The jejunum and the ileum alone occupy nearly three-fourths of the 

 whole length of the digestive canal ; they are straiter than the duodenum, 

 and do not dilate so readily, because the peritoneum, which forms their 

 outer covering, lies over their whole surface, with the exception of the 

 posterior border at which their vessels and nerves enter. It is along 

 that border, that they are fixed to the mesentery, a membranous band 

 formed by a duplicature of the peritoneum, which contains the vessels 

 and nerves going- to the jejunum and ileum, which prevents knots from 

 forming in the intestines, and is a security against the occurrence of 

 intus-susceptio. It is well known, however, that in some rare cases, in- 

 tus-susceptio does take place, with utmost danger, of the patient's life, 

 who generally dies in the agonies of insufferable cholic pains, which 

 nothing can alleviate. The progress of the food, along the small in- 

 testines, is retarded by its numerous curvatures, very aptly compared 

 by some physiologists to the windings of a meandering stream which fer- 

 tilizes the soil it waters. These numerous convolutions of the intestinal 

 canal favour the long continued presence of the food within its cavi- 

 ty, so that the chyle expressed from the excrementitious part by the 

 peristaltic contractions of the intestine, may present itself to the inha- 

 ling mouths of the lacteals, by which it is to be absorbed. These chy- 

 lous absorbents are in greater number on the surface of the valvulae 

 conniventes, which are circular folds of the inner membrane, and these 

 are at a greater distance from each other, the nearer they are to the ter- 

 mination of the ileum. The valvulae conniventes not only slacken the 

 progress of the food, but by their projections, they sink during the con- 

 traction of the bowels, into the alimentary mass, and the lacteals on their 

 surface take up, from its inmost part, the chyle which they are destined 

 to absorb*. 



The number of the valvulae conniventes diminishes with that of the 

 lymphatics. The progress of the alimentary substance is gradually ac- 

 celerated, as it parts with its nutritive and recrementitious particles. A 

 quantity of mucus, secreted by the internal membrane of the small intes- 

 tines, envelopes the chymous mass and promotes its progress, by lubri- 

 cating it : this intestinal mucus thrown out by the exhalant arteries, im- 

 bues it, renders it liquid, and adds to its bulk. This fluid which seems to 

 partake of the nature of albumen and gelatine, and to hold several saline 

 substances in solution, is, for the greater part, recrementitious, and must 

 be very considerable in quantity, if we may judge from the calibre of the 

 mesenteric arteries, and from the extent of the internal surface of the in- 

 testines. It is, however, scarcely possible, that this exhalation should 

 amount to eight pounds in twenty-four hours, according to Haller's cal- 

 culation, who, as we shall observe, when we treat of the secretions, has 

 generally over-rated their amount. 



The peristaltic contractions, by the assistance of which, the alimentary 

 mass is sent along the whole course of the small intestines, do not occur 

 in a regular and uninterrupted succession, from the stomach to the 

 coecum. This undulatory and vermicular motion manifests itself at once, 



tine is mortified, one would decide the more readily to leave an artificial anus, if one 

 could be sure that the gangrenous portion belonged to the latter intestine ; but of this 

 it is absolutely impossible to be certain. -.Star's Note. 



* See APPENDIX, Note O, for some remarks respecting 1 the mucous coat of the 

 digestive eaual, and the functions of" the small and large intestines Copland. 



