484 DR. P. CHALMEES MITCHELL ON THE 



and shows signs of spiral twisting. The hind-gut is composed of two rather irregular, 

 narrow colic loops, and the rectum is relatively long. 



Group Bathyergoidea. 

 I have not been able to examine any example of this group. 



Group Htstricoidea. 



Family HystricidjE. Ilystrix cristata, Sphingurus prehensilis, Atherura 

 africana. 



In the Porcupine there is a distinct duodenal loop. Meckel's tract is long and 

 composed of numerous, rather short, irregular loops, disposed in the usual fashion 

 round the edge of an elongated, hemispherical expanse of mesentery with a very short, 

 straight, terminal portion. The caecum is very long and rather narrow. The proximal 

 portion of the hind-gut is expanded and forms a kind of accessory caecum. The colic 

 portion of the hind-gut is composed of two long, distinct, but rather irregular groups, 

 and the rectum is relatively short and straight. The anterior mesenteric vein is short 

 and very wide, and receives a number of radiating veins from the loops of Meckel's 

 tract and a large csecal vein, as well as two veins from the colic loops, whilst in the 

 usual fashion it is joined by the posterior mesenteric vein from the rectum. 



In the Tree-Porcupine (Sphingurus prehensilis) the pattern is closely similar. The 

 minor loops of Meckel's tract are rather less numerous ; the caecum is very long and 

 capacious, but terminates in a long, slender, finger-like process, which may be described 

 almost as a vermiform appendix. The hind-gut has precisely the disposition of that 

 region in the Common Porcupine, and the arrangement of the mesenteric veins is 

 similar. 



In the Brush-tailed Porcupine (Atherura africana) the duodenum is less distinct ; 

 Meckel's tract is relatively considerably longer, with more numerous minor loops. The 

 caecum is large and tapers more gradually to a point. The hind-gut has the same pair 

 of colic loops and a straight rectum. The mesenteric veins are practically identical in 

 their disposition. 



Family Erethizontid^e. 

 I have not examined any members of this family. 



Family Caviid2E. Cavia porcellus (fig. 28), Hydroclmrus capybara (fig. 29, 

 p. 486), Dolichotis patachonica. 



In the Guinea-pig (Cavia porcellus) there is a distinct duodenal loop. Meckel's 

 tract is relatively long and is composed of a number of long, irregularly arranged, and 

 contorted minor loops at the periphery of an oval expanse of mesentery. The terminal 



