1652 HUMAN ANATOMY. 



remainder is disposed vertically, occupying^ the lower part of the umbilical region 

 and the pelvis, and extending on the right as far as the large intestine will allow. 

 The vertical arrangement of this portion is generally less striking than the trans- 

 verse disposition of the preceding. The end of the ileum rises from the pelvis into 

 the right iliac fossa. There are, of course, frequent deviations from the above plan 

 of arrangement of the folds. It is easy to see that the appearance at the surface of 

 some that are usually deep would obscure the plan. It is worth noting that adjacent 

 folds should never be assumed to be continuous. 



Blood-Vessels. — The arteries of the jejuno-ileum are branches of the 

 superior mesenteric, which enters the mesentery below the pancreas. The vessels 

 for the gut are straight ones arising from the arterial arches. In the upper part 

 they are from 4-5 cm. long, 3 cm. in the middle, and very small at the end of the 

 ileum. They run without anastomoses to the edge of the gut, where they break up 

 into bunches of slightly dii'erging branches. All of these usually go to one side of 

 the gut, each alternate vessel taking a different side, although sometimes a vessel 

 may send branches to both sides. Anastomoses in the walls of the gut between 

 the branches of neighboring arteries are not numerous, and occur only between 

 very fine vessels, except opposite the mesentery, where vessels of the different sides 

 meet. The distribution of the veins is essentially the same. 



The lymphatics, large and numerous, empty into the mesenteric nodes, 

 which they connect. These lymph-nodes vary in number from one to two hundred, 

 the largest lying near the root of the mesentery, from which position they grow 

 smaller as they approach the free edge. There are no nodes, however, between the gut 

 and the last vascular arch, unless, perhaps, near the very end of the small intestine. 



The nerves of the entire small intestine are from the solar plexus. They 

 receive many cerebro-spinal fibres through the splanchnics. 



Meckel's Diverticulum. — This is a protrusion from the ileum, shaped like 

 the finger of a glove, and found in some 2 per cent. It is the remnant of the \'itel- 

 line duct, which at an early stage connects the gut with the yolk-sac. It springs 

 most frequently from the free border of the bowel, sometimes, however, from the 

 side, and, as a rule, but not invariably, is composed of all the intestinal coats. Its 

 usual position is within i m. (on an average, 82 cm.) of the caecum. The diameter 

 of the diverticulum is usually that of the gut, but it may be less and associated with 

 a conical form. The length varies from 2.5 cm. or less to 17.5 cm. (7 in. ), although 

 ordinarily between 2.5 and 7.5 cm. (i and 3 in.). As a rule, its end is free, but 

 often a delicate band extends from its apex to the umbilicus or to some of the contents 

 of the abdomen, generally the mesentery.^ The occasional diverticula, found especially 

 in the duodenum, are probably pathological and do not include the muscular coat. 



PRACTICAL CONSIDERATIONS : THE SMALL INTESTINE. 



I. The Peritoneal Coat. — This is complete below the duodenum except at the 

 mesenteric aspect, where the two layers of peritoneum diverge for about 8 mm. ( ^^ in. ). 

 The jejuno-ileum is therefore practically an intraperitoneal, and not merely an intra-ab- 

 dominal, viscus, although, of course, really outside the peritoneal sac. Inflammation 

 of this portion of the general peritoneum is more apt to be acute, to spread rapidly, 

 and to be attended by serious or fatal results than is that of any other portion. Such 

 infection is frequent on account of the great length of the small intestine, its exposure 

 to trauma, the thinness of its muscular walls, the variety and number of the lesions 

 of its mucosa, its close relation to all the intra-abdominal viscera, and its consequent 

 participation in their injuries and diseases. Direct transmission of infection from 

 within outward is favored by the relatively intimate relation between the peritoneal 

 and muscular coats, the subserous areolar tissue being much scantier and containing 

 much less fat than that intervening between the parietal peritoneum and the fasciae 

 and muscles of the abdominal wall. The extent and fatality of peritoneal inflam- 

 mation result from the facility with which it spreads by both continuity and contiguity, 

 and from the fact that, cceteris paribjis, its toxic products are proportionate in amount 

 to the area involved. The association of the spinal and sympathetic nerves in the 



^ Lamb : American Journal of the Medical Sciences, 1893. 



