Structure. 23 



tion from being stopped or interrupted by the rapidity of its 

 motion through a resisting medium. Were it possible for man 

 to move with the swiftness of the Swallow, the actual resistance 

 of the air, as he is not provided with internal reservoirs similar 

 to those of birds, would soon suffocate him.' Another very 

 remarkable peculiarity in the internal economy of birds is their 

 mode of digestion. The bill is scarcely, if ever, used for masti- 

 cation, but solely as an instrument of prehension ; it is the 

 gizzard, whose amazing strength and powers can scarcely be 

 overrated, that grinds down the grain and other food, and renders 

 it fit for digestion. Experiments have been made by which it 

 has been incontrovertibly proved that glass, nails, and the hardest 

 substances have in a few hours been filed down by the action of 

 the gizzard, without any injury accruing to it thereby. As a help 

 to this digestive power small stones are often swallowed by birds, 

 which are eminently useful in assisting this grinding process, 

 thus rendering the food more amenable to the gastric juices. 



After this rapid glance at the general structure of birds, can 

 we conceive anything more adapted for buoyancy and for rapid 

 motion through the air than their external and internal forma- 

 tion ? We cannot but be struck with their wonderful adaptation 

 to the position which they were created to fill. Let us now push 

 our inquiries a little farther ; and still bearing in mind that they 

 are denizens of the air, and roam at vast distances above our 

 heads, and all around us, examine into the senses and faculties 

 with which they are endowed. 



FACULTIES. 



In the first place we shall find them furnished with unusual 

 powers of sight, hearing, and smell ; and to this end they are 

 supplied with three double organs of sense, viz., eyes, ears, and 

 nasal cavities. 



The sight of some, and particularly of the rapacious birds, is 

 so acute and piercing as to enable them to see their prey from 

 an enormous height in the air, whence they dash down with 

 astonishing swiftness and unerring aim. The vulture sailing in 



