ON THE INTESTINAL TRACT OF MAMMALS. 183 



6. Further Observations on the Intestinal Tract of Mammals.. 

 By P. Chalmers Mitchell, M.A., D.Sc, LL.D.^ 

 F.R.S., Secretary to the Society. 



[Received January 31, 1916 : Read Februaiy 22, 1916.] 



(Text-figures 1-30.) 



Index. 



Anatomy and Morphology : Page 



Gut-patterns of Mammals 183 



Primitive Mammalian gut 185 



Gut-Datterns of Monotremata 189 



Marsupialia 190 



Edentata 199 



Hj'racoidea 202 



Proboscidea 210 



Cetacea 211 



Artiodactyla 213 



Perissodactyla 221 



Rodentia 223 



Insectivora 226 



Chiroptera 229 



Carnivora 232 



Prosimias 237 



Simia- 240 



General Conclusions 241 



Systematic Inferences 245 



List of References 250 



In this communication I describe the gut-patterns of certain 

 mammals that I have been able to examine since the publication 

 of a larger memoir on the Intestinal Tract of Mammals (Mitchell^ 

 1905), and I discuss further the significance of the facts with which 

 I am dealing. I adhere to the purpose stated in the introduction 

 to my memoir, to " limit my observations to a definite set of 

 facts, hoping that the examination of a continuous series by one 

 observer, from one point of view, would yield more information 

 than might be derived from a wider range of work over a smaller 

 range of animals." My object wa,s to approach a conception of 

 the primitive pattern of the mammalian gut, to show how the 

 complex patterns in the different groups were related to the 

 primitive pattern, and to discuss how far such relations throw 

 light on the systematic affinities of the groups. 



In certain cases, most common in the lower types of mammals, 

 there is no difficulty in observing the pattern. When the gut is 

 severed near the stomach and at the distal end of the rectum, 

 there remains only to cut the dorsal mesentery from the rectum 

 to the stomach and to sever the portal vein and mesenteric 

 arteries ; the whole structure of intestinal tract, mesentery, and 

 blood-vessels may then be pinned-out on the dissecting-board 

 and the pattern observed without fur'ther trouble. Text-fig. 27 



