1170 SPLANCHNOLOGY 



are also behind it. At its medial side is the head of the pancreas, and the common 

 bile duct; to its lateral side is the right colic flexure. The common bile duct and 

 the pancreatic duct together perforate the medial side of this portion of the intestine 

 obliquely (Figs. 1057 and 1100), some 7 to 10 cm. below the pylorus; the accessory 

 pancreatic duct sometimes pierces it about 2 cm. above and slightly ?h front of these. 



The horizontal portion (pars horizontalis; third or preaortic or transverse portion) is 

 from 5 to 7.5 cm. long. It begins at the right side of the upper border of the fourth 

 lumbar vertebra and passes from right to left, with a slight inclination upward, 

 in front of the great vessels and crura of the diaphragm, and ends in the ascending 

 portion in front of the abdominal aorta. It is crossed by the superior mesenteric 

 vessels and the mesentery. Its front surface is covered by peritoneum, except 

 near the middle line, where it is crossed by the superior mesenteric vessels. Its 

 posterior surface is uncovered by peritoneum, except toward its left extremity, 

 where the posterior layer of the mesentery may sometimes be found covering it 

 to a variable extent. This surface rests upon the right cms of the diaphragm, 

 the inferior vena cava, and the aorta. The upper surface is in relation with the 

 head of the pancreas. 



The ascending portion (pars ascendens; fourth portion) of the duodenum is about 

 2.5 cm long. It ascends on the left side of the aorta, as far as the level of the upper 

 border of the second lumbar vertebra, where it turns abruptly forward to become 

 the jejunum, forming the duodenojejunal flexure. It lies in front of the left Psoas 

 major and left renal vessels, and is covered in front, and partly at the sides, by 

 peritoneum continuous with the left portion of the mesentery. 



The superior part of the duodenum, as stated above, is somewhat movable, 

 but the rest is practically fixed, and is bound down to neighboring viscera and the 

 posterior abdominal wall by the peritoneum. In addition to this, the ascending 

 part of the duodenum and the duodenojejunal flexure are fixed by a structure 

 to which the name of Musculus suspensorius duodeni has been given. This structure 

 commences in the connective tissue around the celiac artery and left crus of the 

 diaphragm, and passes downward to be inserted into the superior border of the 

 duodenojejunal curve and a part of the ascending duodenum, and from this it is 

 continued into the mesentery. It possesses, according to Treitz, plain muscular 

 fibers mixed with the fibrous tissue of which it is principally made up. It is of 

 little importance as a muscle, but acts as a suspensory ligament. 



Vessels and Nerves. The arteries supplying the duodenum are the right gastric and superior 

 pancreaticoduodenal branches of the hepatic, and the inferior pancreaticoduodenal branch of 

 the superior mesenteric. The veins end in the lienal and superior mesenteric. The nerves are 

 derived from the coeliac plexus. 



Jejunum and Ileum. The remainder of the small intestine from the end of the 

 duodenum is named jejunum and ileum; the former term being given to the upper 

 two-fifths and the latter to the lower three-fifths. There is no morphological line 

 of distinction between the two, and the division is arbitrary; but at the same time 

 the character of the intestine gradually undergoes a change from the commence- 

 ment of the jejunum to the end of the ileum, so that a portion of the bowel taken 

 from these two situations would present characteristic and marked differences. 

 These are briefly as follows: 



The Jejunum (intestinum jejunum) is wider, its diameter being about 4 cm., 

 and is thicker, more vascular, and of a deeper color than the ileum, so that a given 

 length weighs more. The circular folds (valvulce conniventes) of its mucous mem- 

 brane are large and thickly set, and its villi are larger than in the ileum. The aggre- 

 gated lymph nodules are almost absent in the upper part of the jejunum, and in 

 the lower part are less frequently found than in the ileum, and are smaller and tend 

 to assume a circular form. By grasping the jejunum between the finger and thumb 

 the circular folds can be felt through the walls of the gut; these being absent in 



