CHAP.XXV.] THE INTESTINAL CANAL IN VERTEBRATA. 22 1 



the rat, the coecum is of small dimensions. The whole large intestine is cellula- 

 ted, the cells being formed by longitudinal fibres and circular constricting ones. 



In the genus Myoxus (dormouse), the coecum is entirely absent, the only excep- 

 tion according to Meckel, to the presence of this cavity in the rodent order. 



In the Marsupiate animals, the distinction between large and small intestine 

 is clearly marked by the presence of a ccecum. The small intestine is long, 

 and in some very wide ; the coecum is of moderate length and width, its ca- 

 pacity being much below that of the stomach. 



The chief peculiarity of the intestinal canal in the Monotremata is to be found 

 at its inferior extremity, where a cloaca exists common to the rectum with the 

 urino-genital organs. A small ccecum separates the long and small intestine. 



The Cetaceous mammalia, have an intestinal of considerable length. The 

 length of the canal in the zoophagous cetacea is to that of the body as eleven 

 or twelve to one. (Meckel.) According to Cuvier, the proper whales have no 

 division between large and small intestine, and consequently no coecum. This 

 is the case in the porpoise. In the Balwna Rostrata, however, according to 

 Hunter, and in all the Balance, according to Cuvier, a small coecum, not unlike 

 that of carnivora, exists. In the herbivorus cetacea the intestinal canal is of pro- 

 portionately greater length than in the zoophagous cetacea. In the Dugong, 

 according to Meckel, its length exceeds forty times, and in the Lamantin of 

 Kamtschatka, twenty times that of the body. 



The Quadrumana. The length of the intestinal canal in this large order of 

 Mammifers presents very remarkable variety, which is the more curious as the 

 nature of the food is, with few exceptions, similar in the various genera. The 

 proportion of the length of the intestinal canal to that of the body is in some 

 as eight to one, whilst in others it is only as three to one.* The division into 

 two portions is effected in the same manner as in the human subject, and the 

 general arrangement of both small and large intestine is very similar to those 

 of man. A coecum exists in all the genera, but presents considerable variety 

 as to length ; an increased length of this portion of intestine along with a 

 larger development of the splenic extremity of the stomach being employed in 

 some cases to compensate for a deficiency in the length of the intestinal canal. 

 The Orangs and Gibbons have the peculiarity, which they alone possess in 

 common with man, of a process from the coecum, some inches in length, de- 

 nominated the vermiform appendix. 



From the preceding brief review of the anatomical characters of the intes- 

 tinal canal in the vertebrate classes, we gather, that this portion of the digestive 

 tube diminishes in complexity as we descend from mammalia to fishes ; that a 

 short and simple intestinal canal is generally co-existent with a diet of animal 

 food ; and, on the other hand, that a diet of vegetable food, or a conjoint animal 

 and vegetable diet requires greater length and greater complexity in the form 

 and structure of the intestines. In estimating the length of the intestinal canal 

 we must not confine our examination to a mere external measurement, as we 

 should thereby be led to a very erroneous conclusion. Deficiency in length, as 

 measured on the exterior of the intestine, may be supplied by increased width 

 by a more highly developed state of the villi of the mucous membrane by 

 numerous folds of that membrane, and the energy of the action of the mucous 

 membrane on the contents of the intestine may be augmented by the greater 

 number and size of the glands which pour out their secretions on its surface. 



* Vide a table in Meckel's Anat. Comp. (French Ed.) torn. viii. p. 778. 



