110 



in several points of the length of the tube, whose curvatures straighten 

 themselves at intervals. In this action, the intestinal curves are decom- 

 posed into a great number of short straight lines which meet, so as to 

 form obtuse angles. The peristaltic motion which affects the muscular 

 fibres of the intestines, is caused by the irritation of the alimentary sub- 

 stance on the sentient parietes of the canal along which it descends, to- 

 wards the great intestines. The jejunum and the ileum, covered by the 

 peritoneum, except at the part which connects them to the mesentery, at 

 the time of dilatation, separate the two peritoneal laminae, forming the 

 mesentery. They occupy the space between the branches of the mesen- 

 teric vessels, whose last division is always at some distance from the ad- 

 hering edge of the intestine. If this division of the vessels had taken 

 place, nearer to the union of the intestine and mesentery, the intestinal 

 canal would not have admitted of dilatation, without stretching the ves- 

 sels situated at the angle of separation. It is likewise observed, that in 

 the portions of the digestive tube which are most susceptible of dilata- 

 tion, the last vascular divisions are most distant. Hence the left gastro- 

 epiploic artery is always at a greater distance from the great curvature of 

 the stomach, than the right, a circumstance of which no anatomist has 

 hitherto taken notice. 



XXIX. Of Digestion in the Great Intestines. The alimentary mass, after 

 it has parted with nearly the whole of its nutritive particles, passes from 

 the ileum into the coecum ; it then is received into the great intestines, 

 which aie more spacious, though shorter, than the small, forming scarce- 

 ly, a fifth of the whole length of the digestive tube. 



A musculo-membranous valvular ring is placed at the oblique insertion 

 of the ileum into the first of the great intestines. This valve, called after 

 Eustachius or Bauhinus, who are considered as its discoverers, though 

 the merit of the discovery belongs to Fallopius, is formed of two semi- 

 circular segements, the right edge of which is free, and floats towards the 

 cavity of the coecum. The more the parietes of that intestine are dis- 

 tended by the substances which it contains, the greater is the difficulty to 

 the retrograde flow of such substances, for under those circumstances, 

 the two extremities of the valve are at a distance from each other, and 

 its edges, which are free, close on each other, like those of a button-hole 

 whose angles are drawn in opposite directions; besides, the muscular 

 fibres which enter into its structure, render it capable of exerting con- 

 striction. It is, therefore, calculated to permit the ready flow of matter, 

 from the ileum into the coecum, and forcibly prevent their return in- 

 to the small intestines. There are facts which lead to a belief, that its 

 resistance is sometimes overcome, and that a clyster, thrown in with 

 violence, would force the valve, and be thrown up by vomiting. The 

 great intestines may be considered as a kind of reservoir destined to 

 contain, for a certain time, the excrementitious residue of our solid ali- 

 ments, so as to save us the disgusting inconvenience of constantly part- 

 ing with it. 



As the peritoneum does not wholly cover the great intestines, they 

 are capable of considerable dUitation, and of extending into the cellular 

 substance which connects them to the posterior part of the abdomen. 

 Their muscular coat which, in a manner, is the base of the intestinal 

 tube, does not consist throughout, of circular and longitudinal fibres. The 

 latter, collected into fasciculi, form three narrow bands, in the intervals 

 of which, the parietes of the gut are exceedingly weakened, and conse- 



