1210 THE DIGESTIVE SYSTEM. 



The villi are also said to be shorter and broader in the jejunum, more slender 

 and filiform in the ileum (Kauber). 



The terminal portion of the ileum, after crossing the margin of the superior 

 aperture of the pelvis minor, runs upwards, and also slightly backwards and to the 

 right, in close contact with the csecum, until the ileo-ccecal orifice is reached. 



Diverticulum Ilei (O.T. Meckel's Diverticulum). This is a short finger-like protrusion 

 which is found springing from the lower part of the ileum in a little over 2 per cent, of the bodies 

 examined. It is usually about 2 inches long, and of the same width as the intestine from which 

 it comes off. Most commonly it is found about 2| feet from the valvula coli, and opposite 

 the original termination of the superior mesenteric artery. As a rule, its end is free ; but 

 occasionally it is adherent either to the abdominal wall, the adjacent viscera, or the mesentery, 

 and in such cases it may be the cause of strangulation of the intestine. 



The diverticulum is due to the persistence of the proximal portion of the vitelline (or vitello- 

 intestinal) duct, which connects the primitive intestine of the embryo with the yolk sac. In 

 shape it may be cylindrical, conical, or cord-like, and it may present secondary diverticula near 

 its tip. It arises most frequently from the free border of the intestine, but it sometimes conies 

 off from the side. It runs at right angles to the gut most commonly, but it may assume any 

 direction, and it is often provided with a mesentery. In 3302 bodies specially examined with 

 reference to its existence, it was present in 73, or 2'2 per cent., and it appeared to be more common 

 in the male than in the female. In 59 out of the 73 cases its position with reference to the end 

 of the ileum was examined : its average distance from the ileo-csecal valve was 321 inches 

 measured along the gut, the greatest distance being 12 feet, and the smallest 6 inches. In 

 52 specimens the average length was 2'1 inches, the longest being 5j inches, the shortest ^ inch. 

 The diameter usually equals that of the intestine from which it springs ; but occasionally it 

 is cord -like, and pervious only for a short way ; on the other hand, it may attain a diameter of 

 3| inches. 



Vessels and Nerves of the Jejunum and Ileum. The arteries for both the jejunum and 

 ileum the jejunal and ileal come from the superior mesenteric, and are contained between 

 the two layers of the mesentery. After breaking up and forming three tiers of arches, the terminal 

 branches (Fig. 772, p. 931) reach the intestine, where they bifurcate, giving a branch to each side 

 of the gut. These latter run transversely round the intestines, at first under the peritoneal coat ; 

 soon, however, they pierce the muscular coat and form a plexus in the submucosa, from which 

 numerous branches pass to the mucous membrane, where some form plexuses around the 

 intestinal glands whilst others pass to the villi. The veins are similarly disposed, and the 

 blood from the whole of the small intestine beyond the duodenum is returned by the superior 

 mesenteric vein, which joins with the splenic to form the portal vein. 



The lymph vessels of the small intestine (known as lacteals) begin in the villi, and also 

 as lymph sinuses surrounding the bases of the solitary nodules ; a large plexus is formed in the 

 submucosa, a second between the two layers of the muscular coat, and a third beneath the 

 peritoneum. The vessels from all these pass up in the mesentery, being connected on the way 

 with the numerous (from 40 to 150) mesenteric glands, and finally unite to form the truncus 

 intestinalis, which opens into the cisterna chyli. 



The nerves come from the coeliac plexus, through the superior mesenteric plexus, which 

 accompanies the superior mesenteric artery between the layers of the mesentery, and thus 

 reaches the intestine. Some of the fibres are derived ultimately from the right vagus. The 

 nerve-fibres are non-medullated, and form, as in other parts of the canal, two gangliated 

 plexuses the my enteric in the muscular coat, and the submucosal in the submucosa. 



Structure. The tunica serosa is complete in all parts of the jejunum and ileum. 

 The tunica muscularis is thicker in the jejunum, and grows gradually thinner as it is 

 traced down along the ileum. The tela submucosa contains the bases of the solitary 

 nodules (Fig. 929), but otherwise calls for no special remark. The tunica mucosa is thicker 

 and redder above in the jejunum, thinner and paler in the ileum. It is covered through- 

 out by villi intestinal es, which are shorter and broader in the jejunum, longer and narrower 

 in the ileum. In its whole extent it is closely set with intestinal glands, and numerous 

 solitary nodules are seen projecting on its surface. Aggregated lymph nodules are 

 particularly large and numerous in the ileum ; they are fewer, smaller, and usually 

 circular in the jejunum. Finally, the mucous membrane forms plicae circulares, which 

 are much more prominent in the jejunum ; they are smaller and fewer in the superior 

 part of the ileum, and usually disappear a little below its middle. 



INTESTINUM CEASSUM. 



The ileum is succeeded by the intestinum crassum (large intestine), which 

 begins on the right side, some 2J inches below the ileo-csecal junction, and com- 

 prises the following parts : 



