Kinds of Nipple
A nipple or mammary papilla is a small projection of skin containing the outlets for 15-20 lactiferous ducts arranged cylindrically around the tip. The physiological purpose of nipples is to deliver to the infant milk produced in the female mammary glands during lactation. In the male, nipples are often not considered functional with regard to breastfeeding, although male lactation is possible. Mammalian infants have a rooting instinct for seeking the nipple, and a sucking instinct for extracting milk.