DIGESTIVE APPARATUS OF BIRDS 



299 



Digestive Apparatus of the ComtLon ~Fo\ 



digestion, the gullet presents no enlargement ; while in the eagles 

 and vultures, which gorge themselves at uncertain intervals 

 from bulky carcasses, it undergoes a lateral dilatation, to serve 

 as a temporary reservoir or macerating apparatus. 



In those birds whose food consists of grains and seeds this 

 enlargement or crop is still further developed, and assumes the 

 form of a large-sized single 

 pouch (6), as in the fowl, 

 or of a double one, as in 

 the pigeon. Here the 

 food will frequently re- 

 main for sixteen or twenty 

 hours, until it becomes 

 softened with the abundant 

 secretion of the salivary 

 glands ; and being thus 

 duly prepared, it passes on 

 to the proventriculus (c), 

 the first or glandular divi- 

 sion of the stomach, where 

 it is submitted to the solvent action of the gastric juice. The 

 proventriculus varies in form and magnitude in different birds, 

 but is largest in those which have no crop, as if to compensate 

 for the want of this preparatory macerating cavity. 



The third and last act of the digestive process is performed 

 in the gizzard (e\ which 

 in the birds of prey as- 

 sumes the form of a mere 

 membranous sack, in 

 accordance with the ani- 

 mal and easily digesti- 

 ble nature of their food ; 

 but in those which de- 

 vour thick-coated seeds 

 or other hard substances, 

 it is of so dense a texture, 

 that its horny callous 

 sides (gg) are able to 

 grind the aliments as 

 between two millstones. Gizzard of a s\\ an. 



