The fan-shaped Pectoralis Majors are the largest muscles in the upper chest. Connecting at the breastbone, these superficial (close to the skin) muscles span on both sides of the chest from the armpit to the collarbone and down over the lower chest area. The pair, generally referred to as the ‘pecs’, make up the bulk of the chest musculature. Hidden in females beneath the breasts, the Pectoralis Majors are particularly prevalent in well-developed males.
Although a major function is keeping the arms attached to the body, the pectorals are primarily tasked at controlling them, capable of moving each shoulder joint in four different directions. The Pectoralis Major also assists with heavy breathing, providing space for lung expansion by pulling the ribcage back.