The small intestines commence at the pylorus and after many convolutions terminate in the large intestines. They measure on an average about twenty feet in length in the adult. For convenience they have been divided into three parts--the duodenum, which extends from eight to ten inches beyond the pylorus; the jejunum, which occupies two-fifths, and the ilium, which occupies three-fifths, of the rest of the canal. The mucous membrane, the interior coat, is the most important to the function of digestion. There are permanent folds, shelf-like processes, of the mucous membrane, called valvular conniventes. There are also villi and glands, as the glands of Lieberkühn, of Peyer, and of Bruner. The glands of Lieberkühn are thickly distributed over the whole surface of the large and small intestines. The glands of Peyer are exclusively in the small intestine. They are found in greatest abundance in the lower part of the ileum near to the ileo-cæcal valve. They are met with in two conditions, viz., either scattered singly, in which case they are termed glandulæ solitairæ, or aggregated in groups varying from one to three inches in length and about half an inch in width, chiefly of an oval form, their long axes parallel with that of the intestines. In this state they are named glandulæ agminatæ. The latter are almost always placed opposite the attachment of the mesentery. In structure they are analogous to lymphatics or absorbent glands, and their office is to take up certain materials from the chyle, elaborate them, and subsequently discharge them into the lacteals, with which vessels they appear to be closely connected. Bruner's glands are confined to the duodenum; they are most abundant and thickly set at the commencement of this portion of the intestines, and are provided with permanent gland ducts. The villi are confined exclusively to the mucous membrane of the small intestines. They are minute vascular processes, from a quarter of a line to a line and two-thirds in length. There are about fifty to ninety in number to a square line. Each villus consists of a small projection of mucous membrane, and its interior is supported throughout by fine retiform or adenoid tissue. Two or more arteries are distributed to each villus, and from their capillaries, which form a dense network, proceed one or two small veins, which pass out at the base of the villus. The lacteal vessels enter the base of each villus, and passing up in the middle extend nearly to the top, where it ends commonly by a closed and somewhat dilated extremity. The office of the villi is the absorption of chyle from the completely digested food of the intestines.