n. pl.

[NL., from L. mammalis. See Mammal.]
(Zoöl.) The highest class of Vertebrata. The young are nourished for a time by milk, or an analogous fluid, secreted by the mammary glands of the mother.

Note: Mammalia are divided into three subclasses; --

I. Placentalia. This subclass embraces all the higher orders, including man. In these the fetus is attached to the uterus by a placenta.

II. Marsupialia. In these no placenta is formed, and the young, which are born at an early state of development, are carried for a time attached to the teats, and usually protected by a marsupial pouch. The opossum, kangaroo, wombat, and koala are examples.

III. Monotremata. In this group, which includes the genera Echidna and Ornithorhynchus, the female lays large eggs resembling those of a bird or lizard, and the young, which are hatched like those of birds, are nourished by a watery secretion from the imperfectly developed mammæ.

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A cynical view of the world by Ambrose Bierce

n.pl.

A family of vertebrate animals whose females in a state of nature suckle their young, but when civilized and enlightened put them out to nurse, or use the bottle.

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IN BRIEF: n. - Warm-blooded vertebrates characterized by milk glands in the female.