Pectoralis major muscle (Musculus pectoralis major) is a broad, fan-shaped muscle on the front of the chest. It lies beneath the skin and breast, extends from the collarbone and central chest to the upper arm, and moves the arm at the shoulder while forming the front fold of the armpit.
Where is the pectoralis major muscle located?
The muscle covers much of the upper anterior chest wall, meaning the front of the chest. Its superficial surface, the surface nearer the skin, is covered by pectoral fascia, a sheet of connective tissue. The breast lies in the fatty connective tissue superficial to this fascia.
Its deep surface faces the ribs, the muscles between them, and pectoralis minor, a smaller chest muscle beneath it. Towards the shoulder, pectoralis major lies beside the deltoid, the muscle covering the shoulder. A groove between these muscles carries the cephalic vein, a vessel that returns blood from the upper limb.
The lower free border forms the anterior axillary fold: the raised muscular edge at the front of the axilla, or armpit. This fold is a useful surface landmark distinguishing the chest muscle from the deeper contents of the armpit.
What are the parts of the pectoralis major muscle?
A muscle head is a portion distinguished by its attachment at one end. The clavicular head of pectoralis major muscle forms the upper portion, while the sternocostal head of pectoralis major muscle forms the larger portion below it.
The heads have different fibre directions but converge towards the upper arm. Upper fibres pass mainly outwards and downwards; lower fibres pass outwards and upwards. Their arrangement helps explain why the heads contribute differently to shoulder movement.
| Part | Attachment or arrangement | Functional significance |
|---|---|---|
| Clavicular head | Begins on the front of the medial clavicle | Helps move the arm forwards |
| Sternocostal head | Begins on the sternum, upper costal cartilages and adjacent connective tissue | Helps draw the arm inwards and return a raised arm backwards |
| Shared tendon | Converges on the upper humerus | Transfers the pull of both heads to the arm |
A tendon is the strong connective tissue through which a muscle transmits force to its attachment. The broad muscle belly narrows into this tendon near the upper arm.
Where does the pectoralis major muscle originate and insert?
The origin is the attachment conventionally described as the muscle's starting point; the insertion is its attachment at the other end. These terms do not mean that the origin must remain fixed during every movement.
The main origins are:
- The anterior surface of the medial part of the clavicle, or collarbone; medial means nearer the body's midline.
- The anterior surface of the sternum, or breastbone.
- The upper costal cartilage, the flexible tissue connecting the upper ribs to the sternum.
- The rectus sheath, the connective tissue covering around rectus abdominis, the long muscle on the front of the abdomen.
The insertion is on the lateral lip of the intertubercular sulcus of the humerus. The humerus is the upper-arm bone; its intertubercular sulcus is a groove between two bony prominences near the shoulder. The lateral lip is the edge farther from the body's midline, not the floor of the groove.
What movements does the pectoralis major muscle produce?
The muscle acts at the shoulder joint, where the head of the humerus meets the shoulder blade. Its main shared actions are adduction, drawing the arm towards the body, and medial rotation, turning the upper arm inwards.
The clavicular head assists flexion of the arm at the shoulder joint, meaning movement forwards. The sternocostal head can produce extension of the arm via the shoulder joint when the arm is already flexed, bringing a forward-raised arm back towards the body. It should not be understood as simply pulling the resting arm backwards in every position.
Together, the heads also bring an outstretched arm across the front of the chest. If the upper limbs are fixed, the muscle can instead help move the trunk towards them, illustrating how movement depends on which attachment is held steady.
Which nerves supply the pectoralis major muscle?
The medial pectoral nerve and lateral pectoral nerve provide its innervation, meaning its nerve supply. Both arise from the brachial plexus, the network of nerves supplying the upper limb.
The lateral pectoral nerve supplies the upper part prominently, while the medial pectoral nerve contributes especially to the lower part. Their territories overlap rather than forming a sharp boundary between the heads. The nerves approach the muscle from its deep surface.
What is its blood supply and venous drainage?
The pectoral branch of the thoraco-acromial artery is an important source of arterial blood, which reaches tissues through arteries. The lateral thoracic artery also contributes to the supply.
Venous drainage is the return of blood through veins. Blood leaves through accompanying pectoral veins and the lateral thoracic vein, ultimately reaching the axillary vein in the armpit.
How can I locate it in the 3D model?
In the 3D model next to the article, rotate to an anterior view, select the pectoralis major muscle and isolate it. Zoom in and rotate towards a lateral view, then hide selected structures or pull parts apart to change the view; cut a section along the sagittal, coronal or transverse plane for another viewing option. Fade the muscle or switch layers on and off to explore its relationships with neighbouring structures.