Breast

The human breasts are paired organs lying on the anterior chest, extending from the second to the sixth ribs. The breasts in other animals are usually multiple and extend on to the abdomen, which explains the rare anomaly of multiple paired breasts that occasionally occurs in humans. The breasts are thought to be modified sweat glands, and therefore lie in the subcutaneous fat in front of the pectoral (chest) muscles. The breast has a central nipple through which the fifteen to twenty milk ducts exit; the nipple is usually protuberant, but can be inverted in some women.

The breast develops in young girls at around the age of ten or eleven due to the increasing release of pituitary hormones in puberty. The gland grows into the normal conical or rounded adult shape by around sixteen years of age, but swells considerably in pregnancy when milk production occurs. During the normal menstrual cycle, many women experience breast tenderness and swelling during the seven to ten days prior to menstruation.