NATURAL HISTORY.
MAMMALIA.
The Class of animals of which the present volume is intended to treat, comprises those which have an internal jointed skeleton of bone; which breathe by means of lungs, through which the whole blood passes at each circulation; and which bring forth and suckle living young.
In common language this class is denominated Quadrupeds or Beasts; terms, which, though sufficiently appropriate as indicating the great majority of its subjects, are not in strictness applicable to it as a whole; for, though the general character of the animals of this division is to possess four extremities, in one important Order, that of the Whales (Cetacea), the hinder pair of limbs is altogether wanting, or only exists in a rudimental condition. The fish-like forms and aquatic habits of these exclude them from the common notion of "Beasts," as much as the absence of hind feet from that of "Quadrupeds;" yet in all characters which are really essential, they do not deviate from the ordinary members of the Class we are
