In the anatomy of mammals, a nipple or mammary papilla or nipple is a small projection of skin containing the outlets for 15-20 lactiferous ducts arranged around the cylindrical tip. The skin of the nipple is a rich supply of special nerves that are sensitive to certain stimuli. The physiological purpose of nipples is to deliver milk to the infant, 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. Newborn mammals have a rooting instinct (moving their heads to include their mouths to anything touching their face) to request the nipple, and a sucking instinct for extracting milk. Mammals typically have an even number of nipples arranged bilaterally around. They develop in the embryo, along the lines "milk."
Most mammals develop multiple nipples along each line of milk, with the total approximate size of the maximum capacity, and half of the total (ie the number one side) approximating the size range average for this species. In primitive mammals - the monotremes like the platypus - mammary glands empty onto the skin without a nipple. In cetaceans such as whales, the child can not form a vacuum seal to a nurse, because of its structure mouth nipple whale is unlike that of any other mammal. Rather than requiring action by the suction, discharge of milk is supplied by muscles tongue. The calf has extended the nipple in his mouth, and the mother ejects or expels her milk into the mouth of the calf. The pigments of the nipple and areola are Brown eumelanin, a brown pigment, and pheomelanin a greater extent, a red pigment. In many women, there are small bumps on the areola, which are called 'Montgomery bodies. In humans, the nipple is innervated by the fourth intercostal nerve.
