and its parts, as compared with the body, in a few species of the different families of Marsupialia :

4

8

5

0 14

4

4

0

9

0

0

63

1

986

11132

287

24 10

845

11

010960291

21019722

18

8

11

24

0

0

32

25

11

14

223

ft. inch. ft. inch.

§ 226. Alimentary canal of Rodentia.-In relation to the de

317

gree of comminution of the food and in continuation of the character of the fauces the œsophagus is narrow in all Rodents and is usually continued a short way into the abdomen before opening into the stomach. The position of the cardia is at or near to the middle of the upper curvature (fig. 317, f, Rat, fig. 318, f, g, Vole) as in Marsupials, and the modifications of the alimentary canal in relation to the nature of the food are, also, manifested chiefly in the cæcum. The left end of the stomach commonly projects beyond the pylorus, fig. 317, d, fig. 318, b and it is not unusual to find both blind sacs' marked off by transverse constrictions from the mid-part of the cavity, fig. 317, b. The œsophageal epithelium is usually continued upon the inner surface of the cardiac compartment, ib. a. In the Porcupine, which shows well this tripartite type of stomach,

the pyloric aperture is much larger than the cardiac one and is bounded toward the left side by a valvular ridge.

In the Squirrels (Sciurus) the stomach is of a pyriform or oval shape, quickly contracting to a conical or cylindrical portion, which is bent upon the small curve and terminates in the pylorus. The cardiac compartment, which projects far to left beyond the œsophagus, is lined with a thick epidermis, which forms two oval lips, as it is prolonged around the opening into the second compartment, the lining membrane of which is gastro

mucous.

In the Hamsters (Cricetus) the stomach is divided into two pouches, separated by a deep constriction; the left pouch is cylindrical, the right globular. The cardiac orifice is situated in the constriction, so that food can pass at once into the pyloric compartment and be antiperistaltically moved and stored in the

cardiac division.

In the Rat (Mus decumanus) the abdominal part of the gullet, fig. 317, f, is 1 inches long, and carries forward a fold of peritoneum. The cardiac compartment, ib. a, has thin coats and is lined by an epithelium which usually gives it a whiter colour than the rest of the organ. At the midpart, ib. b, there is a tendinous

patch from which muscular fibres radiate, as in the bird's stomach: the muscular coats of the pyloric division, d, are thicker, as is also the gastro-vascular lining membrane.

In the Water-vole (Arvicola amphibius) the cardiac and middle compartments form one elongated cavity, fig. 318, a, f, separated by a constriction from the pyloric portion, b. This swells out in two directions, above into a small sacculus, e, the coats of which are thin, like those of f, and below into the true digestive pyloric part, with a thicker muscular tunic and gastro-vascular lining membrane.

The epithelial lining of a, f, terminates by a

fringed margin. The Lemmings have a similar type of stomach, complicated with a slight subdivision, fig. 319, c, of the right compartment, near the pylorus, where the thicker glandular lining graduates into the thin smooth mucous membrane of the suprapyloric sac, e. From the cardiac orifice a pair of ridges curve toward the pyloric division, defining a groove or canal, f, analogous to that which will be shown in the Ruminants; the border of the epithelium of the cardiac half is well-defined and sometimes fringed. The gastric tubes of the compartment, b, are so complex as to give the character of a gland to the lining membrane.

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, surrounded with pointed processes, which are analogous to the fringes formed by the epithelium in many other Rodents. On the right of the œsophagus, at the lesser curvature of the stomach, is a gastric gland composed of numerous branched follicles, the blind ends of which, when exposed by removal of the muscular coat, give the gland a lobulated surface: the orifices of the glands are arranged on slight ridges in three longitudinal rows on a flat tract of the inner surface. On the right of these orifices commences the pyloric portion, the termination of which is indicated by an external constriction, and by an internal thickened ring: the pylorus is approximated to the cardiac orifice. This pyloric portion, which is more muscular than the rest, is sometimes dilated into a distinct pouch, separated by a constriction from the pyloric cul-de-sac. The internal membrane presents everywhere the same appearance, except that in the pyloric 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, separating the left from the right compartment. In the Dormouse (Myorus glis) and Muscardine (M. avellanarius) similar follicular glands are aggregated round a dilated termination of the oesophagus, or cardiac commencement of the stomach, like the proventriculus of birds.' We have here a repetition of the structure noted in the Wombat.

