||Mam*ma"li*a (?), 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.
&fist; 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.
Hear it pronounced