Page:The Hog.djvu/130

128 formed of that membrane which invests and retains in its proper position every portion of the contents of the belly. The second layer is muscular, and by its action propels the contents of the stomach gradually onward's. The office of the third is to lubricate the innermost coat, and for this purpose, it is supplied with numerous glands surrounded by cellular tissue. The fourth or lining coat is soft, villous, and, in a healthy state, always covered with mucus. The food, having been sufficiently converted into chyme by the action of the stomachs, is gradually propelled through the pyloric orifice by

or first intestine, where it is submitted to the influence of two fluids, the one secreted by the pancreas, the other by the liver, and the combined action of which separates the nutritious from the worthless portion, causing the former to assume the appearance of a thick whitish fluid, and the latter that of a yellow pulpy substance. It next passes into

where it undergoes still further alteration, and whence a considerable portion of it is taken up by the lacteal vessels which open into these two small intestines, and conveyed away to nourish the frame, and become mingled with the blood and supply the waste in it. These intestines are of equal diameter in the pig throughout their whole extent, and the termination of the jejunum and commencement of the ileum is by no means distinctly defined; the latter is, however, longer than the former, and opens into

with a valvular opening close to the aperture into the colon. The cœcum is a kind of bag supplied with numerous secretory glands, which furnish it with a fluid which once more acts upon those portions of the digested food which reach it, extracting from them any nutritive portions which may chance still to remain. The matter having reached the base of this intestine, is returned by the muscular action of its coat, and being prevented by the valve from reentering the ileum, passes into

the largest of the large intestines, some of the convolutions of which equal the stomach in size, while others are as small as the small intestines. Here the watery parts of the mass are extracted, and the residuum or hard fæcal portion is retained for awhile, and finally expelled through the rectum. It will be readily imagined that this