370 THE SMALL INTESTINE. 



the shape of the intestine on that side, and, according to Terson, some 

 of the longitudinal mnscular fibres of the gut are intercalated amongst 

 the contiguous lobules of the gland. The common bile-duct descends 

 behind the left border of this part of the duodenum, and, together with 

 the pancreatic duct, which accompanies it for a short distance, per- 

 forates the coats of the intestine obliquely near the lower part of its 

 left or concave border. In the interior of this part of the intestine the 

 valvulas conniventes appear numerously ; and a downwardly projecting, 

 papillary eminence of the mucous membrane is found immediately 

 IdcIow one of these, about four inches below the pylorus, on the inner 

 and back ]")ai't of the intestine, at the apex of which is seen the common 

 orifice of the biliary and pancreatic ducts. 



The third, transverse or oblique portion {cl'), somewhat the longest 

 and narrowest, beginning on the right of the third laminar vertebra, 

 crosses in front of the second obliquely from right to left. It makes its 

 appearance below the transverse mesocolon, and, continuing to ascend for 

 an inch or more, ends in the jejunum (/) at the left side of the vertebral 

 column, immediately behind the root of the transverse mesocolon, and 

 the commencement of the mesentery, and has the vena cava inferior and 

 the aorta behind it, while in front of it the superior mesenteric vessels {m) 

 pass from beneath the pancreas to enter the mesentery. 



At its temiination the duodenum foiiiis an abraiit angle with the commence- 

 ment of the jejunum. Tliis is due to its being maintained, at that point, in 

 its position, by a strong fibrous band descending from the left cnas of the dia- 

 phragm and the tissue around the coeliac axis. According to Treitz. muscular 

 fibres come from both these soui'ces to this pai-t of the duodenum. In subjects 

 in which the intestines are large and dilated, the curve of the duodenum may- 

 descend to the level of the iliac crest, but, owing to the support given by the 

 band alluded to, its tenniaal extremity maintains a unifoiin position. 



Jejunum and Ileum. — The jejunum, originally so called from its 

 having been supposed to be empty after death, follows the duodenum, 

 and includes the upper two-fifths of the remainder of the small intes- 

 tine, while the succeeding three-fifths constitute the ileum, so named 

 from its numerous coils or convolutions. Both the jejunum and the 

 ileum are attached and supported by an extensive fold of peritoneum 

 termed the mesentery. The mesentery of the small intestine, although 

 greatly frilled out in front to correspond in length with the jejunum 

 and ileum to which it affords support, is attached posteriorly by a very 

 short border which extends fi'om the level of attachment of the trans- 

 verse colon immediately to the left of the middle line, directly down to 

 the right iliac fossa, where the ileum falls into the caecum. At its 

 widest part the length of the mesentery is from four to six inches 

 between its vertebral and its intestinal border. Between the two layers 

 of peritoneum of which it consists are placed, besides some fat, numerous 

 branches of the superior mesenteric artery and vein, together with 

 nerves, lacteal vessels, and mesenteric glands. The convolutions of the 

 jejunum are situated iu part of the umbilical and left iliac regions of 

 the abdomen ; while the ileum occupies part of the umbilical and right 

 iliac regions, together Avith the hypogastric, and descends into the 

 pelvis, from which its lower end, supported by the mesentery, which is 

 here very short, ascends obliquely to the right and somewhat back- 

 wards, over the corresponding psoas muscle, and ends in the right 

 iliac fossa, by opening into the inner side of the commencement of the 



