VI. Belluæ.—Having blunt wedge-shaped front teeth in both jaws; and the feet with hoofs, as horses.
VII. Cetacea.—Having spiracles or breathing-holes on the head; fins instead of fore feet; and a tail flattened horizontally, instead of hind feet. This order consists of the narvals, whales, cachalots, and dolphins.
ORDERS OF BIRDS.
The second class, or Birds, comprises all such animals as have their bodies clad with feathers. Their jaws are elongated, and covered externally with a horny substance, called a bill or beak, which is divided into two parts called mandibles. Their eyes are furnished with a thin, whitish, and somewhat transparent membrane, that can at pleasure be drawn over the whole external surface like a curtain. Their organs of motion are two wings and two legs; and they are destitute of external ears, lips, and many other parts which are important to quadrupeds. That part of Zoology which treats of Birds is called Ornithology.
Linnæus divided this class into six Orders:
1. Land Birds.
I. Rapacious Birds (Accipitres).—Having the upper mandible hooked, and an angular projection on each side near the point, as the eagles, hawks, and owls.
II. Pies (Picæ).—Having their bills sharp at the edge, somewhat compressed at the sides, and convex on the top, as the crow.
III. Passerine Birds (Passeres).—Having the bill conical and pointed, and the nostrils oval, open, and naked, as the sparrow and linnet.