The pectoralis major arises from parts of the clavicle and sternum, costal cartilages of the true ribs, and the aponeurosis of the abdominal external oblique muscle; it inserts onto the lateral lip of the bicipital groove.

It arises from the anterior surface of the sternal half of the clavicle from breadth of the half of the anterior surface of the sternum, as low down as the attachment of the cartilage of the sixth or seventh rib; from the cartilages of all the true ribs, with the exception, frequently, of the first or seventh, and from the aponeurosis of the abdominal external oblique muscle.

[2][3] From this extensive origin the fibers converge toward their insertion; those arising from the clavicle pass obliquely downward and outwards (laterally), and are usually separated from the rest by a slight interval; those from the lower part of the sternum, and the cartilages of the lower true ribs, run upward and laterally, while the middle fibers pass horizontally.

They all end in a flat tendon, about 5 cm in breadth, which is inserted into the lateral lip of the bicipital groove (intertubercular sulcus) of the humerus.

The sensory feedback from the pectoralis major follows the reverse path, returning via first-order neurons to the spinal nerves at C5, C6, C8, and T1 through the posterior rami.

[4] After the synapse in the posterior horn of the spinal cord, sensory information concerning movement of the muscle, proprioception, and pressure then travels through a second-order neuron in the dorsal column medial lemniscus tract to the medulla.

[citation needed] Poland syndrome is a rare congenital condition in which the whole muscle is missing, most commonly on one side of the body.

This type of injury is known to affect the athletic population, namely in high-impact contact sports such as powerlifting, and may result in pain, weakness, and disability.

In developed countries, most lesions occur in male athletes, especially those practicing contact sports and weight-lifting (particularly during a bench press maneuver).

[13] The injury is characterized by sudden and acute pain in the chest wall and shoulder area, bruising and loss of strength of the muscle.

High grade partial or full thickness tears warrant surgical repair as the preferred treatment if function is to be preserved, particularly in the athletic population.

Poland syndrome is a congenital anomaly in which there is a malformation of the chest causing the pectoralis major on one side of the body to be absent.

Other characteristics of this disease are "unilateral shortening of the index, long, and ring fingers, syndactyly of the affected digits, hypoplasia of the hand, and the absence of the sternocostal portion of the ipsilateral pectoralis major muscle".

The latissimus dorsi and teres major also aid in adduction and medial rotation of the arm, so they may be able to compensate for the lack of extra muscle.

The treatment in these cases involves complete surgical excision because of the risk of liposarcoma they post especially large intramuscular liposomas.