526 



DIGESTION. 



Fig. 228. 



passage through the first two. In the third and fourth stomachs, more 

 especially the latter, true digestion takes place. When the food is of 

 such a character as not to require rumination, it can be sent on directly 

 into the third stomach, by the arrangement just described. 



In the bird tribes, we see an admirable adaptation of structure to 

 the functions which the digestive organs have to execute. Animals 

 of this class may be divided into the granivorous and the carnivorous. 

 It is in the former, that we are so much impressed with the organiza- 

 tion of this part 

 of their economy. 

 The grain on which 

 they feed, although 

 more nutritious 

 than grass, which 

 constitutes the ali- 

 ment of the herbi- 

 vorous quadruped, 

 requires equal diffi- 

 culty in being assi- 

 milated to the na- 

 ture of the being 

 it has to nourish. 

 Added to this, it 

 is in such a condi- 

 tion, that the juices 

 of the digestive or- 

 gans cannot rea- 

 dily act upon it. 

 The bird having no 

 masticatory appa- 

 ratus within the 

 mouth, the grain 

 must of necessity 

 be swallowed whole. 

 But we find that 

 lower down in the 

 alimentary tube, a 

 powerful mastica- 

 tory apparatus ex- 

 ists, which has fre- 

 quently been con- 

 sidered as a part 

 of the digestive sto- 

 mach ; but really seems destined for mastication only. The following 

 is the arrangement of their gastric apparatus. 



The oesophagus terminates at the bottom of the neck in a large sac 

 ingluvies, crop or craw which is of the same structure with the 

 oesophagus, but thinner. On the inner side of the crop are numerous 

 glands, with very distinct orifices in large birds, which secrete a fluid 

 to assist in the solution of the food. To the crop succeeds another 



Gastric Apparatus of the Turkey. 



