folds of the mucous membrane at the beginning of the colon, and not extending round the circumference of the gut but the boundary of the ileum is not defined by any ileo-colic valve nor by any appreciable alteration in the vascularity or other structure of the mucous membrane in the two divisions of the intestinal canal. The inner surface of the colon is smooth, finely reticulate, with a few very narrow transverse folds, from 1 inch to half an inch apart, subsiding for the most part before reaching the attached line of the gut; these folds are not obliterated when the canal is fully distended; they commence about 18 inches from the ileum, gradually become shorter and narrower, and disappear about a foot from the rectum. The longitudinal folds of the rectum extend to the margin of the anus, where a little dark pigment is developed under the epithelium. The soft epithelial-covered integument extends from the fore part of the anus to the vulva, which is distant about half an inch. The longitudinal muscular fasciculi of the rectum and rectal end of the cloaca are strongly marked, and are from one line to one line and a half in breadth. The specimen dissected' measured 4 feet 7 inches from the snout to the vent: the intestinal canal was 34 feet in length, the large intestines being but 4 feet of that

extent.

354

In the little two-toed Anteater the double cæcum reappears: 2 but each is relatively rather longer than in the six-banded Armadillo. In the two-toed Sloth (Cholapus) the oesophagus is lined by a dense epithelium disposed in longitudinal folds: it communicates with both the first and the second compartments of the cardiac division of the stomach, fig. 354. The first compartment is the largest, and is subdivided into a left and right portion; the left, b, terminating below in a short cæcal appendage, c: its inner surface is minutely villous and vascular. The right compartment of the paunch is partially subdivided into a larger left and a smaller right cavity, d, both of which are lined by a continuation of the thick epithelium of the oesophagus, the inner surface of 'vi". p. 121, pls. li, lii, and liii.

2There are two cæca, as in birds,' ccxxxvI. vol. ii. p. 181.

which is minutely wrinkled, but not villous: the thick epithelium terminates in a free, minutely jagged border. A groove or canal is continued from the cardia along the right side of the incomplete septum dividing the right compartment of the paunch, d, and curves downward to communicate by a moderately wide crescentic aperture with the second or middle division of the stomach, g. This division presents the ordinary form of a simple stomach, but in a reversed position, i.e. with the great curvature turned toward the diaphragm: it communicates with the right compartment of the cardiac division by the right extremity of the crescentic œsophageal aperture, and with the third or pyloric division of the stomach by the left extremity of the same canal: a fold formed by the lower end of the left wall of the oesophageal groove divides these two communications. In the character of its lining membrane the second division resembles the right compartment of the cardiac division, and should be regarded, physiologically, as a third subdivision of it. The third, or pyloric cavity, f, has also the form of the ordinary simple stomach, but with the great end next the pylorus; the smaller or left end swells out about half an inch to the left of the crescentic aperture by which both the second cavity and the œsophageal groove communicate with it. The thick epithelium is continued over the inner surface of the third cavity to the pylorus, increasing in thickness toward that part, and taking on a coarse villous character. The thick epithelium is absent from an oval patch at the great curvature, e, the surface of which is vascular and minutely villous; about half an inch to the left of the free epithelial border of the mucous patch, there is the apex of a gland, lodged in a circular fossa, 1 line in diameter, and closely resembling one of the 'fossulate papillæ' of the tongue.

The leading character of the stomach in Bruta is one tending to compensate for the poor masticating machinery in the mouth, indicated by Cuvier's name of the order. It is, of course, least conspicuous in the toothed families: but even in these the musculo-tendinous structures at the pyloric portion, and the thick epithelium continued over the inner surface of that part in the Phyllophagous species, significantly indicate a community of type under the mask of the most complex modifications of the digestive cavity. The great expanse and subdivision by broad and permanent folds of the cardiac cavity, in fig. 354, simulates the ruminant stomach: but the position of the vasculo-villous part of the lining membrane is similar to that of the more special glandular

GG 2

part in the Manis.' In all Sloths the duodenum is loosely suspended, and is continued without constriction of mesentery into the rest of the small intestines, which is disposed in many short convolutions, and enters a short and straight colon, without a cæcum. The anus is not distinct from the vulva.

