236 DR. p. CHALMERS MITCHf:LL OX THE 



region is rather distinct from Meckel's tract. The latter forms 

 the longest part of the gut, but is relatively shorter than in most 

 types of mammals. It is thrown into rather simple minor loops 

 which reach to the extremity of the proximal limb of the pendant 

 loop, but in the recurrent limb are replaced by an almost straight 

 portion running up towards the duodenum. The cpecum is 

 situated high up on the recuri-ent limb, and in Proteles is short, 

 iilthough in the example I examined it was not so globular as 

 was described by Flower (Flower, 1869), and had a slight spiral 

 twist not noted by that author. The axis of the twist was con- 

 nected with the distal extremity of the ileum by a very small 

 fold of mesentery. The csecnm is frequently absent in Garnivoi-es, 

 but when present, and especially when it is relatively not very 

 small, frequently displays a spiral twisting. 



Distad of the cfecum the hind-gut bends round sharply, 

 increasing in calibre and di,splaying a rather considerable 

 expansion before it passes into the short straight rectum. The 

 hind- gut is relatively short in all the Carnivores, and a notable 

 feature is the reduction or absence of the transverse colon, the 

 recurrent limb of the pendant loop bending round to pass back- 

 wards either with a very sharp turn, or at most a nari'ow sweep. 

 From re-examination of all my original laborator}' notes and 

 drawings, I am disposed to think that at least in the great 

 majority of Carnivores the expansion of the hind-gut, when 

 present, belongs to the portion of the gut distad of the pendant 

 loop, and is therefore an ansa coll sinistra not homologous with 

 colic loops developed on the recurrent limb of the pendant 

 loop. 



In the Bears, however, as I liave already shown (Mitchell, 

 1905, fig. 34), there is a definite colic loop present, and as this is 

 an expansion of the recurrent limb of the pendant loop, it must 

 be regarded as an ansa coli dea'tra. In the new-born cub of a 

 Brown Bear, this loop was more definite and more elaborate than 

 in the example of Urstis malayanus that I formerly figured. 

 The Otter shows a somewhat similar condition. There was no 

 trace of any secondary connection linking the colic region to the 

 duodenum. 



The primitive mesentery is retained in a nearly complete 

 condition in most Carnivores, and in association with the 

 relative shortness of the gut in the terrestrial forms, secondaiy 

 attachments between proximal and distal portions of the gut 

 appear to vary even individually, and nevei- attain the physio- 

 logical importance that they may be presumed to have in many 

 other groups. As I have already stated, I do not believe them 

 to have systematic importance. 



It is clear that the Pinnipedes and Fissipedes exhibit gut- 

 patterns that are fundamentally similar, although the resem- 

 blance is decreased by the adaptive lengthening of the gut in 

 the aquatic forms. 



