220 



DR. P. CHALMERS MITCHELL ON THE 



been selected as the apex would place the mesenteiy on the 

 wrong side of the gut. The supposed distinction in type does 

 not exist. 



I do not doubt but that an intensive study of these ruminant 

 coils may lead to very interesting results. It is important to 

 realize, however, that a naive comjjarison and description of such 

 couiplex structures may be extreujely misleading. 



Distad of the colic spiral the recurrent limb of the pendant 

 loop undergoes a further complication before it reaches the 

 dorsal middle iine. The outgoing limb of the spiral, still with 

 its mesentery adherent to the mesentery of Meckel's tract, 

 pursues a circular course, following the line of the secondary 

 coils of Meckel's tract and lying between this and the spiral 

 itself until it reaches the duodenal region, where its suspension 

 is usually reinforced by a colico-duodenal ligament, and then 

 bends round to form the rectum, which passes backwards towards 

 the anus suspended in the usual fashion by its own primitive 

 mesentery. The adherence of this special coil to the mesentery 

 of Meckel's tract is so close, that 1 have never been able to 

 dissect it off with any portion of its own mesentery, and I 

 suspect that this mesentery has disappeared. In the diagrams 

 that I have given of Traguloidea, Tylopoda, and Pecora (Mitchell, 

 1905, figs. 19-22), this portion of the gut is marked S.F., 

 supra-meckelian fold, and is displayed as dissected off and free 

 from mesentery. This region appears to be simplest in the 

 Ti-aguloidea and the Tylopoda, but in an example of the White- 

 tailed Gnvi {ConnochcBtes gnu) I was surprised by finding it reduced 

 to a single quite narrow loop. In the Giraffe it is very com- 

 plicated, forming, instead of a wavy line round Meckel's tract, a 

 set of irregular loops in the space between the tract and the 

 spiral coil, rather like a similar series that Dr. Lonnberg has 

 figured in the case of a foetal Elk (Lonnberg, 1907, fig. 4)*. In 

 some of the deer, sheep, and goats that I have examined, the 

 general course of this loop is a sweeping curve concentric with 

 the cvirve of the minor loops of Meckel's tract, but at the distal 

 end, just before bending over to form the rectum, it gives rise 

 to a quite definite, straight, and rather narrow loop, stretching 

 across towards the spiral coil and sometimes even crossing a 

 portion of the coil. 



I am reluctant to suggest homologies between the minor loops 

 found on the veiy peculiar hind-gut of this group of Artio- 

 dactyles and the minor loops found in the hind -gut of other 

 groups, as it seems to be plain that we should have first to ti'ace 

 such loops down to their form in the ancestral Artiodactyle, 

 Rodent, and Primate, and so forth, before instituting any valid 

 comparison betvveen their appearances in the higher members of 

 these difi;erent gi-oups. In the very general sense, however, that 

 the distal or dorsal extremity of the recurrent loop corresponds 

 with the transverse colon, and a specialized outgrowth to the 

 right of this may be na.med an ansa dextra, a specialized out- 



