472 THE DIGESTIVE APPARATUS IN MAMMALIA. 



Course and Relations. — The small intestine commences at the right cul-de-sac 

 of the stomach, from which it is separated by the pyloric constriction. At its 

 origin it presents a dilatation which, in form, closely simulates a small stomach, 

 the curvatures of which are the inverse of those of the proper stomach. Placed 

 at the posterior face of the liver, this expansion, or head, of the small intestine 

 begins the narrower portion, which at first is directed forward, then bends 

 suddenly backward — thus forming a loop investing the base of the cacum on 

 the right side ; then it is carried to the left in crossing, transversely, the sub- 

 lumbar region, behind the. great mesenteric artery ; here it is joined to the 

 origin of the floating colon by a very short serous frasnum. It then reaches the 

 left flank, where it is lodged, and where it forms numerous folds that are freely 

 suspended in the abdominal cavity among the convolutions of the small colon. 

 The terminal portion of this conduit, which is easily recognized hj the greater 

 thickness of its walls and its smaller diameter, disengages itself from these 

 convolutions to return to the right, and opens into the concavity of the caecum, 

 below, and a little to the inside of, the point where the large colon has its 

 commencement. 



In the language of the schools, this terminal portion is named the ileum 

 (eiXetv, " to twist ") ; the part which is suspended in the left flank, and which forms 

 the principal mass of the intestine, is designated the jejunum {jejunas, " empty ") ; 

 and the curvature formed by this viscus at its origin, from the pylorus to the 

 great mesenteric artery, is termed the duodenum (twelve fingers' breadth). 



This classical division is, however, altogether arbitrary, and scarcely deserves 

 to be retained. It would be better to divide the intestine into a Jixed or 

 duode7ial, a,nd a. free or Jloating portion. 



Mode of attachment. — The small intestine is maintained in its position, at its 

 extremities, by the stomach and the ctecum. But its principal means of fixation 

 consists in a vast peritoneal fold, which, from its use, is named the mesentery 

 (jjLeaov, evrepov, " mediate " or " middle "). 



This serous layer presents a very narrow anterior part which sustains the 

 duodenum, and fixes it in such a manner as to prevent its experiencing any 

 considerable displacement. Continuous, in front, with the gastro-hepatic 

 omentum, this portion of the mesentery is successively detached from the base 

 of the liver, the inferior aspect of the right kidney, or even from the external 

 contour of the base of the ctecum, and, lastly, from the sublumbar region, to 

 be soon confounded with the principal mesentery. This becomes wider as it 

 approaches the enseal extremity, and arises, as from a centre, from the outline 

 of the great mesenteric artery, to spread in every direction, and is inserted into 

 the small curvature of the floating portion of the viscus. The great length of 

 this insertion causes it to become extended in a spiral or screw-like manner, 

 around its point of origin. It may be remarked that the terminal extremity of 

 the intestine is retained between the two serous layers of the mesentery, to a 

 certain distance from its free border. This peritoneal fold consequently forms 

 at this point— at the side opposite to its insertion into the intestinal tube — a 

 particular fr^enum, which is observed to be carried to the anterior face of the 

 caecum. 



Interior.— The interior of the small intestine shows longitudinal folds, which 

 are effaced by distension, except towards the origin of the duodenal portion^ 

 Those met with in this situation possess all the characters of the ralvulce 

 connivenfes {valves of Kerkring) in Man ; they resist traction on the intestinal 



