1018 THE DIGESTIVE SYSTEM. ‘ 
The third or inferior portion (pars inferior) begins at the right side of the third 
or fourth lumbar vertebra. From this it first runs more or less transversely to the 
left across the vena cava (Fig. 687) for one or two inches, and then passes very 
obliquely, or even vertically, upwards in front of the aorta and left psoas muscle. 
Finally, having reached the lower surface of the pancreas, it bends forwards, and 
passes into the jejunum. Owing to the different directions which they take, we 
can recognise two divisions, a transverse and an ascending terminal, in this 
portion of the duodenum (Fig. 687). 
In front, it is crossed (about the junction of its two divisions) by the superior 
mesenteric vessels, and also by the root of the mesentery (Fig. 688). On each 
side of this it is covered by coils of small intestine. Behind, its horizontal portion 
lies on the vena cava; its ascending portion on the aorta, the left renal vessels, 
and the left psoas 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 ascending terminal part, which is free, lies in contact with some coils 
of the small intestine. 
Peritoneal relations—The third portion of the duodenum is covered by peri- 
toneum on its anterior surface throughout, except where it is crossed by the 
superior mesenteric vessels and the root of the mesentery which contains them 
(Fig. 688). In addition, its ascending terminal portion is also clothed by this mem- 
brane on its left side; and here are usually found one or two small peritoneal 
pouches known as the duodenal fosse. 
The attachment of the root of the mesentery begins above quite close to the duodeno-jejunal 
flexure, on the front of the duodenum; from this it runs down on the anterior aspect of the 
ascending terminal part, and finally leaves the duodenum about the union of the two divisions 
of its third portion. 
Duodenal Fossz.—In the neighbourhood of the ascending part of the third 
portion of the duodenum are found three well-known fossie of the peritoneum which are 
of some surgical interest; these are the superior and inferior duodenal and the paraduo- 
denal fossee (Fig. 689). Other rarer forms are occasionally present. 
When the ascending terminal part of the duodenum is drawn over to the right, 
and the angle between its left side and the posterior abdominal wall examined, one or 
ee Ry ee EO triangular folds of peri- 
Transverse colon, ot colon toneum will generally be found 
< ee vA crossing over this angle from 
the duodenum to the abdo- 
minal wall. Each fold has 
one edge attached to the 
duodenum, another to the 
parietal peritoneum at the left 
of the duodenum, whilst the 
third is free, and bounds the 
opening of a small pouch which 
lies behind the fold. One of 
these,.the saperior duodenal 
fold, is situated near the ter- 
mination of the duodenum, 
Inferior mesenteric vein with aS ae directed UP 
Inferior mesenteric artery and its free margin down. It 
sometimes contains between its 
two layers the termination of 
The transverse colon and mesocolon have been thrown up, and the the inferior mesenteric vein. 
mesentery has been turned to the right and cut. The paraduodenal Behind it lies the superior 
fossa (of Landzert) is situated to the inner side of the inferior 
mesenteric vein, between it and the terminal part of the duodenum. duodenal fossa, the Seer ties of 
It is not shown in the illustration. which looks downwards, and 
will usually admit the tip of 
a finger (Fig. 689). The second, known as the inferior duodenal fold, 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). 
Duodenum — 
Superior —< 
duodenal fossa 
Inferior —— 
duodenal fossa 
Fic. 689.—-THE DUODENAL Foss AND FOLDS. 
