Sternocostal head of pectoralis major muscle

At a glance

English

Sternocostal head of pectoralis major muscle

Latin (TA2)

Pars sternocostalis musculi pectoralis majoris

System

Muscle

Region

Trunk

Side

Paired, left and right

Inserts on

The body of sternum and manubrium of sternum

About the sternocostal head of pectoralis major muscle

Pectoralis major is the fan-shaped muscle that gives the chest its shape, and most of its bulk belongs to the sternocostal head. This part lies below the smaller clavicular head, from which it is usually separated by a slight cleft, and its lower edge forms the rounded front fold of the armpit. Some fibres from the external oblique aponeurosis at its lower edge are often described as a separate abdominal part.

Its origin is long and curved. It arises from the front of the manubrium and body of the sternum, from the cartilages of the upper six ribs and from the external oblique aponeurosis. From this wide base the fibres converge on the humerus: the upper ones run nearly horizontally, the lower ones climb steeply upward and outward. They attach to the lateral lip of the intertubercular sulcus through the deep, posterior layer of the muscle's flat tendon. Because the lowest fibres attach highest on the humerus, passing behind the upper ones, the tendon appears twisted, an arrangement that keeps the fibres at an even tension when the arm is raised.

Working with the clavicular head, the sternocostal head adducts the arm and turns it inwards. Its distinctive action is to pull the arm down and forward from a raised position, the movement used in climbing, chopping or a swimming stroke. It can also extend the flexed arm back towards the side of the body, though not beyond it. It is supplied by both pectoral nerves, chiefly the medial pectoral nerve carrying fibres from the seventh cervical to first thoracic segments. Blood comes from the pectoral branch of the thoracoacromial artery, perforating branches of the internal thoracic artery and the lateral thoracic artery.

Rupture of pectoralis major most often involves this head and happens at the tendon during heavy bench pressing, causing pain, bruising and loss of the armpit fold; complete tears are usually repaired surgically. In Poland syndrome the sternocostal part is the portion most often missing, giving an asymmetric chest.

Attachments, action and supply

Origin

Anterior surface of the manubrium and body of the sternum, cartilages of the upper six ribs and the aponeurosis of the external oblique.

Insertion

Lateral lip of the intertubercular sulcus of the humerus, via the deep layer of the tendon.

Action

Adducts and medially rotates the arm; draws the raised arm downward and forward and extends the flexed arm to the side.

Nerve supply

Medial and lateral pectoral nerves (mainly C7, C8, T1).

Blood supply

Pectoral branch of the thoracoacromial artery, perforating branches of the internal thoracic artery and the lateral thoracic artery.