22 Introduction. 



rather to rival the velocity of the arrow from the bow than the 

 movements of any other creature. Yet, with such amazing 

 power, what can be lighter than the materials of which the 

 wings are formed? the bones hollow and filled with air, the 

 muscles strong and unencumbered by flesh, the feathers large, 

 like sails, and of exceeding buoyancy. Then again, in like 

 manner, what can be more perfect than their tails ? These, too, 

 are only composed of feathers, but they serve as rudders, enabling 

 them to steer their course through the air at pleasure, with the 

 greatest ease and with the greatest accuracy. 



Thus, when we look at the external formation of a bird, we can 

 but admire its symmetry and elegance, the buoyancy and light- 

 ness of its frame, so admirably adapted for flight ; but not less 

 perfect nor less calculated to excite our admiration in its internal 

 structure. Is a bird furnished with bones and muscles so abso- 

 lutely necessary to its aerial evolutions ? But mark how thin 

 and light are the bones, how delicate the muscles, those only 

 excepted which are adapted for moving the wings. Then, again, 

 observe the lungs. Small, indeed, they are, but so placed, and 

 the air so introduced into them from the windpipe, that in 

 passing it is conveyed into certain cells or membranous sacs 

 disposed for this purpose over the body. These sacs are situated 

 in the chest and among the muscles, and between the muscles 

 and the skin ; and in some birds are continued down to the 

 wings, and extend even to the pinions, thigh bones, and other 

 parts of the body. For the same purpose the feathers, and 

 especially the wing feathers, also contain a large quantity of air. 

 Now all these cavities, and others not enumerated, such as the 

 hollows of the bones, can be filled and distended with air at the 

 will of the bird. By this means the strength and bulk of the 

 bird is increased, without adding to its weight ; and such a 

 general diffusion of air throughout the body must be of infinite 

 service in enabling it to fly, to poise itself in the air, and to skim 

 far above the surface of the earth. Nor is that the only use of 

 this wonderful provision of nature. I again quote Bewick, who 

 says : ' It is likewise eminently useful in preventing its respira- 



