Page:Encyclopædia Britannica, first edition - Volume I, A-B.pdf/306

 A N A T Ths duodenum having arifen from the pylorus, is immediately bent a little backward, and obliquely downward ; then it bends a fecond time toward the right kidney, to which it is a little conne&ed, and from thence palfes before the renal artery and ve-n, afcending infenfibly from right to left, till it gets before the aorta and laft vertebrae of the back. It continues its courfe obliquely forward, by a gentle turn. Through this whole courfe, the duodenum is firmly bound down by folds of the peritonaeum, efpecially by a tranfverfe duplicature which gives origin to the mefocolon. The villi of this intefline are thicker than in the flomach ; but the texture of them in man is not like hairs, as they are commonly reprefented in figures; but rather like that of a fungous granulated fubftance, compofed of an infinite number of very fine papillae of different figures, in which we fee, through a microfcope, a Ciuhitude of depreffed points or pores, by which their whole furface feems to be pierced. By the fame help we obferve, on different places of the inner, furface of this inteftine, feveral round villous tubercles, rifing like fmall verucae at different diftances from each other. This fubftance fu(tains an infinite number of capillary veffels, of different kinds; for befides the blood-veffeis, we fometimes obferve a great number of white' filaments which run through it, and end at its inner furface, like fo many capillary roots of the yeffels, called venae ladteae. The internal furface of the duodenum is furnifiied with a great number of fmall flat glandular tubercles, raifed on the fides, and depreffed in the middle, by a kind of foffula; and they are more numerous near the beginning of this inteftine than any where elfe. Thefe glands appear like little bladders, with the orifices turned toward the cavity of the inteftine, and the bodies fixed in the fpungy fubftance next the nervous coat. They furnifh a particular vifcid fluid. In the inner furface of the duodenum, almoft at the lower part of the firft incurvation, and on the fhorteft fide, there is a longitudinal eminence, in the point or apex of which lies a particular opening, which is the orifice of the duftus bilarius, within which the duttus pan■creaticus likewife opens. INTESTINUM JEJUNUM. The jejunum, fo called, b caufe it is oftener found empty than the ilium, begins at the laft incurvation of the duodenum, and is there connetfted to the beginning of the mefocolon. From thence it bends downward from left to right, and obliquely forward, or fiom the vertebras, and makes feveral convolutions, which lie chiefly in the upper part of the umbilical region. Through all this courfe it is connefted to the mefentery. The jejunum and ilium may be.diftinguilhed by dividing both inteftines into five parts; and to allow nearly two fifths to the jejunum, and three fifths and a little more to the ileum.

o M Y Part VI. The coats of the jejunum are nearly of the fame ftructure with thofe of the duodenunvbut thinner. INTESTINUM ILEUM. The convolutions of the inteftinum ileum furround thofe of the jejunum on the two lateral and lower fides, and it paffes in a winding courfe from the left fide, by the hypogaftrium, the right where ittheterminates a little below thetoright kidney,fide,joining inteftina cralfa. The ftrudure of the ileum is much the fame with that of the jejunum ; only the internal duplicatures or valvulae conniventes decreafe gradually both in number and fize. Tfo Intestina Ckassa in general, #«</Inteftinum caecum in particular. The great inteftines are one continued canal, divided into three portions, like the fmall ones. This canal begins by a kind of facculusor bag, which is reckoned the firft of the three portions, and called caecum. The fecond portion, called colon, is the longeft of the three, and is diftinguiftied from them by a great number of particular eminences or convexities, which appear on its outer furface through its whole length. The laft portion is named reftum, being more uniform, narrower, thicker,' and much (horter than the colon. The ftruflure of the great inteftines is nearly the fame with that of the fmall ones, in regard both to the number and difpofition of their coats. They are (horter, and have fewer convolutions, but are much more capacious. The coats in general are ftronger, but efpecially the mufcular coat. The inteftinum cascum is only a round fliort broad bag, the bottom of which is turned downward, and the mouth or opening upward. It lies under the right kidney, and is hid by the laft convolution of the. ileum. It is about three fingers breadth in length, and its diameter is more than double that of the ftnail inteftines. On one fide of the bottom of the caecum lies an appendix, refembling a imall inteftine, nearly of the fame length with the caecum, but very flender. It is termed appendicula vermiformis, from its fuppofed refemblance to an earth-worm. Its common diameter is not above a quarter of an inch. By one extremity it opens laterally, and a little obliquely, into the bottom of the caecum ; and the other extremity is clofed, being fometimes greater, fometimes fmaller, than the reft of the appendix. Through the membranous or common coat of the caecum, we fee three white ligamentary bands, which adhere very clofely both to the outer and mufcular coat. One of them is hid by the adhefion of the mefocolon; and all the three divide the caecum longitudinally into three parts more or lefs equal. They all unite in the appendicula vermiformis, and cover its whole outer fide immediately under the common coat. I N T E-