Pure saliva obtained from the parotids and submaxillaries of a dog, and from the parotids of a horse, is incompetent to effect the saccharine transformation of starch: but the secretion of the mucous and subsidiary glands of the mouth reacts upon either starch or sugar in the way of producing lactic acid.

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§ 225. Alimentary canal, Lyencephala. In the Ornithorhynchus the œsophagus becomes slightly dilated near the diaphragm, extends a little way into the abdomen, and expands into a moderate-sized membranous stomach, fig. 308, t, which is chiefly remarkable for the close approximation of the cardiac and pyloric orifices. The intestinal canal is moderately wide, five feet three inches and a half in length, and provided, at a distance of four feet three inches from the pylorus, with a small and slender cæcum, ib. w. The small intestines are chiefly remarkable for the extent of the mucous coat, which is disposed in numerous folds or valvulæ conniventes: these are transverse at the beginning of the duodenum, but are placed more or less obliquely in the rest of the small intestine; they are about two lines broad, are close together in the duodenum, but diminish in breadth and number as they approach the cæcum coli. There are about fifteen longitudinal folds in the first half of the colon; the remainder of the intestine has a smooth inner surface. There is no valvula coli. The rectum, ib. z, terminates at the anterior and dorsal part of the vestibular

Thoracic and abdominal viscera, Ornithorhynchus, compartment of the cloaca.

LXXXI'.

As the food undergoes less comminution in the mouth of the Echidna than in that of the Ornithorhynchus, the pharynx and oesophagus are wider, and a

dense epithelium lines the inner surface of the latter tube: it is continued over the capacious stomach to the pylorus, near which orifice it is developed into numerous horny and sharp papillæ. The subjacent mucous membrane is smooth; the tunics of the stomach are thin, to near the pylorus, where the muscular coat assumes something of the gizzard-character, and the inner coat forms a prominent protuberance in the duodenum. The intestinal canal of the Echidna is seven times the length of the body; the mucous membrane is not raised into valvular folds; a small vermiform and glandular cæcum divides the small from the large intestines; the rectum terminates as in the Ornithorhynchus.

The various modes of locomotion, resulting from the different modifications of the osseous and muscular systems observable in the several families of Marsupialia, relate to the acquisition of as various kinds of alimentary substances, which necessarily require for their assimilation as many adaptations of the digestive organs. Food-means of obtaining it-instruments for preparing and mechanically dividing it-cavities, canals, and glands for chemically reducing and animalising it-form a closely connected chain of relationships and interdependencies. The preparatory instruments have been described in previous sections. In all Marsupials the oesophagus in passing through the chest recedes from the spine as it approaches the diaphragm, and is loosely connected with the bodies of the dorsal vertebræ by a broad duplicature of the posterior mediastinum. In the Phalangers the œsophagus terminates in the stomach almost as soon as it has pierced the diaphragm; in the Opossums it is continued some way into the abdomen; in the Didelphys virginiana, for example, for the extent of an inch and a half; in Did. brachyura, for half an inch. In the Kangaroos the abdominal portion of the œsophagus is of still greater extent; I have observed it five inches long in a male Macropus major.

The inner surface of the œsophagus is generally smooth, or disposed in fine longitudinal plaits; but in the Virginian Opossum the terminal part of the oesophagus presents many transverse folds of the lining membrane analogous to, but relatively larger than, those in the Lion and other Felines. I have not met with a like structure in the Phalangers, nor in any other genus of Marsupials; what is more remarkable is that the transverse œsophageal rugæ are not developed in the carnivorous Dasyures or Phascogales, where analogy would lead one to expect them, rather than in the insectivorous Opossums.

The stomach presents three leading modifications of structure

in the Marsupialia; it is either simple, as in the Zoophagous, Entomophagous, and Carpophagous tribes; or is provided with a cardiac glandular apparatus, as in the Koala and Wombat; or is complicated by sacculi, as in the Poephagans.

