•Insertion: the lateral lip of the intertubercular (bicipital) groove of the humerus
•Action: adducts and medially rotates the arm; the clavicular head also flexes it, and the sternocostal head extends it from a flexed position
•Nerve supply: lateral pectoral nerve (C5 to C7) and medial pectoral nerve (C8, T1)
•Blood supply: pectoral branch of the thoracoacromial artery and branches of the internal thoracic artery
•Forms the anterior wall of the axilla, with the pectoral (anterior axillary) fold as its lower border
•The deltopectoral groove between it and the deltoid contains the cephalic vein
•It lies over pectoralis minor and the ribs; the breast rests on its fascia
•Poland syndrome, absence of the sternocostal head, is usually unilateral and often affects the hand on the same side

Drill it — 7 cards

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Sources

TeachMeAnatomy — Pectoralis major
TeachMeAnatomy — Muscles of the pectoral region