NUTRITION PROPER. 3,7 



cud is reduced to a fine, smooth paste, and again swal- 

 lowed. 



Now, when the imperfectly chewed food is swallowed 

 the first time it finds a broad open way to the paunch ; 

 but when, after perfect chewing, it is swallowed the sec- 

 ond time the powerful muscles about the oesophageal 

 orifice of the stomach, by a reflex action little under- 

 stood, contract in such wise as to bring the orifice of the 

 oesophagus directly into contact with the opening into the 

 manyplies, and the food passes into this compartment. 



Evolution of Ruminant Stomach. — We have al- 

 ready seen that the teeth of ruminants were only gradu- 

 ally developed in geologic times from a simple tubercu- 

 lated structure into the complex grinders which we now 

 find. The same is true of the 

 complex stomach, but the evi- 

 dence is less complete, because 

 the stomachs of extinct animals 

 are not preserved. Nevertheless, 

 some stages are still found in ex- 

 isting animals. In all mammals, Fig. 201.— Stomach of a 



, . . . , , . - rat : c, cardiac ; p, py- 



even in man, there is a slight dit- loric portion, 



ference of function in the cardiac 



and pyloric ends of the stomach. In many, as the horse, 

 there is a strong line of demarcation between them. In 

 others, as rodents (Fig. 201), there is a strong hourglass 

 contraction between; but nowhere is the differentiation 

 so marked as in ruminants. 



Granivorous Birds. — The food of grain-eating 

 birds is hard and requires thorough trituration, yet birds 

 have no teeth, and therefore mastication and insaliva- 

 tion can not take place in the mouth. Their food is 

 swallowed whole and insalivated in the crop, and masti- 

 cated in the gizzard. Fig. 202 gives the whole appara- 

 tus. It consists of three parts— viz., (1) the crop (inglu- 