It might have been expected that the stomach would have exhibited some modifications in the development of the left or cardiac extremity corresponding with the differences of food and dentition observable in the large proportion of the Marsupial order, in which this viscus presents its simple condition; but this is not the case: the form of the stomach is essentially the same in the carnivorous Dasyure, the insectivorous Bandicoot, and the leaf-eating Phalangers. It presents a full, round, ovate, or subtriangular figure, with the right extremity projecting beyond and below the pylorus; the longitudinal diameter seldom exceeds the vertical or transverse by more than one-third; often, as in Phas

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cogale and Dasyurus viverrinus, by only one-fourth of its own extent; and the oesophagus enters at the middle of the lesser curvature, or sometimes nearer the pylorus, but always leaves a large hemispherical cul-de-sac on the left side. Daubenton' has given illustrations of this characteristic form of the stomach in different species of Didelphys; it is here figured as it exists in the Phascogale, fig. 309. The stomach is relatively much more capacious in the carnivorous Marsupials than in the carnivorous Placentals. Some slight modifications occur in the disposition of the lining membrane; in the Phascogale a series of very thick rugæ radiate from the middle of the upper part of the cæcal end of the stomach, some of which were continued along the lesser curvature to the pylorus. In the Perameles nasuta the internal surface of the left cul-de-sac is smooth; the right half of the stomach has rugæ, running chiefly in a longitudinal direction, and particularly numerous towards the pylorus.

' cxxII", tom. x, pl. 48, fig. 1.

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The stomach in the Wombat and Koala does not materially differ in external figure from that of the above-cited Marsupials; the œsophagus terminates nearly midway between the right and left extremities, but further from the pylorus in the Wombat than in the Koala. The conglomerate gastric gland is of a flattened ovate form, relatively larger in the Wombat than in the Koala, situated to the left of the cardiac orifice, at the lesser curvature of the stomach, fig. 310. The gastric gland has a similar position in the Beaver, but in this animal the excretory orifices of the gland are arranged in three longitudinal rows, while in the Wombat and Koala they are scattered irregularly; in the Wombat they are

about thirty in number, and the bottoms of the larger depressions are subdivided into smaller cells. In the partially contracted state the inner membrane of the stomach of the Wombat is disposed in longitudinal rugæ,

which gradually subside towards the pylorus; but when the stomach is distended these folds disappear, and the left extremity presents a full globular form.

The sacculated stomach of the Kangaroo, which offers the extreme modification of this organ in the Marsupial order, resembles the human colon both in its

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longitudinal extent, structure, and disposition in the abdomen. In a full-grown female Kangaroo (Macropus major) I found the abdominal oesophagus, fig. 311, a, four inches long, and terminating at six inches distance from the left extremity of the stomach: this was folded forward and to the right in front of the œsophagus; from the basis of the left cul-de-sac the stomach continued to expand, and descended into the left lumbar and

iliac regions, whence it stretched upward and to the right side obliquely across the abdomen, to the right hypochondrium, where it became contracted and finally bent downward and backward to terminate in the duodenum. The whole length of the stomach, following its curvatures, was three feet six inches, equalling that of the animal itself from the muzzle to the vent.

The cavity may be regarded as consisting of a left, a middle, and a right or pyloric division. The left extremity of the stomach is bifid, and terminates in two round cul-de-sacs. The sacculi of the stomach are produced, like those of the colon, by three narrow longitudinal bands of muscular fibres, which gradually disappear, together with the sacculi at the pyloric division. One of the longitudinal bands runs along the greater curvature, at the line of attachment of the gastro-colic omentum; the others commence at the base of the left terminal pouches, and run, one along the anterior, the other along the posterior side of the stomach the interspace, between these bands, forming the lesser curvature of the stomach, is not sacculated. The largest of the two terminal sacculi, d, fig. 310, is lined with an insulated patch of vascular mucous membrane, which is continued for the extent of five inches into the cardiac cavity; the thick epithelium is continued from the oesophagus in one direction into the nearest and smallest sacculus, c, and extends in a sharp-pointed form for a considerable distance in the opposite direction into a series of sacculi in the middle compartment of the stomach, ib. e: this epithelium is quite smooth. The vascular mucous surface recommences by a point at the great curvature, near the beginning of the middle compartment, and gradually expands until it forms the lining of the whole inner surface of the right half of the stomach. Three rows of clusters of mucous follicles, ib. g, J, are developed in the mucous membrane of the pyloric half of the middle compartment; they are placed parallel with the longitudinal muscular bands: about fifteen patches are situated along the greater curvature, and there are nine in each of the anterior and posterior rows. These glandular patches disappear altogether in the pyloric compartment of the stomach, where the lining membrane is thickened, and finely corrugated; but immediately beyond the pylorus there is a circular mucous gland three-fourths of an inch broad: the non-sacculated pyloric division of the stomach was five inches in length.

In the smaller species of Kangaroo the stomach is less complicated than in the Macropus major; the number of sacculi is fewer in Macropus parryi, e. g., the third longitudinal band at the great curvature of the stomach is almost obsolete: in the