202 DR. p. CHALMERS MITCHELL ON THE 



formed was broken up into a numerous set of closely disposed 

 minor loops. The distal or recurrent limb was straight for the 

 greater part of its length, and as it approached the dorsal line, 

 entered the expanded hind-gut between a pair of cfeca relatively 

 longer than in the adult and disposed on the light and left sides 

 of the gut. The hind-gut distad of the pendant loop had a 

 distinct colic loop, attached to the duodenal region by a ligament, 

 removed before the figure was drawn. 



The patterns of the intestinal tracts of the Tubulidentata,. 

 Pholidota, and Xenarthra afibi'd no evidence in favour of the 

 existence of a super-order " Edentata." Such resemblances a& 

 they present are best explained as a common inheritance from 

 the primitive type, and so afford no evidence of affinity. In the 

 Xenarthra, the most characteristic features are the existence of 

 paired cseca, which seem to be more conspicuous in the young 

 than in the adult, and the tendency to a great elongation of 

 the loop formed by Meckel's tract and the proximal portion of the 

 hind-gut, a tendency which is better marked in some of the 

 examples described in my former memoir, than in the young 

 Armadillo figured here. The hind-gut varies considerably both 

 in the different groups and even individually. The distal limb 

 of the pendant loop always approaches the duodenum closely, and 

 distad of this the hind-gut may pass nearly straight back to the 

 rectum, may form a shallow, or a well-marked and complex loop. 

 In both Marsupials and Edentates, the hind-gut appears to be 

 still in a variable or almost experimental stage. 



Order Hyracoidea. Dendroliyrax dorsalis (text-fig. 12). 



The pattern of the intestinal tract of the Hyracoidea is the 

 most remarkable to be found amongst mammals, and deserves 

 special attention, because of the difficulty that has been found in 

 assigning its due place to the Order amongst the mammalian 

 Orders. I have already described and figured (Mitchell, 1905,^ 

 p. 461) the intestinal tract of Ilyrax capensis; since then I have 

 been able to examine an adult example of Dendrohyrax dorsalis 

 and another very young example of H. capensis, and to compare 

 my own observations and interpretations with those of Dr. Beddard 

 (Beddard, 1908 and 1909). The pattern of the tract of the Tree- 

 hyrax (text-fig. 12), when the secondary connections have been 

 severed and the tract laid out according to the method I pursue, 

 corresponds in all essential respects with that of other Hyra- 

 coids. As Owen long ago (Owen, 1832) correctly stated, the 

 whole tract, from the duodenum to the distal extremity of the 

 rectum, is suspended by the primitive mesentery from the dorsal 

 wall of the body-cavity. In Dendrohyrax I found interruption 

 in the proximal part of the mesocolon (extending from the point 

 marked X in the text-figure towards the recurrent limb of the 

 pendant loop), a gap that I did not notice in D. capensis. The 

 duodenal region is a distinct loop, well separated from Meckel's 

 tract. 



