840 THE INTESTINE. 



duodenum is invested by the peritoneum on its anterior surface only, 

 the posterior surface being connected to the right kidney and the verte- 

 bral column by areolar tissue. In front is the transverse colon and meso- 

 colon, the upper layer of which is continuous with the peritoneal covering 

 of the duodenum. To the left is the head of the pancreas, which adapis 

 itself to the shape of the intestine on that side. The common bile-duct 

 descends behind the left border of this part of the duodenum, and, to- 

 gether with the pancreatic duct, which accompanies it for a short distance, 

 perforates 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 val- 

 vulse conniventes appear numerously ; and an eminence or papilla found 

 about four inches below the pylorus, on the inner and back part of tho 

 intestine, marks the situation of the common orifice of the biliary and pan- 

 creatic ducts. 



The third or transverse or oblique portion, somewhat the longest and nar- 

 rowest, beginning on the right of the third lumbar vertebra, crosses in front 

 of the second obliquely from right to left, and, continuing to ascend obliquely 

 for an inch or more, ends in the jejunum at the left side of the vertebral 

 column. It is placed immediately behind the root of the transverse meso- 

 colon, and the commencement of the mesentery, as has been already de- 

 scribed, and has the V( na cava inferior and the aorta behind it. At its 

 termination it forms an abrupt angle with the commencement of the jeju- 

 num. This is due to its being maintained, at that point, in its position, by 

 a strong fibrous band descending from the left eras of the diaphragm and 

 the tissue round the coeliac axis. According to Treitz, muscular fibres 

 come from both these sources to this part 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 baud alluded to, its terminal extremity maintains a uniform position. 

 Close to this point the superior mesenteric vessels pass from beneath the 

 pancreas to enter the mesentery on the surface of the duodenum. 



JEJUNUM AND ILEUM. The jejunum, originally so called from its having 

 been supposed to be empty after death, follows the duodenum, and in- 

 cludes the upper two-fifths of the remainder of the small intestine, while 

 the succeeding three-fifths constitute the ileum, so named from its nume- 

 rous coils or convolutions. Both the jejunum and the ileum are attached 

 and supported by the mesentery. The convolutions of the jejunum are 

 situated in part of the umbilical and left iliac regions of the abdomen ; 

 while the ileum occupies part of the umbilical and right iliac regions, 

 together with the hypogastric, and descends into the pelvis, from which its 

 lower end, supported by the mesentery, which is heie very short, ascends 

 obliquely to the right and somewhat backwards, over the corresponding 

 psoas muscle, and ends in the right iliac fossa, by opening into the inner 

 side of the commencement of the large intestine. There is no defined 

 limit between the jejunum and the ileum, but the character of the intes- 

 tine gradually changes from its upper to its lower end, so that portions 

 of the two intestines, remote from each other, present certain well- 

 marked differences of structure, which may be here enumerated. Thus, 

 the jejunum is wider, and its coats are thicker ; it is more vascular, and 

 therefore it has a deeper colour ; its valvulse conniventes are long, wide, 

 and numerous ; its villi are well developed ; and the patches of Peyer's 

 glands are smaller, less frequent, and sometimes confined to its lower 

 part. The ileum, on the other hand, is narrower ; its coats are thin- 



