204 DR. P, CHALMERS MITCHELL ON THE 



the recurrent limb of mammals generally, and bearing on this a 

 symmetrically placed pair of conical cseca, which I take to be the 

 representatives of the normal mammalian cajca, paired as they 

 are in some Edentates and in the Manatee. Distally the large 

 intestine forms first a colic loop, thrown into minor folds, from 

 its position to be regarded as an ansa colt sinistra, and a rather 

 long rectal portion. The posterior mesenteric vein, supplying 

 the distal portion of the hind-gut, has to be severed in order to 

 lay out the intestinal tract in the fashion of this memoir, and its 

 cut ends are indicated at XX, in text-fig. 12. 



The difficulty in interpreting the gut-pattern of Hyrax comes 

 about from the presence of the csecal pouches. The small pouch, 

 marked 0. 3 in the diagram, appears to be more due to the con- 

 traction of the gut immediately proximad of it than to any 

 special outgrowth of the gut itself, and as it is absent in at least 

 one species of Hyrax, I regard it as a character without morpho- 

 logical significance. The very large thin -walled pouch marked 

 A.C. is present in all the species that have been examined. It 

 is a large thin- walled sac somewhat puckered by two bands 

 of muscle which, when it is fully expanded, give it an almost 

 bi-lobed appearance, somewhat exaggerated in the figure of 

 Hyrax capensis in my earlier memoir (Mitchell, 1905, p. 461). 

 The entrance and the exit of the gut lie close together at the 

 proximal end. 



The entrance of the gut into the accessory cjecum is protected 

 by a raised lip. George (1874, pi. 13. fig. 3), who regarded the 

 accessory csecum as the true csecum, calls this entrance of the 

 gut into it the ileo-csecal valve, and figures it as guarded by a 

 flap so placed as to prevent the passage of the contents of the 

 fore-gut into the ctecum. I found no trace of such a structure, 

 and I do not understand how, if it were present, it could act. 

 On the other hand, the arrangement I found, by the contraction 

 of the lip, would prevent the regurgitation of the contents of 

 the cascum into the proximal pai't of the intestinal tract. The 

 ajDerture of exit leading to the distal portion of the gut is wider, 

 and is surrounded by a shallower lip. The portion of the intes- 

 tine into which it leads is closely adherent to the wall of the 

 caecum, and the cavity is at first slightly convoluted, forming 

 what might be described as a separate chamber of the ca;cum, 

 but in H. do7'salis this is not so well marked as in the figure 

 given by George (1874, pi. 13. tig. 4). There is a general 

 resemblance between this caecum and the normal caeca of those 

 mammals in which the caecum is capacious and relativel}'- short. 

 The normal cfecum of mammals, however, always appears to 

 be a forward continuation of the hind-gut, the one cavity being 

 directly continuous with the other in the simplest fashion, except 

 in those cases in which it is slightly complicated by vestiges of the 

 presence of the second caecum of an original pair. This is unlike 

 the complicated relation of the unpaired caecum of Hyrax to the 

 ^ut that leaves it. A comparison has been made between this 



