THE SMALL. IN rESTINE. The serous coal of the small intestine consists of a single layer of epi thelium or endothelium (forming the peritoneal surface) resting upon a thin layer of delicate connective tissue. Beneath this lies the coat composed of (a) an outer portion in which the smooth muscles are disposed longitudinally the long axis of the intestines and conse quently known as the longitudinal muscular coat, and (b) an inner or circular coat in which the muscle-cells are disposed transversely to the axis of the lutist Hies. Thi• two layers of muscle are separated by more or less connective tissue. The subinueous eoat COnSi•is of loosely arranged bun dles of fibrous and elas tic connect ive t issue, with a rich plexus of mood-vessels, lymphat ics, and nerves. Through the subinucous coat are distributed, at varying intervals, cir cumscribed ilia of I y p 11 i tissue or lymph • nodule,. These may occur singly (soli tary glands, or folli cles), lying in both sub mucosa and mucosa, and may even project slightly from the free surface of the mucous membrane. I tr else, instead of a single nodule, there may be a collection of nodules forming what is known as l'eyer's patches, which are found mainly in the 'Usually from 20 to 30 nodules constitute a patch. Like the solitary nodules, they lie in both subinueosa and mucosa and often project upward to tlic free surface of the intestine. Finally, the mucous membrane of the small intestine is thrown up into transverse or ob lique folds, which involve also the stilanueons coat, and which arc known as the ra Ow colnirc Wes. In addition to this the mucous membrane over the valvuhe is studded with minute projections known as which are characteristic of the small intestine. The mucous membrane consists of three coats, the epithe lial coat, the strong, and the museularis mucosa..
The epithelial coat is com posed of a single layer of columnar epithelium, which covers the surface of the mucous membrane. Dis tributed at intervals among the columnar epithelial cells are clear, transparent cells, which. on account of their shape, are called goblet cells, or, because of their secretion. mucous cells. The epithelium rests upon a basement membrane, beneath which lies the stroma. The latter is composed of delicate connective tissue and more or less diffuse lymphoid tissue. It tends up into the villi and supports the vessel., nerves, and glandular structures. From the bottom of the depressions between the villi, glands tend down into the stroma. These are tubular glands, called the crypts of Liebcrkiihn, and tend down to the museulam i.s tnueus;c. 'Flue glandular epithelium is in type, lower than that on the surface of the mucous membrane, with which it i, directly Numerous goblet eel Is are distributed :uuuug the oolumiutar cell.. Im one portion of the small intestine much more elaborate glands :ur found. ']'hey are ated in the duodenum amid are known as the glands of ner. They arc compntutd bular glands, whose acini arc situated iu the sub nnwosa and whose ducts pass up between the crvpts of Liebei'kii1imt and empty between the yilIi. The museularis mslcosa is the in nermoct laver of the mucous It is composed of smooth muscle - cells, whn.e long axes correspond mainly to the long axis of the intes tine. At certain points a more or less complete internal circular layer is present. See GLASns.