Do you want the secret to developing a defined, enviable chest? It's the underrated, but extremely essential, pectoralis minor muscle. This muscle is thin and flat; it lies underneath the larger pectoralis major, which consequently gets all the fanfare.
The pectoralis minor is a thin, flat muscle found immediately underneath the pectoralis major. This is the smaller of the two pectoral muscles, or muscles of the chest. This muscle extends from three origins on the third, fourth, and fifth ribs on each side of the ribcage to the coracoid process (a small, hook-like structure) of the scapula, or shoulder blade. The origins of the muscle are all lateral to the costal cartilages. The primary actions of this muscle include the stabilization, depression, abduction or protraction, upward tilt, and downward rotation of the scapula. When the ribs are immobilized, this muscle brings the scapula forward, and when the scapula is fixed, it lifts up the rib cage. There are two parallel pectoralis minor muscles, one on each side of the sternum. Both pectoralis muscles work with the serratus anterior muscles to create a full range of movement for the scapula. The pectoralis minor muscle receives its arterial supply from the thoracoacromial trunk's pectoral branch. Innervation or stimulation comes from the clavicular head at C8 and T1 and the medial pectoral nerves.