• e shall conclude this article with a notice of some of the most striking peculiarities presented by the digestive organs in the lower animals.
In the mammalia, we have three different forms of stomach—the simpla, the complex, and the compound. In the simple form, the organ consists of a single cavity, as in man, hut the form may vary to a great extent. It is most simple and relatively smallest in carnivorous animals. This is the most common form of mammalian stomach. In the complex stomach, that viseus is made up of two or more compartments communicating with one another, but often without presenting any marked difference of structure. The kangaroo, the porcupine, and the squirrel, afford good examples of this form of stomach. In the cetaqea, the stranaelr'consists of from five t_o seven Cavities, that com municate with each' Other; bait Whether their' ftinctions tire similar or different is not known. The compound stomach occurs in the ruminants (the cow, sheep, camel, etc.); it consists of four distinct cavities, differing very materially in their size, and in the arrangement and structure of the lining mucous membrane. The first, and by far the largest cavity, is the paunch or rumen; it occupies a great part of the abdominal cavity, and is the receptacle into which the food is received when first swallowed. The second cavity is termed (from the peculiar arrangement of the lining membrane, which forms deep polygonal cells) the honey-comb or reticulum. The third cavity presents a foliated appearance internally, and is hence popularly known as the manyplies. In anatomical works, it is sometimes termed the psalterium, and sometimes the omasum. The fourth division, termed the reed or abomasum, is somewhat of a pyriform shape, and is the true digestive stomach, in which alone gastric juice is secreted, all the preceding cavities being merely for the purpose of preparing the food for the more essential changes which it is here destined to undergo. The food first passes in a crude unmasticated state into the paunch, which, like the crop of birds which we shall presently notice, serves as a receptacle for the food until the act of feeding is concluded, and moistens it with the fluid secreted from its walls. The water, however, which the animal drinks, seems to
pass directly into the second stomach. During rumination, small portions of the food pass from the paunch into this second stomach, from whence they are returned, in the form of pellets, to the mouth, where they undergo thorough mastication, and are then returned, as a pulp, by the esophagus directly into the third stomach. The direction of the food into one or other of these cavities is altogether independent of the will, and results from a peculiar arrangement and property of the lower end of the esophagus, which does not terminate at its opening into the paunch on one side, and the second stomach on the other, but is continued onwards as a deep groove or semi-canal, with two lips. If these lips come in contact, they form a perfect canal, leading directly to the third stomach; while if they remain open, the food passes into the first or second stomach. The dry food first swallowed opens the lips and escapes into the paunch, while the masticated food, being soft and pulpy, passes along the groove, without open ing its lips, into the third stomach. Here it is diffused over a large surface of mucous membrane, and doubtless undergoes certain changes before entering the fourth or true stomach. In the camel, the dromedary, and the llama, numerous rows of large quad rangular deep water-cells are developed on the parietes of the second stomach, and on the part of the paunch next to that cavity. These cells are surrounded by muscular fibers, which, by their contraction, exclude the food from their interior, and by their gradual opening, the water is allowed to mix in successive small quantities with the food. It is by this arrangement that these animals only require to drink at compmmtively long intervals. The intestinal canal of the ruminants is of great length, being some times, as in the sheep, more than thirty times the length of the body of the animal; and in herbivorous animals generally, as compared with carnivorous, the canal is very long.