664 DR. C. F. SONNTAG OX THE COMPARATIVE ANATOMY 



as large in the foetus as in the adult. The clifFevence of the 

 small intestine in both stages is not so great, that of the foetus 

 being about four-fifths of the same in the adult. It is also to be 

 remarked that in the foetus the small intestine is considerably 

 longer than the colon, but in the adult the reverse is the case. 

 The differences can of course be ascribed to the diiference of the 

 diet of both stages. The milk food of the mammary foetus is 

 chiefly or completely digested in the small intestine, but the 

 vegetable diet of the adult needs a greatly developed csecum and 

 colon. The longitudinal folds of the csecum and colon are, 

 however, already developed in the foetus." 



It is possible that the growth of the intestinal tract in my 

 specimen has been considerably retarded. 



Ellenberger, Tullberg, and Lonnberg believe that the large 

 size of the cascum in many animals, such as the Horse, Koala, 

 and some Rodents, is brought about by the presence of a large 

 amount of cellulose in the diet ; and when the small intestine 

 deals with all the elements of the food, there is no specialisation 

 in the csecum and colon. Lonnberg also speculates about the 

 great length of the small intestine in phyllophagous Mammals. 

 He states that the leaves consist of cellulose and certain proto- 

 plasmic, amylaceous, and other substances contained within 

 resistant envelopes. Some time must elapse, therefore, before 

 these are broken down and their contents become available for 

 digestion and absorption ; the small intestine is, consequently, 

 long. 



Lonnberg's views, however, will not account for the conditions 

 present in the intestinal tract of the phyllophagous Three-toed 

 Sloth {Bradypits tridactylits). In my paper dealing with its 

 anatomy (18), I showed that the intestinal tract is short, the 

 ciBcal pouch is rudimentary, and the interior of the colon and 

 rectum offers a large absorptive area, due to the excavation and 

 folding of the mucous membrane ; it possesses sphincters which 

 are similar in character -to, but larger than, those of the csecum of 

 TrichosiLvus vulpecula, and its muscular coat, Avhich thickens 

 from before backwards, may have a similar function to that of 

 the csecum of T. vulpecula. 



Although the stomach of B. tridactylus contains many hard, 

 almost entire leaves, the intestinal tract contains none, so the 

 cellulose and hard materials have been completely comminuted 

 and reduced to the state of chyme; Rapp's analogies are interest- 

 ing in this connection, for he likens the paunch and pylorus to a 

 crop and gizzard. This thorough digestive process must throw 

 less work on the small intestines, which, in consequence, are short. 



The chyme yields a number of substances for absorption in the 

 small intestines, and the remainder is absorbed from the large 

 intestines, whose pockets and sphincters retain it in the colon 

 and rectum, and the muscular coat moves it backwai'ds and 

 forwards ; and the sphincter ani has a retaining function similar 

 to that of the septa higher up in the colon. 



