472 ABDOMEN 



great omentum. The jejunum begins where the duodenum 

 ends, viz. on the left side of the body of the second lumbar 

 vertebra ; and the ileum ends in the lower part of the right 

 iliac region by joining the caecum or the commencement of 

 the large intestine. The subdivision of the small intestine is 

 of the most arbitrary kind. After mapping off the duodenum 

 it is customary for anatomists to .look upon the upper two- 

 fifths of the remainder as being jejunum, and the lower three- 

 fifths as being ileum. There is no hard-and-fast line of 

 demarcation between the lower two divisions the one passes 

 insensibly into the other ; and, as the chief distinction is 

 to be found by an examination of the interior of the tube, the 

 student will not in the meantime see much difference between 

 them. 



To expose the commencement of the jejunum, the greater 

 omentum with the enclosed transverse colon should be thrown 

 upwards over the lower margin of the thoracic wall. The 

 coils of the small intestine should then be drawn over to the 

 right. The junction between the duodenum and the jejunum 

 will now be seen on the left side of the vertebral column, at 

 the level of the second lumbar vertebra. The termination of 

 the duodenum is fixed, partly by its relation to the peritoneum 

 and partly by the suspensory muscle of Treitz which will be 

 described later (p. 500), and the commencement of the 

 jejunum bends suddenly forwards and downwards upon it, 

 forming the duodeno-jejunal flexure. To bring the termination 

 of the ileum into view, the coils of the intestine should be 

 turned over to the left. The terminal part of the ileum, 

 which almost invariably lies in the pelvis, has no great latitude 

 of movement. It passes upwards across the iliac vessels and 

 upon the psoas muscle, to join the caecum at the level of the 

 intertubercular plane, and close to the right lateral plane. 



The coils formed by the jejunum and ileum are suspended 

 from the posterior wall of the abdomen by a wide fold of 

 peritoneum, called the mesentery. They are thus freely 

 movable within the cavity. Owing to the manner in which 

 the mesentery is attached to the posterior wall of the abdomen 

 (Fig. 183, p. 475), they tend to lie more in the left than in 

 the right portion of the cavity, and they occupy the umbilical, 

 hypogastric, lumbar, and iliac regions, filling up the greater 

 part of the abdominal cavity below the transverse colon and 

 its mesentery. A variable number of coils extend downwards 



