184: DR. P. CHALMERS MITCHELL ON THE 



is a reproduction of a photograph kindly taken for me by my 

 colleague, Mr. D. Seth- Smith, and shows the intestinal tract of 

 the Elephant-Seal prepared in this way. It will be seen at 

 once how closely it corresponds with the simplified diagrammatic 

 drawings of dissections which are the material of the other 

 text-figures in my former memoir and in this communication. 



In most cases, however, and especially where the alimentary 

 canal is relatively long and thin-walled, or where difterent 

 portions differ notably in calibre, regions of the tract belonging 

 to one morphological part are held in close adherence to regions 

 belonging to another morphological part. Some of these adhesions 

 are individual : such are more common in old animals and in 

 animals loaded with fat or plainly diseased. Others are permanent 

 structures, invariably present in the members of the species in 

 which they occur — as, for example, the connections between 

 the colon and the duodenum which have been named the 

 cavo-duodenal and the colico-duodenal ligaments, or the attach- 

 ment of the omentum to the colon. Sometimes, moreover, 

 blood-vessels belonging to one region of the gut may traverse 

 the adhering folds of mesentery and supply morphologically 

 remote regions of the gut. 



In extreine cases the secondary adhesions may be stronger 

 than the primitive mesentery, and large portions of the latter 

 may have disappeared. Sometimes, therefore, the pattern can be 

 ■displayed only after tedious dissection and the cutting of many 

 structures not easy to distinguish from the primitive mesentery ; 

 but when the process has been accomplished, the pattern of gut 

 and primitive mesentery is revealed. 



The mode in which the intestinal tract and its mesentery 

 are folded in the body-cavity, and the secondary adhesions, 

 pathological or permanent, that are formed, are of gi-eat surgical 

 importance ; and many anatomists, for the most part cited in 

 my former memoir (Mitchell, 1905), have paid attention to them. 

 Their bias towards secondary phenomena, with consequent over- 

 looking of the relations of the gut-patterns that I have tried to 

 work out, has made it impossible to derive a coherent picture of 

 the morphology of the mammalian gut from their work. 



The literature of surgery gives us a clear idea as to how 

 secondary connections may be established when living membranes 

 are in juxtaposition, and it is a fair supposition that such 

 ^' accidental " structures may have become permanent features 

 ■of the anatomy where they were useful. The intestinal tract is 

 a muscular tube, constantly undergoing strong peristaltic waves 

 of contraction. Its contents, sometimes liquid, sometimes 

 strongly charged with gases, sometimes with solid hard lumps, 

 are seldom quiescent, but partly from the mere action of gravity, 

 and partly because of peristalsis, subject the wall and the 

 delicate suspensory apparatus of mesentery with the con- 

 tained blood-vessels and nerves to sudden and varying strains. 

 These strains are of relatively little importance when the gut 



