What separates the breast from the pectoral muscle?

The retromammary space is the area that separates the breast tissue from the underlying pectoral muscle. This potential space contains connective tissue and enables the breast to move slightly during various physical activities, contributing to its mobility. The presence of this space is significant because it allows for the natural movement of the breast without compromising its attachment to the muscles beneath.

Cooper's ligaments provide support to the breast by anchoring it to the overlying skin and surrounding structures, but they do not specifically separate the breast from the pectoral muscle. Adipose tissue, while it plays a critical role in the overall composition of the breast and supports its structure, does not function as a barrier between the breast and the muscle. Lactiferous ducts are involved in transporting milk but do not have a role in separating breast tissue from the underlying muscle. Thus, the retromammary space is the correct choice as it specifically refers to the anatomical relationship between the breast and the pectoral muscle.