206 THE VITAL FUNCTIONS. 



length of the canal, so that the internal surface 

 is much augmented without any increase in the 

 length of the intestine.* 



When the nature of the assimilatory process 

 is such as to require the complete detention of 

 the food, for a certain time, in particular situa- 

 tions, we find this object provided for by means 

 of caca, or separate pouches, opening laterally 

 from the cavity of the intestine, and having no 

 other outlet. Structures of this description have 

 already been noticed in the Infusoria f ; and they 

 are met with, indeed, in animals of every class, 

 occurring in various parts of the alimentary tube, 

 sometimes even as high as the pyloric portion of 

 the stomach, and frequently at the commence- 

 ment of the small intestine. Their most usual 

 situation, however, is lower down, and especially 

 at the part where the tube, after having remained 

 narrow in the first half of its course, is dilated 

 into a wider cavity ; which is distinguished from 

 the former by the appellation of the great intes- 

 tine, and which is frequently more capacious 

 than the stomach itself. It is exceedingly pro- 

 bable that these two portions of the canal per- 

 form different functions in reference to the 



* Structures of this description have a particular claim to 

 attention from the light they throw on the nature of several 

 fossil remains, lately investigated with singular success by Dr. 

 Buckland. 



t Page 96, of this volume. 



