248 NATURAL THEOLOGY 



VIII. 



THE RELATION OF THE BODIES OF BIRDS TO THE 

 ATMOSPHERE. 



The first object noticed in Chap. xvii. is the 

 wing of a bird ; and this is given as an instance of 

 the relation of the animal body to the elements by 

 which it is siirromided. We entreat our readers' 

 attention to the philosophy of this subject. And 

 let us not be contented with admiring the struc- 

 ture of the feather, or the adaptation of the bones 

 of the wing to their office, but let us go deeper into 

 the inquiry : it is a subject which will reward us. 



Let us take it for granted that a creature is to 

 live by the exercise of the same functions with the 

 races of mammalia or quadrupeds, as digestion, 

 assimilation, respiration <tc. ; but that it must rise 

 in the air and seek its f c d bv long flights. What 

 are the circumstances necessc*jy to this new con- 

 dition 1 Is it not obvious that the creature must 

 be specifically lighter or more buoyant in the at- 

 mosphere? — that instead of its muscular system 

 being divided and directed to the movement of 

 four extremities, it must have its strength princi- 

 pally directed to the wings, that it may extend 

 them and be able to raise its body upon them? 

 Let us then see how this is accomplished, and how 



