208 DR. p. CHALMERS MITCHELL ON THE 



case of the unpaired caecum of Hyrax, yet present in Perissodac- 

 tyles, as in most other mammals. That there is in Perisso- 

 dactyles (see infra, p. 222) also an adventitious set of fibres 

 binding the true csecum to the proximal end of the hind-gut, 

 affords no indication of affinity. Another secondary ligament 

 stretches from the duodenal region to the portion of the gut 

 immediately distad of the paired cseca of Hyrax (Bedda.rd, 1908, 

 text-fig. 115, c.d.). The possibility of this attachment being 

 formed depends, in my opinion, on the fact that at this point 

 the recurrent limb of the pendant loop nearly reaches the dorsal 

 middle line, and therefore approaches the duodenum very closely. 

 If any importance can be attached to its presence, it clearly 

 marks the region just distad of the paired cseca as the beginning 

 of the hind-gut, and corroborates my orientation of the gut. A 

 third secondaiy ligament well developed in the Hyracoidea is that 

 between the omentum and the t]-ansverse colon (Beddard, 1908, 

 text-fig. 115. O.). This also, so far as any significance can be 

 attached to its presence, identifies this portion of the gut, distad 

 of the paired ceeca, and indicates the homology of these organs 

 with the normal mammalian csecum. Dr. Beddard himself sees 

 the weight of this objection to his argument, but endeavours to 

 get out of the difficulty by discussing the varying disposition of 

 the corresponding attachments in different Rodents. When one 

 is ti-ying to prove the affinity of Hyrax with the Rhinoceros on 

 the ground of the attachment of certain ligaments, the argument 

 does not appear to be much strengthened by showing that these 

 attachments are not the same in Dasyprocta as in other Rodents. 



So far as I am able to follow it. Dr. Beddard's third point, 

 relating to the presence of an ansa 2yciTa,cmcalis in Hyrax com- 

 parable with the ansa paraccecalis of Perissodactyles is uncon- 

 vincing. The portion of gut (Beddard, 1908, text-fig. 113, ^. a.) 

 which he thus designates in Hyrax, just distad of the un- 

 paired caecum, is plainly extremely different from the huge and 

 extremely definite colic loop, consisting of a closely applied 

 proximal and distal limb of very wide calibre, held together by a 

 very narrow expanse of the primitive mesentery, which forms, 

 perhaps, the most characteristic feature of the gut-pattern of the 

 Tapirs, Horses, and Rhinoceros (Mitchell, 1905, figs. 23-25, C.L., 

 and text-fig. 20, infra). As it happened, I found no definite 

 structure comparable with the loop figured by Beddard in 

 H. capensis or in B. dorsalis. If any comparison with the colic 

 loop of Perissodactyles were to be made, on the assumption 

 that the unpaired cfecum of Hyrax is identical with the caecum 

 of Perissodactyles, the analogue would be the whole expanse of 

 the gut from the unpaired caecum to the point where the recurrent 

 limb approaches the duodenum. 



To sum up. If the accessory caecum were absent, anatomists 

 would have found no difficulty in identifying the paired caeca of • 

 Hyracoids with the normal mammalian caecum, a structure 

 which, although usually unpaired, frequently shows vestiges of a 

 primitively paired condition, and less frequently is actually 



