The Intestines. 221 



the index finger, and may form a sac for a retro-peritoneal 

 hernia. 



Jejunum and Ileum. The name jejunum is applied to 

 the upper two-fifths of the small intestine below the duo- 

 denum, while ileum is applied to the remaining three-fifths, 

 and though, when a portion of the jejunum near its begin- 

 ning is examined, it will be seen to differ in some respects 

 from the ileum, especially near its termination, yet there 

 is no point where one can say the jejunum ends and the 

 ileum begins. 



The Mesentery. The constant peristaltic move- 

 ment and the changing pressure from the action of the ab- 

 dominal muscles, and from the position, etc., of the body, ne- 

 cessitate that the bowel should be so supported, as to per- 

 mit the freest gliding of one part over the other, and for 

 this purpose we have the mesentery. The mesentery is 

 formed by two layers of the peritoneum, between which 

 pass the blood vessels, lymphatics, etc., for the intestine, 

 and it supports the bowel by connecting it to the vertebral 

 column. As the mesentery approaches the bowel, it 

 splits so as to enclose the latter, the separation beginning 

 about two-thirds of an inch from the surface of the bowel, 

 and the base of the triangular space thus exposed is 

 formed by the musclar coat of the intestine and is about 

 five-sixteenths of an inch in width. The length of the 

 mesentery varies, the average being about eight inches, 

 although that portion of the intestine between six and 

 eleven feet from the duodenum has, as a rule, a mesentery 

 longer than the average. The length of its vertebral at- 

 tachment is about six inches and extends from the left side 

 of the second lumbar vertebra, obliquely across the verte- 

 bral column, to the right iliac fossa, and, at its termina- 

 tion in this fossa, it is very short, so that, next to the duo- 

 denum, this lowest portion of the ileum is the most fixed 



