Edentata.—The stomach of this order differs greatly in different genera. Most of them possess a simple organ ; the cardiac ponch of which is large and globular, while the pyloric extremity is conical, and is some times almost absorbed into the spherical cavity. A single genus, the Manis, adds a further distinction to these two parts in the shape of an internal fold of mucous mem brane; and one of its species exhibits a long blind sac, springing from the right of the pyloric aperture. In the Tardigrade genera the stomach assumes much of the complexity seen in the Ruminantia. For it has two cavities, a cardiac and a pyloric, which, if regarded from the exterior, look like mere exaggera tions of the distinction mentioned above, but, when examined internally, are seen to be divided by prominent folds, and by differences in the character of their mucous membrane. Thus the cardiac pouch has a dry epidermoid lining, and is subdivided by a fold into two parts, and prolonged into a short blind tube, while the pyloric sae has a soft and delicate mu cous membrane, and more muscular parietes. And its interior is also subdivided, by a fold of membrane, into a terminal part, which is analogous to the fourth stomach of the Ru minants, and an intermediate cavity, which resembles the third stomach of the same order in its possessing dentate processes, and a direct communication with the cesophagus. The latter tube also exhibits a cul-de-sac, which is sometimes further divided by folds.
The form and length of the remainder of the canal is subject to great variety. Its mesentery is very long. In many genera there is no distinction of the inte.tine into large and small. In some there is no trace of a cwcum. In others there are two of these tubes, which occupy the confines of the large and small intestines, and open by what are sometimes extremely minute apertures.* The Ruminantia are remarkable for the com plete subdivision of their stomach into four dis tinct cavities. The first of these, the rumen, or paunch, is generally, of very great size. It is situated to the left of the cesophagus, fi•om which it receives the food when first swallowed : it has a villous texture, but its minute conical processes are covered by a dense white pave ment epithelium. The second cavity, the honeycomb or reticulum, is so called from the appearance of its mucous membrane, vvhich, in all other respects, has the same structure as that of the preceding cavity. The third portion, the maniplies or psalterium, is named from the many longitudinal plies or folds which occupy its interior. In the Camel, the circumference of the cells or excavations of its reticulum and paunch have been long recognized as containing muscular fasciculi, the contraction of which enables these cavi ties to retain water free from admixture the general contents of the stomach. And eight or nine years ago, the author discovered that all these projections froin the surface of the ordinary Ruminant stomach,—viz. the villi, honeycombs, and plies—are constructed chiefly of unstriped muscular tissue, lined by scaly epithelium. The uses of such a structure are
too obvious to need any comment. The fourth cavity. or abonzasum, is the true stomach: it secretes the gastric juice, and possesses the ordinary tubular structure. As regards the uses of these cavities, the bolus is probably. moulded for rumination in the honeycomb, and is thence regurgitated into the gullet ; while a muscular fold forms a direct pathway for the ruminated food to pass at once from the cesophagus to the maniplies.
Pachydermata.—The Elephant has a stomach which is elongated, and subdivided by very numerous folds. In other respects it is simple. That of the Rhinoceros is similar ; but the cardiac pouch is devoid of folds. The shorter stomach of the Pig is divided internally by two folds of mucous membrane into three por tions :— a cardiac pouch, a pyloric extremity, and an intermediate portion, which receives the cesophagus. The lesser curvature, and the back of the cardiac pouch, are both occu pied by a white and dense epithelium, which is similar to that of the cesophagus, and forms a broad quadrilateral band along this aspect of the interior. In the Pecari there are ex ternal indications of the same subdivisions : but the white epithelium extends over a wider surface; so that it is only the pyloric third, and the lower parts of the middle and cardiac pouches, which exhibit the proper gastric or tubular structure. In the Hippopo tamus, the stomach is long and tubular, and is complicated by the addition of two pouches, hich have a size almost equal to its own, and communicate with its cavity by corre sponding orifices on the right of the cesophagus and at the back of the cardia. The internal surface of the organ is so folded as to allow the alimentary bolus to enter either of these t wo cavities.* Tne stornach of the Solipeda has a rounded shape, and a cardia and pylorus w hich are close to each other. The cardiac half of the org,an is lined by a white epidermis, which terminates by an abrupt dentated margin.
In all these three orders — Ruminants, Pachyderms, and Solipeds— the intestine is characterized by great leuf,ith, width, and convolution, and by. the possession of a capa cious cwcum. Thus, in the Ruminant sheep, the intestine is thirty times the length of the body. And although in the Soliped horse this proportion sinks to fifteen or twenty, still the sacculation of the cmcum and colon which ob tains in this and the Pachyderinatous order per haps compensates such a diminution in length. The ilio-cwcal valve is represented by a narrow passage, the mucous membrane of which forms six or eight thick longitudinal folds. The cwcum, smallest in the Pachyderm, attains its maximum size in the Soliped ; being, in the Horse, two feet long, and thrice as capacious as the stomach. In one Pachyderm—the Cape Hyrax—two additional aecal tubes open into the large intestine by wide apertures.