DIGESTION. 



133 



stomach, a cavity inclosed by thick muscular walls, and lined with a 

 tough and horny epithelium. Here it is subjected to the crushing and 

 grinding action of the muscular parietes, assisted by grains of sand and 

 gravel, which the fowl instinctively swallows with the food, by which it 

 is so triturated and disintegrated, that it is reduced to a uniform pulp, 

 upon which the digestive fluids can effectually operate. The mass then 

 passes into the intestine (<?), where it meets with the intestinal juices, 

 which complete the process of solution ; and from the intestinal cavity 

 it is finally absorbed in a liquid form, by the vessels of the mucous 

 membrane. 



In the ox, the sheep, the camel, the deer, and all ruminating animals, 

 there are four distinct stomachs, each lined with mucous membrane of 

 a different structure, and adapted 



to perform a different part in the Fig-. 27. 



digestive process. (Fig. 27.) The 

 first two, situated side by side at 

 the lower extremity of the oesoph- 

 agus (a), consist of the rumen or 

 paunch (6), a large sac, itself par- 

 tially divided by incomplete par- 

 titions, and lined by a mucous 

 membrane thickly set with long 

 prominences or villi ; and the 

 reticulum (c) or second stomach, 

 so called from the intersecting 

 folds or ridges of its mucous 

 membrane, which give it a reticu- 

 lated or honey-combed appear- 

 ance. Into these two stomachs 

 the food is received when first 

 swallowed by the animal in feed- 

 ing or browsing, and remains 

 there for some time, especially in the capacious rumen, slowly macerated 

 and softened by the action of the warmth and watery fluids, but not 

 undergoing any marked chemical action. When the animal has finished 

 browsing, and the process of rumination commences, the food is regur- 

 gitated into the mouth by an inverted action of the muscular walls of 

 the paunch and oesophagus, and slowly masticated. It then descends 

 again along the oesophagus ; but the lateral opening which communicates 

 with the first two stomachs is now closed by muscular action, and' the 

 oesophagus, thus converted into a tubular canal, conducts the masticated 

 food into a third stomach, the omasus or "psalterium" (d), in which the 

 mucous membrane is arranged in thin longitudinal folds, lying parallel 

 with each other, like the leaves of a book, thus increasing considerably 

 its extent of surface. The exit from this cavity leads directly into the 

 abomasus or "rennet" (e), the true digestive stomach, in which the 

 mucous membrane is soft, thick, and glandular, and in which an acid 



COMPOUND STOMACH OP Ox. a. CEsopha- 

 gua. 6. Rumen, or first stomach, c. Reticulum, 

 or second, d. Omasus, or third, e. Abomasus, 

 or fourth. /. Duodenum. (Rymer Jones.) 



