The inner, or what, with Bichat, we shall call the mucous coat of the intestinal canal, is the most impor tant, both in an anatomical and physiological point of view, as it is on this membrane that the action of the intestines, in the preparation or separation of chyle, more immediately depends. This mucom, membrane is ex ceedingly voluminous; the extent or its surface being increased by numerous puckerings and doublings. com monly called by anatomists cs. These internal folds run obliquely across the intestinal canal, and considered separately, are hut narrow; but from their number, and the closeness with which they are arranged, tend to tor re rase the internal 8iIktCe of the r anal to ;:t IcaSt dOIIIJC its etiterlial stn Iar e. "I'Lese folds art_' most nnntcrous iu the small inte stifles, hut gradtrilly diminish in Humber towards the colon, and near the ca cum they almost entirely disappear. There are but few of these holds in the colon, but in the rec tum they are inure numerous ; and in the interior of this bowel there is beside s a number or folds running longi tudinalfy, and commonly r ailed the pillar., of the rectum. These art: most remarkable towards the anus, and ap pear to arise chiefly Irons the contraction 'ff the circular muscular fibres, Nyllich is strongest at that part. The projecting surface of the folds has a rough or shaggy appearance, and hence the nowous membrane has been called the %dime-, coat of the intestines. There are here numerous orifices, opening into the cavity of the canal; some of whit are the outlets of the exhalant vessels, that pour out a mucous Iluid into the cavity ; and others, which are so small as scarcely to be detected by the na ked eye, are the mouths of those absorbent vessels call ed luctrul.y, which take up the nutritious fluid the intestinal canal, and convey it into the general circulation.
That projection of the sacral extremity of the small intestines into the ea:cum, t, pith forms what is called the calve of the colon, is produced chiefly by a dou bling of the mucous membrane of the cxeum, which, tOlding hack upon itself, is united to a similar doubling cooling from the extremity of the small imestincs, so that, at its middle, this valve is formed by lion- layers of the mucous membrane. It is not easy, by a descrip tion, to con', ey an accurate idea of the strut lure of this valve ; it is best understood by examining the intestine in the dead body. To do this with advantage. it is pro per to cut out that portion of the intestines which com prehends the terminotion of the ilium, the excum, and he commencemeht of the colon ; to sec tire this last by a ligament, then to distend tic exeunt with air intro duced through the ilium, vvhich must then be secured, and the inflated portion suffered to dry. On opening he talcum towards that part which is opposite to the entrance of the ilium, NI e shall observe a large semilunar fold, transversely situated, haN its upper part turned towards the colon, its lower towards the ( ,ceuni, with a convex border next the opening of the ilium, and the side of the c,scum to which it is fixed, and a loose con cave border divided in the middle into two is by a long chink directed towards tile ilium, and hanging ii,to the cavity of the ca c001.* Sec Ilichat, .That. D(scriPt. tom.
p. 433.
The intestines are supplied with numerous arteries, nerves, and absorbents, the nerves being derived partly from the tar ,'u urn, hut chiefly from the great sympa thetic. The origin of their arteries, and of those be the stomach, will he given in the table of arteries. A great number of minute glands are also found between the mucous membrane and the mus cular coat, which are distinguished into simple or soli tary and conglobate, though they are so small as to be -teldom The intestinal canal possesses a peculiar motion back wards and forwards, or rather in a waving direction, by which its contents are repeatedly subjected to the action of the exhalants and the lacteals, that open on the sur face of the mucous folds. This has been called the ;ermicular or peristaltic motion (Attie bowels. It is easily seen on opening- au animal that has been killed soon at tur taking hooch.
The food, after being mu:a/cured in the mouth, passe through the gullet into the stomach, wIR re it is rc taiue till it be reduced to a pulpy mass, commonly called chyme, from winch, in the py brie portion ol the stomach, the chylr beg-ins to be separated. "File chyli lication is completed in the duod, /rum ; and cc pile the alimentary mass is traversing the small intestines, the greatest part. of the chyle is taken up by the lacteals, while the more solid and exerenre parts pass through the colon and attune, to be evacuated by the U11118. See PH YSIOLOGY.
Resides the peritoneal coat, which forms the outer covering of the intestinal canal, there are several mem branes connecting its ditlerent parts, NS hid) we must here briefly notice.
From the great curvature of the stomach downwards to within a lew inches of the pubis, hangs a fatty, NILS (Allay membrane, between the convolutiobs of the bowels and the membrane that lines the sides of the belly'. This called the great omeutum, the remains of which are seen at Q, H, '1', S, Fig. I I. Pt. XIX. This part is sometimes called the gustroc9lic omentum, fru.n being common to the stomach and colon ; and a reflection the same membrane, extending between the ezecum and the right side oh the arch of the colon, is called the colic-omentunt, similar membrane, commonly called the lesser omentun 1, 'and by II alter flu inbrana inacilrathr, from its being less abundantly supplied with fat, con nects the back pait of the stomach cc ith the duodenum and the liver. These fatty membranes serve to lu bricate the surface of the bowels, and facilitate their motions over the neighbouring parts. "Their direction and conneciions are well expressed in two figures of Haller ; see his icoac.s. ./nutomicx,and his Olicra Minora, tom. i. p. 576. though the engraving of these last figures is not equal to that of the larger work. Two fine copies of these figures are also given by Dr Parr, in his .1171, _Lon Ion (Lica! The which connects together the small iwestines with its ceminuations, the and the will be noticed in a future chapter.