Final answer:
About 1/3 of the breast rests on the serratus anterior muscle, which aids in the stabilization and movement of the scapula, unlike the pectoralis minor which positions the pectoral girdle.
Step-by-step explanation:
The greater part of the breast, about 2/3, rests on the pectoralis major muscle; and the rest, about 1/3, on the serratus anterior muscle.
The pectoralis minor is one of the muscles that position the pectoral girdle, but it does not primarily support the breast tissue.
Other muscles that stabilize the pectoral girdle are the subclavius, trapezius, levator scapulae, rhomboid major, and rhomboid minor.
The pectoralis major is a thick, fan-shaped muscle that covers much of the superior thorax, while the serratus anterior is a muscle that lies on the side of the thorax and plays a role in the movement and stabilization of the scapula.