CLASS SECOND—BIRDS. 
Vertebrated animals with red and warm blood, respiring by lungs, and the 
young of which are produced from eggs. Body covered with feathers, and 
general conformation organized for flying. 
Tue arrangement of birds into orders, has for its basis the conformation 
of the bill and feet; which are adapted to their different modes of living 
and food. Birds of prey are characterized by a hooked bill, and feet armed 
with strong and crooked nails. Climbers are those, the structure of whose 
feet is calculated for motion on an inclined or vertical surface ; and web- 
footed birds are evidently adapted for swimming. Others, again, have the 
legs very long and naked, for wading; and a large number, with the claws 
short and feeble, live chiefly on insects. But though it be thus, easy to 
separate the more strongly marked groups into extended families, yet it 
has been found extremely difficult to distribute them in subordinate groups, 
so as to facilitate the knowledge of species in a class so widely extended. 
In adopting the arrangement of Temminck, therefore, though his orders 
are more numerous, than those proposed by Cuvier and Vieillot, yet the 
families of the latter are in much greater number; and in an elementary 
work, it has been judged proper to follow that system which involves the 
least change of the established nomenclature, ,as likely to be most gene- 
rally useful. 
Birds support themselves, and direct their flight in the air, nearly in the 
same manner as fishes do in the water. But they are also calculated for 
motion on the ground; some families for motion on the surface of the 
water, or even, to a certain degree, through a mass of the same element: 
and their structure is varied to suit these different kinds of motion. 
The part of the spine in birds which corresponds to the back, is immov- 
able, and the only portions of the vertebral column capable of motion, are 
the vertebra of the neck, and those of the tail. Their pectoral members, 
or arms, are elongated to wings, proper only for flight. These members, or 
wings, composed of one long finger and the vestiges of two others, are 
furnished with long, stiff, but elastic feathers, disposed like a fan, which 
follow the movement of the bone, and, when extended, occupy «a large 
surface. The wings are attached by a double clavicle, and are supported 
by a broad sternum, carinated in front like the keel of a ship. This sternum 
is formed of five pieces firmly joined together ; and the greater or less 
ossification of these pieces, is always relative to the powers of the bird for 
