THE JEJUNUM AND ILEUM 1289 



is no morphological line of distinction between the jejunum and ileum, and the 

 division is arbitrary; but at the same time it must be noted that the character of 

 the intestine gradually undergoes a change from the commencement of the jeju- 

 num to the termination of the ileum, so that a portion of the bowel taken from 

 these two situations would present characteristics and marked differences. These 

 are briefly as follows : 



Jejunum. Ileum. 



Calibre larger (H inches), smaller (1 inch). 



Wall thicker, heavier. thinner, lighter. 



Color red, more vascular. pale, less vascular. 



Valvulae conniventes . . prominent. smaller and fewer. 



Lymphoid tissue .... diffuse and few nodules. diffuse and many Peyer's patches. 



Villi numerous, short, and broad, fewer, slender, filiform. 



Intestinal glands .... more numerous. less numerous. 



The Jejunum (intestinum jejunum). The jejunum is wider, its diameter being 

 about one inch and a half (3.75 cm.), and is thicker, more vascular, and of a deeper 

 color than the ileum, so that a given length weighs more. Its valvulae conniventes 

 are large and thickly set and its villi are larger than in the ileum. The patches of 

 Peyer are almost absent in the upper part of the jejunum, and in the lower part 

 are less frequently found than in the ileum, and are smaller and tend to assume 

 a circular form. Brunner's glands are only found in the duodenum. By grasping 

 the jejunum between the finger and thumb the valvulae conniventes can be felt 

 through the walls of the gut; these being absent in the lower part of the ileum, 

 it is possible in this w r ay to distinguish the upper from the lower part of the small 

 intestine. 



The Ileum (intestinum ilewni). The ileum is narrower, its diameter being 

 one inch (2.5 cm.) or a little more, and its coats are thinner and less vascular 

 than those of the jejunum. It possesses but few valvulae conniventes, and they 

 are small and disappear entirely toward its lower end, but Peyer's patches are 

 larger and more numerous. The jejunum for the most part occupies the umbilical 

 and left iliac regions, while the ileum occupies chiefly the umbilical, hypogastric, 

 right iliac, and pelvic regions, and terminates in the right iliac fossa by opening 

 into the inner side of the commencement of the large intestine. The jejunum 

 and ileum are attached to the posterior abdominal wall by an extensive fold of 

 peritoneum, the mesentery (p. 1263), which allows the freest motion, so that each 

 coil can accommodate itself to changes in form and position. The mesentery is 

 fan-shaped; its posterior border or root, about six inches (15 cm.) in length, is 

 attached to the posterior abdominal w T all from the left side of the body of the 

 second lumbar vertebra to the right iliac fossa, crossing successively the third part 

 of the duodenum, the aorta, the inferior vena cava, the right ureter and the 

 right Psoas muscle (Fig. 988). Its breadth between its vertebral and intestinal 

 borders is about eight inches (20 cm.) from its commencement to its termination 

 at the intestine, and it is greater in the middle than at either end of the bowel. 

 According to Lockwood, it tends to increase in length as age advances. Between 

 the two layers of which it is composed are contained bloodvessels, nerves, lacteals, 

 and lymph nodes, together with a variable amount of fat. 



Meckel's Diverticulum (diverticulum ilei). This consists of a pouch which pro- 

 jects from the lower part of the ileum in about 2 per cent, of subjects. Its average 

 position is about three feet from the ileocolic junction, and its average length about 

 two inches. Its calibre is generally the same as that of the ileum. Sometimes 

 only a portion of the proximal end has a lumen and the balance of the structure 

 is impervious and shrunk to a fibrous cord. In other cases the diverticulum is 

 actually of greater diameter than the intestine. It usually is at a right angle 

 to the intestine, but may take almost any direction. Its blind extremity may be 

 unattached or may be connected with the abdominal wall or with some other 



