THE SMALL IXTESTiyE 967 



h^iirface of this portion of the bowel. It i.-; <>t" interest as 1)eing the seat of origin 

 oi a retroperitoneal hernia. 



The fold forming the fossa is the remains of the 'duodenal fold,' modified by 

 growth and disjilaeed by the ])roeess of unequal development in the intestinal eanal 

 (page 1003 and ligs. (iOo, (300). The jjoeket, or fossa, is of triangular outline, 

 with the base or orifiee upwards. Its apex extends below the last bend of the 

 duodenum (fig. 572). The capacity of the fossa varies. In -well-marked speci- 

 mens it will lodge the thumb up to the first joint. It is actually occupied \^y the 

 duodcno-jejunal junction or bend. Out of on(.' hundred Ijodies examined, I found 

 this fossa in forty-eight examjjlcs. 



Jejunum and ileum. — There is no unvarying method in the arrangement of 

 tlie individual coils of the small intestine. 



In the majority of adult bodies the small intestine is disposed in an irregularly 

 curved manner from left to right. The gut, starting from the duodenum, will first 

 occupy the contiguous parts of the left side of the epigastric and umbilical regions; 

 the coils then fill some part of the left hypochondriac and luml)ar regions; they 

 now commonly descend into the pelvis, reappearing in the left iliac quarter, and 

 then occupy, in order, the hypogastric, lower umbilical, right luml)ar, and right 

 iliac regions. Before reaching the last situation they commonly descend again into 

 the pelvis. 



In many instances no kind of methodical arrangement is apparent. The coils 

 of small intestine most usually found in the pelvis belong to the terminal part of 

 tlie ileum, and to that part of the intestine that has the longest mesentery — the 

 part, namely, that extends between two points, respectively six and eleven feet 

 from the end of the duodenum. In five out of one hundred cases examined, the 

 coils were arranged in an exactly reverse manner to that just described. 



The jejunum (jejunvs, empty). — The jejunum is the name given to the upper 

 two-fifths of the small intestine Ijelow' the duodenum. 



The term ileum (eUstv, to twist) is api:)lied to the last three-fifths of the l)owel. 

 The ileum ends at the ileo-cajcal valve. The coils formed by the jejunum and 

 ileum are ver\^ movable, are completely invested by peritoneum, and are supported 

 and attached to the posterior parietes by the extensive membrane known as the 

 mesentery. 



The intestine alters gradually in character from above dowuAvards. If a segment 

 from the middle of the jejunum be compared Avith a portion of the middle ileum, 

 tlie following differences would be noted. The diameter of the jejunum is about 

 an inch and a half, that of the ileum one and a quarter. The jejunum has 

 thicker walls, is more vascular, and is provided with a more complex mucous 

 membrane. 



Meckel's diverticulum, — From one to three feet from the end of the ileum 

 is sometimes seen a diverticulum, or l)lind tube or cord, coming off from the free 

 margin of the bowel. This is Meckel's diverticulum, and represents the remains 

 of the vitello-intestinal duct (page 994). 



The mesentery. — The mesentery extends from the end of the duodenum to the 

 ileo-ctecal junction. It envelopes and supports the ileum and jejunum. Its upper 

 or right layer is continuous with the under layer of the transverse meso-colon and 

 with tlie jieritoneum that invests the ascending colon. Its lower or left layer joins 

 with the serous membrane that encloses the descending colon and that forms the 

 sigmoid mesentery (fig. 5G1). 



The point at which the mesentery is attached above is on a level with the lower 

 l)order of the pancreas and just to the left of the vertebral bodies. From this point 

 the insertion of the mesentery follows an oblirpie line that runs downwards and to 

 the right, crossing the great vessels, and ending in some part of the iUac fossa (fig. 

 599). In the al)sence of an ascending meso-colon (the normal condition) the peri- 

 toneum that covers the ca?cum is reflected from tlie hinder surface of that part of 

 the bowel fm to the posterior parietes; at this reflexion the mesentery ends. If an 

 ascending meso-colon exi.«!ts, the mesentery terminates by joining it. The parietal 

 attachment of the mesentery measures, as a rule, about six inches ffig. 509). The 

 length of the mesentery from the spine to the intestine varies in dift'crent parts of 

 the canal; its average length ni;iv betaken ;is liefwecn eiL'lit and nine inches. It 



