mammary gland mammary gland a mammary gland is an exocrine gland in humans and other 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, sheep, 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. with humans, male lactation can occur only under specific circumstances. mammary glandcross-section of the human mammary gland. chest wallpectoralis muscleslobulesnippleareolamilk ductfatty tissueskindetailsprecursormesoderm (blood vessels and connective tissue)ectoderm (cellular elements)arteryinternal thoracic arterylateral thoracic arteryveininternal thoracic veinaxillary veinnervesupraclavicular nervesintercostal nerves (lateral and medial branches)lymphpectoral axillary lymph nodesidentifiersta98a16.0.02.006ta27099fma60088anatomical terminology mammals are divided into 3 groups: prototherians, metatherians, and eutherians. in the case of prototherians, both males and females have functional mammary glands, but their mammary glands are without nipples. these mammary glands are modified sebaceous glands. concerning metatherians and eutherians, only females have functional mammary glands. their mammary glands can be termed as breasts or udders. in the case of breasts, each mammary gland has its own nipple (e.g., human mammary glands). in the case of udders, pairs of mammary glands comprise a single mass, with more than one nipple (or teat) hanging from it. for instance, cows and buffalo each have one udder with four teats, whereas sheep and goats each have two teats protruding from the udder. these mammary glands are modified sweat glands. structure