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438 DR. P. CHALMERS MITCHELL OX THE 



Introduction. 



ALTHOUGH there is a considerable literature on the Intestinal Tract of Mammals, 

 much of it gained from observations made from animals in the Collection of this 

 Society, it has been impossible hitherto to gain a survey of the modifications presented 

 by the tract in the whole group. Some observers have described with varying detail 

 the complete abdominal viscera of a larger or smaller number of animals. Others have 

 limited their subject and extended their area. But, even in the latter case, it has 

 frequently happened that in one animal the stomach, in another the liver, in a third 

 the csecum has absorbed the attention of the anatomist. The result is that whilst 

 there is a great deal of scattered information, the changing interest of single observers 

 and tbe diverse points of view of different observers have made the assemblage of facts 

 extremely difficult to compare. From time to time, in the last six or seven years, I 

 have made what use I could of the rich material in the Prosectorium of tbe Society, 

 and. following the method which I found of service in the case of the Intestinal Tract 

 of Birds, I have limited 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 number of animals. I have thus been able to cover a very considerable 

 proportion of the existing mammalian types. The figures which illustrate this 

 Memoir are prepared from a much larger number of laboratory drawings. Naturally 

 they are to a certain extent diagrammatic, but I believe that in the main they give a 

 faithful representation of the essential facts. 



In the systematic part, I have followed closely the classification given by Weber (27). 

 As for the nomenclature of individual animals, I have not attempted to follow the 

 names on which modern systematists are beginning to agree. In nearly every case I 

 have used the name given by my predecessor, Dr. P. L. Sclater, in the ninth edition 

 of the ' List of the Vertebrated Animals now or lately Living in the Gardens of the 

 Zoological Society of London.' 



Morphology of the Intestinal Tract. 



The work of Toldt (26) chiefly on Man, of Klaatsch (11) chiefly on Keptiles and 

 Mammals and relating in particular to the mesenteries, of Mathes (13) on Amphibia, 

 and my own work on Aves (15) have paved the way for the general comprehension of 

 the morphology of the intestinal tract in Mammals. The primitive gut ran backwards 

 from the stomach to the cloaca suspended from the dorsal wall of the body-cavity by a 

 dorsal mesentery. This tract, ontogenetically and phylogenetically, becomes longer 

 than the straight length between its extreme points, and consequently is thrown into 



