Q 2 THE ANIMAL KINGDOM. 



moral attributes by which he can raise his thoughts and 

 aspirations to a world above. It is not intended to enter 

 hej-e on the study of Human Physiology ; an elementary 

 treatise on this subject has already been issued,* and 

 further instruction will be given in a future volume. 



BIRDS. 



THE second great division of the Vertebrata compre- 

 hends animals whose fore limbs are converted into wings, 

 by which they are enabled to fly in the air. Their whole 

 structure is of exceeding lightness : the air not only 

 enters their lungs, but is conveyed to the interior of their 

 bones, and thus assists them in rising and in sustaining 

 themselves in the atmosphere. 



Their blood is hot, and very rapid in its circulation, and 

 it is this which renders them so peculiarly active. Their 

 covering, too, adds but little to their weight, for every 

 feather contains air. 



Birds are entirely devoid of teeth. Those that feed on 

 flesh have a very strong and sharp beak, which in some 

 cases is jagged at its edge, so that they can cut or tear 

 their prey ; those which feed on grain have a hard mus- 

 cular stomach, called the gizzard, in which the food is 

 ground by the gravel, &c. 4 , which the fowl has swallowed. 

 The beaks and feet of birds arc as wonderfully adapted to 

 their modes of life as are the teeth and feet of mammalia ; 

 and as they vary in every order, they will be described in 

 their proper places. 



The collar-bones unite in the form somewhat like the 

 letter V, and make up the bone known as the merry- 

 thought; this keeps the shoulders well apart, and affords 

 support to the socket in which the bones of the wings work. 

 Their eyes are protected by a third eyelid, which moves 



* " Our Bodies," Cassell's Primary Scries. 



