DIGESTION. 



117 



glandular, and is provided with numerous se- 

 creting follicles or crypts. From them an 

 acid fluid is poured out, by which the food is 

 subjected to further changes. It next passes 

 into the gizzard (d), or triturating stomach, a 

 cavity inclosed by thick muscular walls, and 

 lined with a remarkably tough and horny 

 epithelium. Here it is subjected to the crush- 

 ing and grinding action of the muscular pa- 

 rietes, assisted by grains of sand and gravel, 

 which the animal instinctively swallows with 

 the food, by which it is so triturated and dis- 

 integrated, that it is reduced to a uniform pulp, 

 upon which the digestive fluids can effectually 

 operate. The mass then passes into the intes- 

 tine (e), where it meets with the intestinal 

 juices, which complete the process of solution ; 

 and from the intestinal cavity it is finally ab- 

 sorbed in a liquid form, by the vessels of the 

 mucous membrane. 



In the ox, again, the sheep, the camel, the 

 deer, and all ruminating animals, there are 

 four distinct stomachs through which the 

 food passes in succession; each lined with 

 mucous membrane of a different structure, 

 and adapted to perform a different part in 

 the digestive process. (Fig. 17.) When first 

 swallowed, the food is received into the ru- 

 men, or paunch (b), a large sac, itself par- 

 tially divided by incomplete partitions, and 

 lined by a mucous membrane thickly set 

 with long prominences or villi. Here it ac- 

 cumulates while the animal is feeding, and is 

 retained and macerated in its own fluids. When the animal has 

 finished browsing, and the process of rumination commences, the 

 food is regurgitated 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 instead of enter- 

 ing the first stomach, as before, it is turned off' by a muscular valve 

 into the second stomach, or reticulum (c), which is distinguished 

 by the intersecting folds of its mucous membrane, which give it 



ALIMENTARY CASAL OF 

 FOWL. . (Esophagus. b. 

 Crop. c. Proventriculus, or 

 secreting stomach, d. Gizzard, 

 or triturating stomach, e. In- 

 testine. /. Two long csecal 

 tubes which open into the in- 

 testine a short distance above 

 its termination. 



