The pectoralis major muscle is a large muscle of the chest that pulls the arm in toward the body when contracted. There is one pectoralis major on each side of the chest.
The pectoralis major originates at the clavicle, sternum, and several ribs covering most of the center of the chest.
The insertion is at two points on the top of the humerus.
The pectoralis major is innervated by the medial pectoral nerve and the lateral pectoral nerve.
The pectoralis major muscles, often called 'pecs' in the bodybuilding world, are developed mainly with the bench press.
The word pectoralis major comes from pectoralis, Latin for of the chest or of the breast. The major part of the word differentiates it from the pectoralis minor muscle, which sits underneath.