In the family of the porcupines (Hystri.r, 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 pyloric portion is short, cylindrical, and directed forwards, terminating by a ring, which projects into the intestine. In the European porcupine (Hystrix cristata, Lin.) the stomach is globular, forming from before to behind a deep and wide bag.
Intestinal eanal.—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 intestines, the most striking fee ture is the enormous size of the cmcum, which, in many genera, itself fills up a great proportion of the abdominal cavity. There are, moreover, many interesting modi fications to be noticed, both in the construc tion of the mean) and of the commencement of the colon, which generally presents the same appearance as the cmcum itself for a short distance from its commencement.
The greater or less development of the ate= is in relation to the nature of the food appropriate to each individual. In one genus only, namely, the dormouse (Myo.rus), it is altogether wanting ; those Rodents that live upon grass and herbs have it most remark ably developed ; and in the hare it has been calculated that the capacity of the CTCUM is ten times as great as that of the stomach itself. In the granivorous genera its size is likewise very considerable ; so that, in the hamsters, lemmings, Guinea-pigs, and allied genera it has been estimated to be four times larger than the stomach.
Another remarkable peculiarity may be observed in the cmcurn of the Rodentia, namely, that it frequently- has its cavity divided into regularly arranged cells disposed in several rows, or else forming a single series. In other cases the cavity of the caecum is divided into compartments by a broad spiral membrane. In soine species again, as in the jerboa, &c., the interior of the cmcum is a simple cavity, without any division or internal complication. All these diversities of struc ture seem to be in relation with the different kinds of food devoured by these animals.
The proportionate length of the small in testine as compared with that of the large, is frequently the reverse of what holds good in carnivorous quadrupeds ; but the diameter of the latter, except in the immediate vicinity of the cmcum, is scarcely greater than that of the small intestine (fig. 273. 711, n).
The intestinal villi have the shape of leaf lets of fringed laminm, or sometimes of very fine filaments ; the entire inner surface of the small intestine is villous, whilst that of the large intestine is quite smooth.
valve, as is the case in the hares ; or, as in the. marmots, by circular foltls of its lining cesophagus ; a, b, d, compartments of the stomach ; e, pylorus ; g, h, i, small intestine; k, 1, -maim ; p, commencement of the colon; m, n, colon; allUS.
It is worthy of observation that in those species that have the cmcum most largely de veloped, that organ is furnished with very remarkable glandular appendages; this struc ture is met with in the genera Leptis and Lagomys.
In order to illustrate the above general description of the digestive organs of the order of quadrupeds under consideration, NA e shall select a few examples illustrative of the principal varieties which it presents in dif ferent genera.
In the squirrel (S'ciurns) the small intestine (fig. 272. a) is nearly of the same diameter throughout ; the cmcum (b, c, d) is of mo derate dimensions, of a conical shape, and destitute of any cells or partitions internally.
The colon (e) is for a short distance almost of the same diameter as the cmcum, but it soon diminishes in size, and throughout the rest of its extent is scarcely wider than the small intestine. Internally, it presents no septa or valvulm conniventes. The intestinal papillm form small lamellm, the borders of which are fringed with delicate filaments ; these papillm extend throughout the whole length of the small intestine, but towards its termination becomes smaller and less per ceptible.
In the rats, the alimentary canal would be nearly of the sarne calibre throughout, were it not for the interposition of the cream between the ileum and the colon. The crecum in this family of Rodents mther re sembles a second stomach (fig. 273. k,l) than a bowel ; it is capacious, short, and slightly curved upon itself, but without any constric tions, tapering gradually towards its blind ex tremity. The walls of the intestinal canal are throughout thin, delicate, and transparent ; but slight traces of a spiral valve are visible at the conunencement of the colon.