EHIZOMYS. 319 



and the mucous membrane is very rough, being thrown into numerous fine tortuous 

 rugae, which are arranged more or less parallel to the long axis of the cul de sac, 

 and which become longer and better defined in parallel series, below the cardiac orifice. 

 This structure exactly resembles that which A. M. -Edwards has described and 

 figured in Siphneus. 



In B. bacl'ms, on the other hand, although the eul de sac is absent, there is a 

 decided, though partial, thickening of the walls to the left of the cardiac orifice, in 

 the position in which the fringe occurs in H. pruinosus ; but the inner surface, with 

 the exception of a small area about a quarter of an inch square on the anterior wall 

 of the cardiac end of the viscus, is quite smooth. This Kmited patch is covered with 

 deep irregular rugse. 



The middle division, or general cavity of the stomach of M. pruinosus, is 

 continuous with the swelling to the right of the oesophagus, and both are 

 glandular, but the walls are very thia and continuous mth those of the pre- 

 pyloric sack which is only separated from this cavity by a slight constriction. 

 On the bulging to the right of the oesophagus, there is a well-defined glandular 

 patch, afiined to that which occurs in the same locality in the stomach of the 

 beaver. The pylorus is well indicated in both species by a decided tliickening 

 of the walls. 



The first inch of the duodenum is covered with minute, leaf -shaped villi, and is 

 studded over vtdth soHtary vesicular glands. As the small intestine approaches the 

 caecum, it contracts to half its general capacity. In an animal, 12'25 inches in 

 length from the muzzle to the vent, the small intestine was only 30 inches in length, 

 whUe the great gut attained to a length of 42'25 inches ; and in a female, measuring 

 11"50 inches long, the small intestine was 27'50 inches and the large 42"50 inches in 

 length. In R. badins, however, there is not the same disproportion between the 

 two sections of the digestive tube, because in a male of that species, 7 inches from 

 muzzle to root of tail, the small intestine was 23'50 inches and the large intestine 

 only 25 inches long. In the two foregoing examples of R. pruinosus, the caecum, 

 in the first, was 6-25 inches and in the latter 6 inches long, whilst in R. bad'ms it 

 was only 2 "10 inches in length. 



In both species, the structure of the caecum is nearly the same, and it conforms 

 to the characters displayed in Siphneus, and which recalls to mind the caecum of the 

 Leporidce. The orifice of the small intestine is either an oval or rounded opening 

 with a thickened rim or lip; and in R. pruinosus it is partially shut oft' from 

 the caecum by an arched fold of mucous membrane which arises from both sides 

 of the wall of the large intestine, some way below the opening. The inner 

 surface of the sack is marked by a broad fold describing from seven to eight spu-al 

 turns at regular intervals, the presence of the fold being indicated externally by 

 spiral contractions of the wall of the caecum. In R. badius the fold describes only 

 four spiral turns. It commences on one side of the opening from the small 

 intestine and arches closely over it, acting apparently as a kind of valve. Two folds 

 arise close to each other from the lower margin of the orifice and pass downwards 



