RODENTIA. 



387 



the former to the right of its base, opening on 

 the constriction itself, so that aliments can 

 pass immediately into the second compart- 

 ment by the assistance of a fold, which is pro- 

 longed from the cardia into this cavity ; and the 

 pyioric portion may be distinguished, which 

 is more muscular than the rest, and ter- 

 minates in the intestine by a slightly pro- 

 minent pylorus. 



The Cape mole (Bathiergus, Iliger) like- 

 wise conforms to the preceding type of struc- 

 ture ; the left compartment of the stomach is 

 of enormous size, elongated and pierced at its 

 base by the cardiac orifice ; the left com- 

 partment is of smaller dimensions, of a glo- 

 bular form, and separated from the preceding, 

 both by an external constriction and an in- 

 ternal fold of the mucous membrane. There 

 are, moreover, two additional folds nearer to 

 the pylorus, which seem to form a third 

 compartment. The orycteres of the Downs 

 (Bathiergus maritimus} has its stomach slightly 

 different ; its position is more longitudinal, so 

 that the left compartment is anterior, and the 

 right posterior ; the pyioric portion short, 

 cylindrical, and directed forwards. 



In the beaver (Castor) the stomach is 

 transverse and elongated in that direction, 

 the right portion being larger than that which 

 is situated to the left of the cardia ; the 

 oesophagus is inserted into the first third of 

 its anterior margin by a narrow opening, sur- 

 rounded with pointed processes, which are 

 analogous to the fringes formed by the epi- 

 dermis in many other Rodents. At the point 

 where it terminates around the opening of 

 the first compartment of the stomach into the 

 second, numerous largely developed culs-de- 

 sac are distinguishable, which project more or 

 less beyond the cardia in different individuals. 

 On the right of this orifice commences the 

 pyioric portion, the termination of which is 

 indicated by an external constriction, and by 

 an internal thickened ring. The pylorus 

 is approximated very closely to the cardiac 

 orifice. This pyioric portion, which is more 

 muscular than the rest, is sometimes dilated 

 into a distinct pouch, separated by a con- 

 striction from the pyioric cul-de-sac. The 

 internal membrane presents every where the 

 same appearance, except that in the pyioric 

 portion it appears to be more smooth, and its 

 folds take a different direction. On the right 

 of the cardia there is a very thick fold, sepa- 

 rating the left from the right compartment. 



In the rabbit and the hare (Lepus, Lin.) 

 the stomach is very much elongated, par- 

 ticularly in that portion which is situated 

 to the right of the cardiac orifice. This 

 latter portion forms a bulb, the muscular wall 

 of which is thicker than elsewhere, especially 

 in the vicinity of the pylorus, where it is 

 swollen into a muscular ring. In the other 

 parts of the stomach the existence of this 

 layer is scarcely perceptible. 



In the lagoinys (Cuv.) we have again the 

 common type of structure, as also in the 

 agoutis and the pacas. 



In the pteromys (F. Cuv.) the stomach is 



situated more transversely, and the two culs- 

 de-sac are more distinct ; the right compart- 

 ment is the largest, and gives off at an an^le 

 a short conical pyioric portion. 



In the sciuropteres (F. Cuv.) the stomach 

 is round, deep from before to behind, and 

 having the bottom of the cardiac culs-de-sac 

 formed into a little pouch, and extending 

 slightly beyond the cardia ; the pyioric portion 

 is conical, very muscular, and lined internally 

 with a yellowish mucous membrane, whilst 

 the lining membane of the rest of the stomach 

 is white and arranged in folds, which form 

 arches parallel to the curvatures of the viscus. 

 There are two other folds running longi- 

 tudinally on the right and on the left of the 

 cardia, but which probably do not exist when 

 the stomach is distended : these would seem 

 to indicate traces of a division of the cavity 

 into three pouches. 



In the dormice (Myoxus, Gm.) the stomach 

 differs in shape in accordance with the appe- 

 tites of the different species. In the common 

 dormouse (Mus Glis, Lin.) it is conical, with 

 a small pyioric portion directed forwards ; its 

 membranes are thick and muscular, approxi- 

 mating the type of a carnivorous stomach. 

 InMyoxusNitela,on the contrary, it is globular, 

 and consists of a single sac ; the crypts, the 

 orifices of which open into the cavity of the 

 stomach, form a thick disc in the vicinity of 

 the eardia : these crypts are evidently small 

 culs-de-sac, formed by the mucous membrane 

 and the cellular layer beneath it, which here 

 appear folded upon themselves in irregular 

 festoons,, when a section of this glandular disc 

 is examined. The ligneous substances upon 

 which the beavers feed have rendered neces- 

 sary this superabundance of the secretions 

 furnished by this gland. A constriction se- 

 parates the pyioric portion from the re- 

 mainder of the straight part of the stomach. 

 The pylorus consists of a prominent ring 

 projecting into the intestine, 



In the family of the porcupines (Hystrix, 

 Lin.) we have another example of the dif- 

 ferences which the stomach may present in 

 different genera. In the cuendu (Synetheres, 

 F. Cuv.) this viscus resembles that of the 

 orycteres of the Downs, above described ; it is 

 elongated, longitudinal, with one compart- 

 ment anterior and the other posterior ; the 

 oesophagus is inserted into the right side ; the 

 cardia is placed far back, and approximated 

 to the pylorus ; the pyioric portion is short, 

 cylindrical, and directed forwards, terminating 

 by a ring, which projects into the intestine. 

 In the European porcupine (Hystrix cristafa, 

 Lin.) the stomach is globular, forming from 

 before to behind a deep and wide bag. 



Intestinal canaL The tract of the small 

 intestines offers nothing remarkable in the 

 Rodentia ; its walls are very thin, and its 

 diameter pretty even throughout. On coming 

 to the large intestinrs, the most striking fea- 

 ture is the enormous size of the caecum, 

 which, in many genera, itself fills up a 

 great proportion of the abdominal cavity. 

 There are, moreover, many interesting modi- 

 c c 2 



