<Tr> <Td_colspan="2"> Anatomical terminology (edit on Wikidata) </Td> </Tr> <P> A mammary gland is an exocrine gland in mammals that produces milk to feed young offspring . Mammals get their name from the Latin word mamma, "breast". The mammary glands are arranged in organs such as the breasts in primates (for example, humans and chimpanzees), the udder in ruminants (for example, cows, goats, and deer), and the dugs of other animals (for example, dogs and cats). Lactorrhea, the occasional production of milk by the glands, can occur in any mammal, but in most mammals, lactation, the production of enough milk for nursing, occurs only in phenotypic females who have gestated in recent months or years . It is directed by hormonal guidance from sex steroids . In a few mammalian species, male lactation can occur . </P> <P> The basic components of a mature mammary gland are the alveoli (hollow cavities, a few millimeters large) lined with milk - secreting cuboidal cells and surrounded by myoepithelial cells . These alveoli join to form groups known as lobules . Each lobule has a lactiferous duct that drains into openings in the nipple . The myoepithelial cells contract under the stimulation of oxytocin, excreting the milk secreted by alveolar units into the lobule lumen toward the nipple . As the infant begins to suck, the oxytocin - mediated "let down reflex" ensues and the mother's milk is secreted--not sucked from the gland--into the baby's mouth . </P> <P> All the milk - secreting tissue leading to a single lactiferous duct is called a "simple mammary gland"; in a "complex mammary gland" all the simple mammary glands serve one nipple . Humans normally have two complex mammary glands, one in each breast, and each complex mammary gland consists of 10--20 simple glands . The presence of more than two nipples is known as polythelia and the presence of more than two complex mammary glands as polymastia . </P>

What part of the mammary gland produces milk