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NEW YORK, WILLIAM JACKSON; BOSTON, JOSEPH H. FRANCIS;

PHILADELPHIA, ORRIN ROGERS; BALTIMORE, W. N. HARRISON.

MDCCCXXXIX.

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INTESTINES are that portion of the digestive canal | ducts by which they are conveyed open into the intestinal into which the food is received after it has been partially canal, near the middle of the duodenum, or about six inches digested in the stomach, and in which its further assimila- from the aperture by which the food passes from the stotion, the separation and absorption of the nutritive matter, mach; and immediately beyond the orifices of these ducts and the removal of that which is excrementitious, take the villi are of great size, and thickly set on promment place. In an adult, the intestines consist of a convoluted folds of the mucous membrane, called valvulæ conniventes. tube of from 30 to 40 feet in length, and are, from the dif- These folds, at the same time that they increase the extent ference of their diameters in different parts, divided into of surface for absorption, serve to entangle the semifluid small intestines, which comprise about the first four-fifths, mass of food, now completely digested; they are most nuand large intestines, which constitute the other fifth of their merous and prominent in the jejunum, where absorption length. The former again are divided into the duodenum, is carried on earliest and most rapidly, but are found to a into which the ducts from the liver and pancreas open, and slighter extent throughout the whole of the small intestines, in which the chyme from the stomach is converted into The absorption of the chyle is effected by the villi, each chyle (DIGESTION; CHYLE]; the jejunum, in which the of which is composed of a minute tube, which is the termiabsorption of the nutritive matter of ihe food is principally nation of a branch of the lacteal or absorbent system of effected; and the ileum. The large intestines are divided vessels, and is ensheathed in a delicate tissue containing a into the cæcum, colon, and rectum.

net-work of capillary arteries and veins. The form and The walls of the intestinal canal are composed of three function of the villi may be best demonstrated in an animal principal coats or niembranes. The exterior, which is smooth which has died suddenly after a full meal; they then apand polished, is called the peritoneal, and its principal use pear turgid, and stand erect, filled with a whitish milky is to permit the free motions of the intestines within the fluid, the chyle, which, as fast as it is absorbed by them, is abdomen, and of their several convolutions against each conveyed by numerous converging streams into the main other, by rendering the effect of friction as slight as possible. trunk of the absorbent system, called the thoracic duct, Next to and within the peritoneal coat is the muscular, through which it is gradually poured into the blood of the which is composed of two layers of fibres; an external, in left subclavian vein, at a short distance before it enters the which they are directed longitudinally, and an internal, of right side of the heart. [HEART.] The whole process of which the fibres encircle the intestine. By these the mo- absorption is not unaptly compared to that by which the tions of the intestines and the propulsion of their contents fluids are conveyed from the earth through the roots into are effected; the longitudinal fibres tending to shorten the stem of a plant; the villi of the intestine being repreeach portion of the canal, while the circular contract its sented by the tufts of hair-like spongioles which are placed diameter; and the two sets together producing a motion of at the terminations of the fibres of the root. the tube somewhat like that of a worm, whence it has re- The portion of the food which is unfit for the nourishceived the name of vermicular motion. Beneath these ment of the body is forced onwards by the vermicular molayers, and separated from them by a stratum of cellular tion of the intestines, and being mixed with the resinous tissue, which has been sometimes called the fourth or ner- and other excrementitious substances secreted by the liver vous coat, is the mucous membrane, which is the most im- and other glands, is conveyed through the whole tract of portant part of the intestinal canal. It is everywhere beset the intestines; and after it has been exposed to the absorbby innumerable minute glands, by which the secretion of ing vessels, which are placed in greater or less abundance mucus and the other intestinal juices is carried on. In the in every part of the canal, so that not a particle of nutrismall intestines it has a fine velvet-like surface, made up of ment can be lost, the residue is voided. minute thickly-set hair-like processes, or villi, which are INTONATION, in vocal music, is the tuning of the about $th of an inch in length, and stand up so that their voice—the singing true or false-in tune or out of time. tops seem to form a smooth surface like the pile of velvet. Correct Intonation is the first requisite in a singer; this These, as well as all the rest of the mucous membrane, are wanting, all his other musical qualities, however good, are protected from the irritation which the immediate contact unavailing; of foreign substances would produce, by a covering of an INTRA'DOS and EXTRA'DOS, the lower and higher inorganic cuticle of extreme delicacy, called epithelium. curves of an arch. [ARCH.]

The principal functions performed by the intestines are INTRICA'RIA, a small Polypiser from the oolitic rocks the conversion of the chyme (DIGESTION; Gastric Juick] of France, allied to Cellaria. (M. Defrance, Dic. des Sci. into chyle, the absorption of the latter, and the removal of Nat.) the innutritious parts of the food and of a considerable INTUITION (intueri), the most simple act of the reason quantity of excrementitious matter. In the first process, or intellect, on which, according to Locke, depends all which constitutes the last stage of digestion, the secretions the certainty and evidence of all our knowledge; which of the liver and pancreas take an important part: the certainty every one finds to be so great, that he cannot P. C., No. 788,

VOL. XIII.-B

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