In the Cape Mole (Bathyergus) the abdominal œsophagus is an inch in length and terminates midway between the two ends of the stomach. The right compartment is of enormous size, elongated and pierced at its base by the cardiac orifice; the left 1 xx. vol. i. p. 181, No. 590 a.

compartment is of smaller dimensions, of a globular form, and separated from the preceding, both by an external constriction and an internal fold of the mucous membrane. There are, moreover, two additional folds nearer to the pylorus, which seem to form a third compartment. The Oryctere (Orycterus) has its stomach slightly different: its position is more longitudinal, so that the left compartment is anterior, and the right posterior; the pyloric portion is short, cylindrical, and directed forward.

In Capromys Fournieri the oesophagus, after a short course in the abdomen, terminates in a stomach six inches long, about 24 inches from the left end: a pouch of the same extent is continued from the right of the pylorus, which is situated 1 inches to the right of the cardia.

In the Coypu (Myopotamus) the stomach closely resembles that of Capromys, being of an oblong figure, both extremities having pretty nearly the same volume; the cardiac extremity projects three inches beyond the entrance of the narrow œsophagus, and the pyloric sacculus, a little more than two beyond the pyloric orifice. The stomach, measured in a straight line from end to end, is 7 inches; its greatest depth 44 inches.

In the Agouti (Dasyprocta agouti), with a stomach 5 inches long, the constriction dividing it into cardiac and pyloric portions is deep the latter bulges out on each side the pylorus so as to make the duodenum commence from a central depression. The Paca (Coelogenys) shows the same structure. In an Acouchi the gastric constriction was not present or had relaxed. In the Capybara the abdominal œsophagus is two inches in extent: the greater curvature of the stomach is sometimes found puckered into sacculi by contraction of a band of longitudinal fibres.

In the Rabbit and Hare (Lepus, Lin.) the stomach is roundish, bent in a quick curve, with the oesophagus entering nearer the left or great end than the pyloric end: the left end adheres to part of the abdominal œsophagus: it is usually found partially constricted into two compartments, the pyloric being the thickest and most muscular. The sides of this division have a well-marked tendinous patch.

The intestinal canal usually, in Rodents, begins by a well-marked dilatation, and the whole duodenum is more continuously and loosely suspended than in most higher Mammals. In the Dormice (Myoxus) which hybernate like the bear, there is no cæcum. In the common Mouse and Rat (Mus, fig. 317) the cæcum, k, l, is short, wide, and bent; the colon, p, reduced to the calibre of the ileum, leaves the cæcum, like the duodenum quitting the stomach. The

fæces begin to be divided in the colon, by constrictions of the gut, as in the figure the rectum runs some way along the base of the tail before terminating. The small intestines are five times the length of the body, the large intestines once that length. In

320

the Mole-rat (Bathyergus) the cæcum makes a close spiral turn, and its inner membrane is augmented by many transverse folds. The cæcum is of greater length in the Sciurida: in the common Squirrel it is curved, fig. 320, c, and divided from the colon, e, by a constriction close to the termination of the ileum. The colon is wider at its commencement than in the Rats, and the whole intestinal canal is longer. In Sciurus griseus the small intestines are seven times, the large intestines twice, the length of the body; the cæcum is half that length. In the Hamster the colon describes two direct and two reflected spiral coils at its commencement, decreasing in calibre, and then proceeds, of nearly the same diameter as the ileum, to terminate in the rectum. In the Marmots (Arctomys) the duodenum passes loosely down the right side until its attachment, by a mesentery from its concavity, to the first bend of the colon, behind which it winds to the left; and after an attachment to the descending colon by serous layers from its convexity, becomes jejunum. The long and large cæcum has a mesentery; its inner surface is multiplied by circular folds, indicated outwardly by constrictions which led Hunter to compare it to a quilted petticoat.' The indication of the low grade or affinities yielded by the termination of the intestines, is thus noted in the present Lissencephalan:-The rectum cannot be said to terminate at the verge of the anus; but about three-quarters of an inch higher up, that lower part seems common to the anus and to a glandular apparatus whose ducts open into it. It is something like the common vagina to the bladder and uterus in fowls.'3 In Capromys the ileum CCXXXVI. vol. ii. p. 242.

Cæcum of the Squirrel. CXXII.

1 cxx". xxm. p. 134, pl. xv.

Ib. p. 243.

2