Pectoralis major

Clavicular head:

-anterior surface of the medial half of the clavicle.

Sternocostal head:
-anterior surface of the sternum, the superior six costal cartilages, and the aponeurosis of the external oblique muscle

Intertubercular groove of the humerus

Clavicular head:

-flexes the humerus

Sternocostal head:
-extends the humerus as a whole, adducts and medially rotates the humerus. It also draws the scapula anteriorly and inferiorly.

Lateral pectoral nerve and medial pectoral nerve

Clavicular head: C5 and C6

Sternocostal head: C7, C8 and T1

Pectoral branch of the thoracoacromial trunk

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Variations:

The more frequent variations include greater or less extent of attachment to the ribs and sternum, varying size of the abdominal part or its absence, greater or less extent of separation of sternocostal and clavicular parts, fusion of clavicular part with deltoid, and decussation in front of the sternum.

Deficiency or absence of the sternocostal part is not uncommon.

Absence of the clavicular part is less frequent.

Rarely, the whole muscle is missing. This may accompany absence of the breast in females.

Training:

The pectoralis muscle can be trained for athletic or bodybuilding purposes. The following compound exercises are often used to increase the strength and mass of the muscle:

Bench press, with various bench angles (flat, incline, and decline)
Push up
Dips

Isolation exercises include:

Flyes or Flies
Cable Crossovers
“Pec Deck” machines