1648 



HUMAN ANATOMY. 



^\\& inferior duodenal fossa (Fig. 1400) is the most common form, occurring, 

 according to Jonnesco, in 75 per cent. , and to Treves in 40 per cent. It is non- 

 vascular, formed by a fold of peritoneum passing from the left of the fourth part of 

 the duodenum to the posterior wall, with a free concave edge looking upward. The 

 pocket extends down behind this fold for a variable distance. It may reach the 

 fourth lumbar vertebra. 



The superior diwdenal fossa occurs in 50 per cent. This corresponds to the 

 preceding, only it runs upward behind a fold, with a concave free edge looking 

 downward, passing from the duodeno-jejunal flexure to the posterior wall on the 

 left. The pocket is less deep than the preceding. It is usually vascular, the in- 

 ferior mesenteric vein running in the fold, sometimes near its edge. These two 

 fossae frequently coexist, and the left ends of the folds may be continuous, so as to 

 form a large C-shaped fold, open to the right, with a pocket under both the upper 

 and the lower limbs. In this case the vein may be in the vertical part of the fold. 

 An arterial arch, formed either by the ascending branch of the left colic artery or 

 by the left branch of the middle colic, is often very close to the vein. Such a 

 pouch may extend deeply under the fourth part of the duodenum. 



The mesocolic fossa,^ found in 20 per cent., and always alone, is a little pocket 

 on the top of the duodeno-jejunal flexure under a fold from the posterior layer of the 

 transverse mesocolon. When this membrane is reflected so as to show it, the fossa 



appears to run upward. The in- 



FiG. 1401. 



ferior mesenteric vein may be in 

 the fold. 



The paraduodenal fossa is in 

 the peritoneum of the posterior 

 abdominal wall, less intimately 

 connected with the gut than the 

 others. It is a pocket formed by 

 the superior branch of the left colic 

 artery raising a fold of the perito- 

 neum. The mouth of the pouch 

 is to the right. It is not uncom- 

 mon in the infant, rare in the adult. 

 The rctroduodenal fossa is an 

 uncommon pouch under the third 

 and fourth parts of the duodenum, 

 extending upward with the mouth 

 below. 



Interiorof the Duodenum. 

 — The mucous coat is smooth in 

 the first part and overlies tht 

 glands of Brunner (page 1639). 

 which lie chiefly within the submucosa and form a continuous layer for some 4 or 

 5 cm. ; beyond they are scattered for some distance farther. The villi are small at 

 the beginning, but soon attain their complete size. The valvulae conniventes are at 

 first absent for about 4.5 cm., appearing at the end of the first part, and are almost 

 at once large, near together, and non-effaceable. A very large one is formed by the 

 folding in of the wall at the junction of the first and second parts ; beyond this the 

 valves at once reach their greatest development. In the second part the bilc-papilla 

 is seen in the back part of the left or inner wall, from 8.5-10 cm. (about 3,i<-4 in.) 

 beyond the pylorus, or rather below the middle, through which the common bile-duct 

 and the duct of the pancreas pass to open by a common orifice. The papilla is almost 

 always overhung by a valvular fold (Fig. 1401 ), and when non-distended is only some 

 5 mm. long. The accessory duct of the pancreas often opens 2 or 3 cm. above 

 the main one through a much smaller and inconstant papilla. The submucous coat 

 holds the mucous membrane pretty firmly in place, so that the folds are permanent. 



' Jonnesco calls this also the fosseile duodeno-jejunale ; but, although following him other- 

 wise, we have retained duodenal as the generic name. 



Surface view of mucous membrane of duodenum ; entrance of 

 bile and pancreatic ducts shown by probe, which lies in bile-duct. 

 Papilla is surrounded by hood-like fold. Natural size. 



