NUTRITION PROPER. 



315 



fore passed on into the intestines to undergo the third 

 stage of food preparation. There we leave it for the 

 present while we take up the 



Comparative Physiology of the Stomach.— The 



chemical process of digestion is the same, and the appa- 

 ratus nearly the same in all vertebrates. There are 

 only two modifications sufficiently important to arrest 

 our attention — viz., that of ruminant mammals and that 

 of granivorous birds. 



Ruminants. — The stomach of ruminants (Fig. 200) 

 is very complex, and the whole digestive process very 

 elaborate. The stomach consists of four parts — viz.: 



Fig. 200. — Stomach of a sheep, partly cut open so as to show the interior: 

 oe, oesophagus ; v, valvular opening from the oesophagus to the omasum. 



(1) the rumen or paunch; (2) the reticulum or honey- 

 comb ; (3) the psalterium or omasum (psalter, or book, 

 or manyplies) ; and (4) the abomasum or rennet. The 

 rumen or paunch (1) is of immense size, and its func- 

 tion is to store the half-chewed food and soften it by 

 maceration. It is thick and muscular, and constitutes 

 what is called the tripe. The reticulum (2) may be re- 

 garded as an appendage of the paunch, and its function 

 is probably to prepare a macerating liquid and perhaps 

 also to make up the cud-balls. It is full of deep pits, 





