THE INTESTINAL CANAL. 



1019 



FIG. 637. Muscle of Treitz. The large intes- 

 tine, jejunum, mesentery, and pancreas are 

 removed. (After Treitz in Jonnesco.) D. In- 

 ferior surface of diaphragm. E. Posterior sur- 

 face of stomach. F. Liver. Ls. Spigelian lobe. 

 Vb. Gall-bladder and duct. VCI. Vena cava. 

 Ac. Codiac axis. PC. Coeliac plexus. ADJ. 

 Duodeno-jejunal angle. Ms. Muscle of Treitz. 

 MB. Original mesoduodenum. 



Treitz indicates a cellular membrane (Fig. 637) stretching between the supe- 

 rior mesenteric artery on one side, the pylorus, duodeno-jejunal angle, and con- 

 cavity of the duodenum on the other, which forms a floor to the posterior surface 

 if the pancreas and represents the foetal mes- 

 entery of the duodenum. He says on account 

 of its'tenuity it is unable to offer any fixation. 



Such are the means of fixation in general. 

 The duodenal ring is fixed in all its length, 

 but unequally ; it is suspended by two fixed 

 extremities. Its superior hepatic angle is 

 fixed by the total of organs attached to the 

 liver and by the thick cellular tissue which 

 fastens it to the inferior vena cava. There 

 are also the structures forming the hepatic 

 pedicle, artery, duct, and portal vein, all sur- 

 rounded by fibre-nervous layers and all united 

 into one by the serous membrane forming the 

 lig. hepato-duodenale. Finally, the fibro-ner- 

 vous tissue contained in the lig. cystico- 

 duodenale serves to render the first part of 

 the duodenum solid to the liver. The liver 

 is fixed, not by peritoneal folds, as is com- 

 monly said, but by a thick cellular tissue and 

 numerous subhepatic veins emptying into the 

 inferior cava nailed, so to speak, to the pos- 

 terior abdominal wall. By such attachment 

 to the vena cava and liver, the superior angle 

 is secure. 



The duodeno-jejunal angle is fixed by the 

 muscle and ligament of Treitz. When this angle penetrates the thickness of the 

 transverse mesocolon its fixation is still more assured. The branches of the supe- 

 rior mesenteric artery given to this angle reinforce the support. More than the 

 ends of the duodenal arch must be supported or its lower part would separate 

 from the posterior abdominal wall and come forward on a hinge-movement. As 

 long as nothing presses this part of the duodenum backward this forward move- 

 ment does occur, as in early human embryos or in case of a mesoduodenum, as in 

 many animals. 



Normally the adult human duodenum cannot separate from the posterior wall, 

 owing to many agencies which come, in turn, to hold it down. 



The descending duodenum is fixed to the inferior vena cava and right kid- 

 ney by thick cellular tissue. This is further strengthened by the hepatic 

 flexure and transverse colon, which apply themselves directly to the kidney and 

 duodenum. 



The pre-aortic portion is fixed by two agents (a) by fibrous tissue between it 

 and the aorta and vena cava inferior : (b) by the superior mesenteric artery sur- 

 rounded by its fibro-nervous tissue, which forms the root of the mesentery and 

 presses this part of the duodenum down upon the aorta. So the mesenteric 

 artery and aorta, passing one behind the other, constitute a sort of vascular 

 press, lessening the calibre to what may be called the isthmus of the duode- 

 num. 



The ascending portion is much less fixed than any other part to the posterior 

 wall and left kidney. It is easily displaced from left to right, and peritoneal 

 covering is its sole agency of fixation. 



Rsum$. The duodenal ring is fixed against the posterior abdominal Avail, 

 or, better, against the fixed organs which cover it. This fixity is assured in 

 part by the vascular system and by the fibro-nervous layers connected, and in 

 another part by the muscle of Treitz. 



