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Pectoralis major

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Pectoralis Major

The pectoralis major is the largest and most superficial muscle of the anterior chest wall. It directly underlies the breast, separated from it by deep fascia and loose connective tissue of the retromammary space.

Origin (3 Parts)

Part	Origin
Clavicular head	Medial half of the clavicle
Sternocostal head	Sternum + costal cartilages of ribs 1-7; anterior surface of sternum
Abdominal part	Anterior layer of the rectus sheath / aponeurosis of external oblique

Insertion

Lateral lip of the intertubercular sulcus (bicipital groove) of the humerus
The tendon twists on itself: fibers with a superior origin insert lower/more anteriorly; fibers with an inferior origin insert higher

Actions

Action	Part Responsible
Adduction of arm	Entire muscle
Medial (internal) rotation of arm	Entire muscle
Flexion of arm	Clavicular + sternocostal parts
Flexion from extended position	Clavicular head primarily
Extension from flexed position (against resistance)	Sternocostal head
Assists respiration	When shoulder girdle is fixed

Innervation

Medial pectoral nerve (C8-T1) - mainly to the sternocostal head
Lateral pectoral nerve (C5-C7) - mainly to the clavicular head
Together they cover the full nerve root range of C5-T1

Blood Supply

Thoraco-acromial artery (pectoral branch) - primary supply
Lateral thoracic artery - supplementary

Diagrams

Anterior view - pectoralis major and the pectoral region:

Pectoralis major and pectoral region muscles, nerves, and arteries

Lateral view - the two heads of pectoralis major:

Pectoralis major clavicular head and sternocostal part with rib levels

Key Clinical Points

Its inferior margin forms the anterior axillary fold
A rupture of pectoralis major is a sports injury, most common in weightlifters during bench press; the sternocostal head tears most often at the musculotendinous junction or humeral insertion
The muscle is used as a pedicled flap (pectoralis major myocutaneous flap) in reconstructive head and neck surgery, supplied by the pectoral branch of the thoraco-acromial artery
In pectoralis major transfer procedures (e.g., for irreparable subscapularis tears), the sternal head is detached and transferred to restore internal rotation

Sources: Gray's Anatomy for Students; THIEME Atlas of Anatomy - General Anatomy and Musculoskeletal System; Miller's Review of Orthopaedics 9th Ed; Campbell's Operative Orthopaedics 15th Ed

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