The human breast moves in complex ways, a fleshy oscillation. This was demonstrated in an experiment conducted by Australian researchers, in which large-busted women ran on a treadmill while wearing infrared-emitting diodes on their chests. I wince at the thought of it. Breasts have no muscle; they are collections of glandular and fibrous connective tissues and fat, supported in part by the skin. The average weight of a woman’s breast is around a pound, but breast weights of ten pounds and above are possible; breasts range from soft lemons to flopping eggplants, and they swing, brother: a demonstration of Newton’s second law with every step.
Unlike other mammals, humans have breasts that remain mature outside lactation. We are born with mammary glands spread within the chest wall, stretching from the armpit down toward the groin, but not with breasts. They are the only organs to develop after birth — usually a single pair, though extra breasts do occur, in both men and women. Unmistakable, yet greatly varied, the visible breast can be shaped like a pear, melon, apricot, or orange — for some reason, produce is a common metaphor — but also like a cone, sausage, softball, plate, ham, or loaf of bread. The fibrous tissue of the breast is a kind of suspensory structure called Cooper’s ligaments that allows the breasts to move freely but gives little support. Breasts may lie near each other or be widely spaced; they may grow high on the chest or low. The nipples can point toward each other, away from each other, up, down, or straight ahead.