Pectoralis Major Muscle
The pectoralis major muscle is a strong, fan-shaped muscle of the shoulder joint. It makes up the bulk of the chest muscles in the male and lies under the breast in the female. Underneath the pectoralis major is the pectoralis minor, a thin, triangular muscle. The pectoralis major muscle lowers the arm back toward the body when the arm is extended overhead, moves the arm in toward the body, and moves arm in and across the front of the body.