KIRDS. 555 



In their formation a new, and in as far as relates 

 to the organs of progressive motion, a more de- 

 veloped type is adopted ; still preserving a con- 

 formity with the general plan of the vertebral 

 organization, and with the general laws of its 

 developement. 



The skeleton of birds has the same constituent 

 parts as that of other vertebrated classes : the 

 bones of the anterior extremity, though destined 

 exclusively to support the wing, retain the same 

 divisions, and are composed of the usual ele- 

 ments : and the general form of the body is that 

 best calculated to glide through the air with the 

 least resistance. As birds swallow their food 

 entire, there is no necessity for any part of the 

 bulky apparatus of hard and solid teeth, large 

 muscles and heavy jaws which are required by 

 most quadrupeds : hence the head admits of 

 being greatly reduced in its dimensions; and 

 the form of the beak, which is drawn to a point, 

 and cuts the opposing air, tends to facilitate the 

 progress of the bird in its flight. 



In the conformation of the body, also, every 

 circumstance that could contribute to give it 

 lightness has been sedulously studied. The 

 general size of birds is considerably smaller 

 than quadrupeds of corresponding habits. No 

 where has Nature attempted to endow a huge 

 ponderous animal, like the fabled Pegasus, 

 with the power of flight. Great condensation 



