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Etymology: L, pectus, breast
a large muscle of the upper chest wall that acts on the joint of the shoulder. Thick and fan-shaped, it arises from the clavicle, the sternum, the cartilages of the second to the sixth ribs, and the aponeurosis of the obliquus externus abdominis. It serves to flex, adduct, and medially rotate the arm in the shoulder joint.
A large triangular muscle that extends from the sternum to the humerus and functions to flex, horizontally adduct, and internally rotate the arm, and aids in chest expansion when the upper extremities are stabilized.
See also: pectoralis