THE DUODENUM. 



1185 



The bile-duct, after passing down behind the- superior part of the duodenum, descends between 

 the head of the pancreas and the descending part, nearly as far as its middle ; there it is joined 

 by the pancreatic duct, and the two, piercing the wall of the duodenum obliquely, open by a 

 common orifice on its inner aspect, about 3 to 4 inches (87 to 10 cm.) beyond the pylorus. 



Pars Inferior. The inferior part (O.T. third portion) begins at the right side of 

 the third or fourth lumbar vertebra. It is described in two parts, fars horizontals, 

 transverse in direction, and pars ascendens', and it shows that arrangement in 

 Fig. 933. 



The pars horizontalis runs more or less transversely to the left across the inferior vena cava 

 (Fig. 933) for one or two inches, and the pars ascendens passes very obliquely, or even vertically, 

 upwards in front of the aorta and left psoas major muscle. Finally, having reached the inferior 

 surface of the pancreas, it bends forwards, and passes into the jejunum. 



Anteriorly, it is crossed (about the junction of its two divisions) by the superior mesenteric 

 vessels, and also by the root of the mesentery (Fig. 933). On each side of this it is covered by 

 coils of small intestine. Posteriorly, the pars horizontalis lies across the vena cava inferior ; the pars 

 ascendens lies on the aorta, the left renal vein and occasionally also the artery, and the left psoas 

 major muscle, all of which separate it from the vertebral column, Above, it is closely applied in 

 its whole extent to the head of the pancreas. The left side of the pars ascendens, which is free, 

 lies in contact with some coils of the small intestine. 



Peritoneal Relations. The inferior part of the duodenum is covered by peritoneum on its 

 anterior surface throughout, except where it is crossed by the superior mesenteric vessels and the 

 root of the mesentery, which contains these vessels (Fig. 933). In addition, its ascending part 

 is also clothed by this membrane on its left side. 



The attachment of the root of the mesentery begins, above, quite close to the duodeno-jejunal 

 flexure, on the front of the duodenum ; thence it runs down on the anterior aspect of the 

 ascending part, and finally leaves the duodenum about the union of the two divisions of its third 

 portion. 



Duodenal Fossae. In the neighbourhood of the pars ascendens are found three 

 well-known fossse of the peritoneum which are of some surgical interest ; they are the 

 superior and inferior duodenal and the paraduodenal fossse (Fig. 934). Other rarer forms 

 are occasionally present. 



When the ascending part of the duodenum is drawn over to the right, and the 

 angle between its left side and the posterior abdominal wall is examined, one or two 

 triangular folds of peritoneum 



Transverse colon. 



will generally be found cross- 

 ing over that angle from the 

 duodenum to the abdominal 

 wall. Each fold has one edge 

 attached to the duodenum, 

 another to the parietal peri- 

 toneum at the left of the 

 duodenum, whilst the third is 

 free, and bounds the opening 

 of a small pouch which lies 

 behind the fold, the recessus 

 duodeno -jejunalis. Of these 

 folds, the upper is termed the 

 plica duodeno-jejunalis, and it 

 is situated near the termina- 

 tion of the duodenum, with its 

 apex directed up and its free 

 margin down. It sometimes FIG. 934. THE DUODENAL Foss^ AND FOLDS. 



contains between its two layers The transverse colon and mesocolon have been thrown up, and the 

 the termination of the inferior mesentery has been turned to the right and cut. The paraduodenal 



mesenteric vein. Behind it fossa < of Landzert ) is situated to the medial side of the inferior 

 lies a prolongation from the 

 recessus duodeno-jejunalis 

 termed the superior duodenal fossa. Its opening looks downwards, and will usually 

 admit the tip of a finger (Fig. 934). The second, known as the plica duodeno-mesocolica, 

 is placed lower down, at the side of the same part of the duodenum. Its free border is 

 directed upwards, as is the mouth of the inferior duodenal fossa, which lies behind it. 

 This latter is larger and more constant than the superior duodenal fossa, and is present 

 in 75 per cent, of bodies, whilst the superior is present in 50 per cent. (Jonnesco). 



Paraduodenal Fossa (fossa of Landzert). This fossa, which is seen best in the 



76 



Transverse meso- 

 colon 



Duodenum 



3rior 

 duodenal' fossa 



Inferior 

 duodenal fossa 



The mesentery (cut) 



Inferior mesenteric vein 

 Left colic artery 



mesenteric vein, between it and the terminal part of the duodenum. 

 It is not shown in the illustration. 



