Pectoralis major muscle

The pectoralis major muscle is a muscle of the pectoral region, overlying the anterior chest wall but is considered an upper limb muscle due to its function. 

Pectoralis major is a large, fan-shaped muscle. It covers much of the front upper chest. It is composed of two parts:

  • sternal part beginning at the sternum and the first six costal cartilages
  • clavicular part takes origin from the clavicle

The heads of the pectoralis major converges on the humerus where it inserts into the bicipital groove.

  • the thoracoacromial artery provides its major blood supply
  • the intercostal perforators arising from the internal mammary artery provide a segmental blood supply. 
  • the blood supply that provides circulation to this muscle perforates through to the breast, thus also providing its blood supply

The medial and lateral pectoral (or anterior thoracic) nerves provide innervation for the muscle, entering posteriorly and laterally.

The function of this muscle is to bring the humerus across the chest, allowing to flex, adduct, and rotate the arm medially.

The breast lies over the musculature that encases the chest wall. These muscles involved include pectoralis majorserratus anteriorexternal oblique, and rectus abdominis fascia. By maintaining continuity with the underlying musculature, the breast tissue remains richly perfused.

Depending on a woman's habitus, pectoral muscles have variable angles of obliquity:

  • short, stocky women have more horizontally oriented pectoral muscles
  • tall, thin women have them more vertically oriented

This element is very important for proper positioning in the efficacy of the medial lateral oblique (MLO) view in mammography: the compression of a pectoralis major differently oriented over a breast support inclined at 45° will produce a deformed geometric projection of the muscle and abnormal distribution of the quadrants, masking the "milky way" partially.

On adequate mammogram it is recommended that pectoralis major is seen through to the level of the nipple.

Anatomy: Upper limb
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Article information

rID: 15425
Section: Anatomy
Synonyms or Alternate Spellings:
  • Pec major muscle
  • Pectoralis major muscles

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Cases and figures

  • Figure 1: anterior arm anatomy
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  • Normal MLO and CC...
    Case 1: normal appearance on mammography
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