VI PREFACE. 



With respect to the particular shape of the 

 feathers themselves, they vary greatly in the 

 different tribes. 



The particulars most important in the com- 

 parative anatomy of birds are these. The 

 heart is furnished with two cavities, or, in the 

 language of anatomists, is bilocular, and the 

 general course of the circulation is carried on 

 as in quadrupeds. The lungs are very large, 

 affixed to the back part of the cavity of the 

 breast, and are furnished with several external 

 orifices, by which the air they contain is at 

 pleasure communicated to other parts of the 

 frame. The throat, after passing down to a 

 certain distance, dilates into a large mem- 

 branaceous bag, answering to the stomach in, 

 quadrupeds: it is called the crop, and its 

 great use is to soften the food taken into it, 

 in order to prepare it for passing into another 

 stronger receptacle called the gizzard: this, 

 which may be considered as a more powerful 

 stomach than the former, consists of two very 

 strong muscles, lined and covered with a- 

 stout tendinous coat, and furrowed on the 

 inside: in this receptacle the food is com- 

 pletely ground, and reduced to a pulp: in 



