THE LARGE INTESTINE. 1025 
measured along the gut, the greatest distance being 12 feet, and the smallest 6 inches. In 
52 specimens the average length was 2°] inches, the longest being 52 inches, the shortest 4 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. (The foregoing results have been compiled from the reports of The Collective 
Investigation of the Anatomical Society of Great Britain and Ireland—L. J. Mitchell, Kelynack, 
Rogie, and Augier.) 
Vessels and Nerves of the Jejunum and Ileum.—The arteries for both the jejunum and 
ileum—the vasa intestini tenuis—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 ter- 
minal branches (Fig. 683) 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 glands 
of Lieberktthn, whilst others pass to the villi The veins are similarly disposed, and the 
blood trom 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. 
he lymphatics of the small intestine (known as lacteals) begin in the villi, and also as 
lymphatic sinuses surrounding the bases of the solitary glands; a large plexus is formed in the 
sulmucosa, 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 one, or a few, 
intestinal lymphatic trunks, which open into the receptaculum chyli. 
The nerves come from the solar plexus, through the superior mesenteric, which latter 
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—that of Auerbach in the muscular coat, and the plexus of Meissner in the sub- 
mucosa. 
Structure.—The serous coat is complete in all parts of the jejunum and ileum. 
The muscular coat is much thicker in the jejunum, and grows gradually thinner as it 
is traced down along the ileum. The submucosa contains the bases of the solitary glands 
(Fig. 684), but otherwise calls for no special remark. The mucous coat is thicker and 
redder above, in the jejunum, thinner and paler in the ileum. It is covered throughout 
by villi, which are said to be shorter and broader in the jejunum, longer and narrower 
in the ileum. In its whole extent it is closely beset with Lieberkiihn’s follicles, and 
numerous solitary glands are seen projecting on its surface. Peyer's patches are 
particularly large and numerous in the ileum; they are fewer, smaller, and usually 
circular, in the jejunum. Finally, the mucous membrane forms valvule conniventes, 
which are largest in the jejunum; they are smaller and fewer in the upper part of the 
ileum, and usually disappear a little below its middle. 
THE LARGE INTESTINE. 
The ileum is succeeded by the large intestine (intestinum crassum), which 
begins on the right side, some 24 inches below the ileo-czecal junction, and com- 
prises the following parts :— 
1. The cecum, a wide short cul-de-sac, consisting of the portion of the large 
bowel below the ileo-cecal junction. It lies in the right iliac region, and from 
its inner and back part a worm-shaped outgrowth, the vermiform process, is pro- 
longed (Fig. 691). 
2. The ascending colon extends from the cecum, up in the right side of the 
abdomen, to the liver: here the gut bends to the left, forming the hepatic flexure, 
which connects the ascending colon to the transverse colon. 
3. The transverse colon is a long loop of intestine which arches across the 
abdominal cavity in an irregular manner. It ends at the lower extremity of the 
spleen, where it turns downward, forming the splenic flexure, and passes into the 
descending colon. 
4. The descending colon runs down on the left side, from the splenic flexure 
to the iliac crest. 
5. The iliac colon extends from the crest of the ilium to the brim of the pelvis, 
where it is succeeded by the pelvic colon. 
6. The pelvic colon is a large loop of intestine which is usually found in the 
pelvis. The iliac and pelvic portions of the colon taken together are commonly 
described as the sigmoid flewure of the colon. 
