THE ABDOMEN, INTERIOR. 499 



The Small Intestine. Figs. 96 to 100. 



The first two-fifths of the intestine below the duodenum 

 is called the jejunum, the remaining three-fifths, the ileum. 

 The coils of the small intestine fill in the space left by the 

 arching colon at the sides and above, and the pelvic viscera 

 below. They are attached to the posterior abdominal wall 

 by the mesentery, a double layer of peritoneum, which 

 reaches from the left side of the second lumbar vertebra to 

 the right iliac fossa, a distance of four to six inches. The 

 mesentery is about eight or nine inches in width, and in 

 length along its intestinal border equals the jejunum and 

 ileum. Between the layers of the mesentery the superior 

 mesenteric artery ramifies. Sometimes a remnant of the 

 vitello-intestinal duct is found on the outer border of the 

 ileum at a distance of from one to three feet from the ileo- 

 caecal valve ; if present it is called Meckel's diverticulum. 

 When existing it may be a menace to the individual on ac- 

 count of forming adhesions with some other part of the 

 abdomen, thus forming a band or bridge over or under 

 which a portion of the intestine might become constricted. 

 In the normal subject it will be seen that the mesentery is 

 just short enough to keep the margin of the intestine from 

 engaging in the abdominal rings or femoral opening, con- 

 sequently in hernia the mesentery must be abnormally 

 elongated congenitally or by acquisition. 



The ileum joins the large intestine in the right inguinal 

 region, at right angles to the larger gut, and from two to 

 three inches from its lower blind extremity. 



The small intestine opens by a valvular orifice, the ileo- 

 caecal valve, into the larger. This opening is behind a 

 line joining the anterior superior iliac spine and the um- 

 bilicus, and at a distance of three inches from the first 

 point. 



