Mammary glands are used by females to produce milk for nourishment of her young. They are considered to be exocrine glands and enlarged versions of sweat glands. They are also found in males but are inactive from birth due to high testosterone levels.
Mammary glands, in females, contain alveoli, which are lined with cuboidal cells, that secrete milk, and myoepithelial cells. In both males and females, the alveoli (which are only active in females) converge forming lobules (or groups); the lobules drain via a lactiferous duct into the nipple.