§ 333. Alimentary canal of Cetacea.-The first peculiarity to be noted in this order is the small area of the gullet in the largest

355

species, especially in the great Whale-bone Whale (Balana mysticetus): its lining membrane is here disposed in longitudinal folds which close the area of the tube in the contracted state: they are coated by a thick irregularly rugous epithelium, and are connected with the strong muscular coat by a deep layer of elastic cellular substance. The stomach is complex, divided into several cavities, in all true Cetacea. In the Porpoise (Phocana communis), fig. 355, the first cavity is continued in the same line with the œsophagus, having the same structure, and not being divided from it by any sensible constriction; its commencement is indicated by the orifice leading into the second

Stomach, liver, and spleens, of the Porpoise. CXLIV". (From stomach, beyond which

a drawing by R. O. the prep. dry, is in Mus. Coll. Chir.)

orifice it is continued in a, a.

the form of a dilated ovate cavity, ib. It is lined with a cuticle, or thick laminated epithelium, and its inner surface is

The fig. 354 has been taken by the writer of CL". from CXXII'. vol. xiii. pl. III., fig. 2. The foregoing description is from dissection of the specimen of Cholapus didac tylus which died at the London Zoological Gardens, in 1851, and in which the arteries were previously injected. See CXLVII". p. 167, No. 553 c.

beset with small ruga. A number of large irregular projections surround the aperture leading to the second cavity, and are calculated to prevent the passage therein of any substances save such as are of very small size. Notwithstanding the nature of the lining membrane the digestive processes are considerably advanced in the first cavity, which does not act simply as a reservoir. It is probable that the secretion of the second stomach regurgitates into the first and assists in producing the dissolution of the fishes, the remains of which are usually found in it. The thick epithelial lining terminates abruptly at the small orifice leading into the second stomach, ib. b. The interior of this cavity presents a series of close-set longitudinal wavy rugæ, laterally indented into one another. The internal layer is thick, and mainly consists of unusually long gastric tubes perpendicular to the two membranes which enclose them. The membrane next the cavity of the stomach is smooth; the one external to the fibres is a vascular and cellular tunic, and is invested by the layer of muscular fibres, continued from the preceding cavity. The communication with the third stomach is near the lower end of cavity, b. The third compartment is a small round vascular cavity, into which the second opens obliquely: it is lined by a smooth and simple villous tunic: it is not visible exteriorly, and does not exceed an inch in length in the Porpoise, but in the Hyperoodon is about 5 inches long. The fourth cavity, ib. c, c, is long and narrow, and passes in a serpentine course almost like an intestine; the internal surface is smooth and even, but villous. It opens on the right side into the duodenum, ib. d, which is much dilated. The pylorus is a smaller opening than that between the third and fourth cavities,'

In Balanoptera the œsophagus enters obliquely at the back part a little beyond the upper end of the first cavity: the second cavity is larger and longer, in proportion to the first, than in Phocana: the rugæ are longitudinal, very deep, and here and there united by cross bands. The third cavity is very small, and, as in the Porpoise, appears only to be a passage between the second and the fourth. The latter is more definitely divided into two successive cavities.

The duodenum commences in all Cetacea, by so considerable a dilatation that it has been reckoned among the divisions of the complex stomach. In the Porpoise it soon contracts to the

xx. vol. i. p. 175, no. 569 c. This description I appended, together with the other paragraphs between brackets, to the Art. Cetacea (CLI), the translation of which was confided to me by the Editor.

ordinary diameter of the small intestines

about 1 inch: these are continued for between 40 and 50 feet to the vent. Broad and well-marked longitudinal folds of the lining membrane extend along the major part of this course: and the same character obtains in other Delphinidæ. In Balanoptera the longitudinal folds are wavy, run into each other, and are connected by smaller oblique or transverse folds: the submucous areolar tissue is very loose and abundant. In Hyperoodon the complexity is carried out to such a degree as to occasion a sacculated structure of the mucous coat through nearly the whole tract of the intestinal canal. The orifices of the larger pouches are directed vent-ward: their cavity is divided into smaller cells. They begin gradually in the duodenum near its last abrupt bend, and subside near the

anus.

In Balanoptera the ileum opens in a valvular way into a comparatively short colon, leaving a cæcum of about 7 inches in length, and of a simple conical form: in the specimen 17 feet long, of Bal. rostrata, dissected by Hunter, he records the length of the small intestine at 28 yards, of the large intestine 2 yards; and notes that he never found air in the intestines of this tribe.' 2

The complicated stomach and long intestinal canal of such carnivorous Cetacea as the Grampus have other relations than to the nature of the food: they are necessitated in the present order by the amount of nutriment which must be had from it. In no other carnivorous mammals is so great a quantity of blood and fat to be obtained from the raw alimentary material: in none are such active and extensive molecular changes concerned in the production and maintenance, under adverse external conditions, of so high a temperature of the body. The digestive system and processes are therefore perfected in these warm-blooded marine airbreathers to meet the contingencies of their aquatic life.

§ 334. Alimentary canal of Sirenia.-In these more slothful, tropical, or sub-tropical marine mammals, although the food is of a low vegetable kind, the digestive and assimilative tract differs from that of the carnivorous Cetaceans rather by a minor than a major degree of complexity. The stomach, it is true, shows appended sacculi, special glands, and a subdivision of the general cavity, not only through constriction, but by a difference of structure in the lining membrane. It is of considerable length, and nearly equally divided into a cardiac and pyloric portion. In the Manatee the œsophagus terminates at the middle of the cardiac porCCXXXVI, vol. ii. p. 115. XCIV. p. 361.

2