A mammary gland is an organ in female mammals that produces milk to feed young offspring.Mammals get their name from the word mammary.. In humans, the mammary glands are situated in the breasts. In ruminants such as cows, goats, and deer, the mammary glands are contained in the udders.The mammary glands of mammals other than primates, such as dogs and cats, are sometimes called dugs.fter delivery, lactation occurs within the mammary gland; lactation involves the secretion of milk by the luminal cells in the alveoli. Contraction of the myoepithelial cells surrounding the alveoli will cause the milk to be ejected through the ducts and into the nipple for the suckling pups.