(From duodeni, twelve). This intestine is thus named from a supposition that its length does not exceed the breadth of twelve fingers; and if measured with the ends of the fingers, the idea is sufficiently correct: it is also called dodecadactylon, ecphysis,fiorto-rarium. It begins at the right orifice of the stomach behind the liver; runs backward, and obliquely downward; then turns a second time towards the right kidney, to which it is attached by the cellular membrane. It next passes between the kidney and liver, across the spine about the last vertebra of the back; and it comes out on the left side, behind the root of the mesentery: as soon as it arrives at the mesentery, it forms the jejunum. It is the widest and shortest of the small intestines; indeed it is sometimes called ventriculus succen-turiatus, an office we have already assigned to it (see . Digestion). Its extremity;next the jejunum, is fixed in a course almost perpendicular upwards. It is not entirely covered with the peritonaeum, nor contracted by a mesentery; but attached to the neighbouring parts. Its outer coat is surrounded by a loose cellular membrane; the villi in its inside are thicker than in the stomach, and its texture resembles a fungus, as the inner coat is loose, and folded into what are called valvulae conniventes, like the gills of a mushroom. On the edges of these valves are very fine papillae of different shapes, apparently pierced with many holes, seen only by a magnifier; and in other parts are villous tubercles at different distances from each other. This villous substance contains many capillary vessels, not only conveying red blood, but apparently lymph or chyle. Several follicles are discovered in the cellular substance, which have been considered as the origin of the lacteals. These have been called, from their discoverer, the ampullae of Liberkuhn.

In the inner surface, almost at the lower part of its first turn, there is a longitudinal protuberance, at the point of which is an opening, where the pancreatic and biliary ducts discharge their contents.

As its form is much like that of the stomach, so is its use: it is furnished with fluids peculiar to itself, since not only numerous small glands were discovered by Brunnerus in it, but the pancreatic juice, mixing with the bile, accomplishes, in this intestine, the further elaboration of the chyle: thus the digestion of the aliment, begun in the stomach, is completed in the duodenum. (See Duodenalis arteria et vena.) Its nerves are the middle plexus of the semilunar ganglion, and some filaments of the plexus stomachicus and hepaticus. The duodenum is connected with the oesophagus by the same coats, and hence they communicate with the coat which surrounds the fauces and the mouth. Like the stomach the duodenum hath a very extensive nervous connection with the other parts of the body.

Of such importance is the duodenum, that Sylvius thinks it the seat of almost all the disorders in the physician's province. Van Helmont agrees with him; and the influence of this part is certainly considerable.

In the circulation, no morbid matter can be discovered; in the stomach and duodenum, a stagnation, and consequent degeneracy are often produced: if the bile and other fluids stagnate in the duodenum, they soon occasion great anxiety, with other unpleasant symptoms. From this source, vie. the morbid contents of the duodenum, many disorders have been traced; and the opinion is further confimed by the success of emetics, and of gentle purgatives, in the cure of many chronic complaints. Emetics often evacuatethe contents of the duodenum by a continuation of the inverted motion, as we find by their discharging bile after their continued action. See Monro's Observations on the Intestines, in the Edinburgh Essays, and Frederic Hoffman on the Duodenum.