192 



THE VITAL FUNCTIONS. 



spiral fold of the inner, or cuticular membrane, 

 which forms a complete valve, offering no impe- 

 diment to the entrance 

 of food from the oeso- 

 phagus, but obstruct- 

 ing the return of any 

 part of the contents of 

 the stomach into that 

 passage.* This valve 

 is shown in Fig. 311, 

 which represents an 

 inner view of the car- 

 diac portion of the sto- 

 mach of the horse ; o 

 being the termination of the oesophagus. 



The stomach of the Water Rat is composed 

 of two distinct cavities, having a narrow passage 

 of communication : the first cavity is lined ^ith 

 cuticle, and is evidently intended for the mace- 

 ration of the food before it is submitted to the 

 agents which are to effect its digestion ; a process 

 which is completed in the second cavity, pro- 

 vided, for that purpose, with a glandular surface. 

 In proportion as nature allows of greater lati- 

 tude in diet, we find her providing greater com- 

 plication in the digestive apparatus, and subdi- 

 viding the stomach into a greater number of 



* The total inability of a horse to vomit is probably a conse- 

 quence of the impediment presented by this valve. See Mem. 

 du Museum d'Hist. Nat. viii. 111. 



