42 ZOOLOGY. 



the amylaceous and fatty bodies which had resisted the action 

 of the gastric juice are now acted on by the bile and pancreatic 

 juice ; and various gases are disengaged from the alimentary 

 mass distending the intestine. These gases are chiefly car- 

 bonic acid gas and hydrogen ; sometimes nitrogen. Finally, 

 the more fluid parts of the chymous mass are absorbed by the 

 lacteals, which become rarer and rarer towards the lower 

 portion of the small intestine, until they are no longer to be 

 found, and the mass formed by the remains of the chyme, by 

 the bile, and other humours already mentioned, acquires in 

 this portion of the tube more consistence, assumes a brown 

 colour, and thus passes into the large intestine. 



Expulsion of the Residue left after Digestion. 



72. The alimentary matters which do not admit of 

 digestion require to be expelled from the body. For this 

 purpose they are collected into the large intestine. 



The Large Intestine (Fig. 32) is continuous with the 

 small, and in most mammals is easily distinguished from it 

 by its irregular cellular aspect. Anatomists divide it into 

 caecum, colon, and rectum. The caecum,* situated in the 

 right iliac region, is prolonged into a cul de sac, beyond the 

 point of insertion of the small intestine. At its lower ex- 

 tremity it communicates with a small tube, the appendix 

 vermiformis, which may be considered as a prolongation of 

 the caecum. A very perfect valve, formed of folds, and 

 situated internally at the junction of the small intestine 

 with the large, is placed so as to prevent or impede the 

 return of whatever has passed from the small into the larger 

 bowel. 



The colon is a continuation of the caecum. It traverses 

 the abdomen immediately beneath the stomach, gains the 

 left side, and, descending to the edge of the pelvis, is con- 

 tinuous with the rectum. This latter terminates at the 

 anus. 



73. The residue of the food passing from the caecum 

 and colon to the rectum, remains there for a certain time. 

 The matter has now acquired considerable consistence and a 

 peculiar odour. Gases are developed which differ from those 



* The ceecum (cacus, blind) forms a cul de sac at the commencement of the 

 large intestine. 



