The breast muscle.

This muscle arises from one of the bones of the shoulder-girdle and passes to the limb. Its fleshy fibers converge as they pass outwards to this limb. The highest fibers pass downwards and outwards in front of the lowest fibers which pass upwards and outwards. Between the two extremes they have varying degrees of obliquity.

The pectoralis major draws down the uplifted arm. It may also draw forward the limb. The lower fibres of the muscle assist in depressing the shoulder while the upper fibers,which spring from the collar-bone, help to bend the arm forwards at the shoulder-joint.

The breast or mammary gland is situated in the fat which overlies the muscle.