224 



DR. p. CHALMERS MITCHELL ON THE 



occurs frequently in Rodents and is extremely rare in other 

 groups, so that it may be designated as a Rodent peculiarity, 

 affects the caecum. 



The colic loops may be pressed against the mesentery of 

 Meckel's tract in such a fashion that their own primitive mesentery 

 may be partly obliterated and replaced, either by the mesentery 

 of "the tract, or by adventitious fibres. In Dijms (although in 

 this respect text-fig. 21 is somewhat simplified and diagrammatic) 



Text-figure 21. 



Intestinal tract of Dipus eegyptius. 



S. Cut end of tlie gut nearest to the stomach. R. Cut end of the gut nearest to 

 the rectum. C. Ca=!cum. C.L. 1, 2, 3. Colic loops. C.L. 1. Paracsecal loop. 

 C.L. 2 & 3. AnscB coli dextree. 



and in other forms with a relatively simple gut, it is still possible 

 to dissect away the colic loops and to unfold them to show their 

 primitive pattern with a minimum of cutting. In other forms, 

 especially those in which the loops are long, the adherence 

 between them and the tract is so elaborate as to recall the 

 condition in Artiodactyles, and the gut cannot be laid out to 

 show its primitive pattern without extensive destruction of 

 mesentery, blood-vessels, and secondary attachments. I am 



