There are major pectoral muscles and minor pectoral muscles. The major ones are across the upper part of the chest, adducting, flexing, and rotating the arms medially. They originate in the clavicle, the sternum, the six upper ribs, and the aponeurosis of the obliquus externus abdominis. These origins are reflected in the subdivision of the muscle into clavicular, sternocostal, and abdominal parts. Their insertion is into the crest of the intertubercular groove of the humerus. Innervation is through the anterior thoracic. The minor pectoral muscles lie under the major pectoral muscles, drawing the shoulder downward. They originate in the third, fourth, and fifth ribs and insert into the coracoid process of the scapula, receiving innervation from the anterior thoracic.

The muscles in your chest which allow you to push your arms forward.

muscles attached to the front of the chest wall and upper arms. The larger one is called pectoralis major, and the smaller one is called pectoralis minor. Because these muscles are next to the breast, breast cancer may spread to them, althought this happens rarely.