1186 THE DIGESTIVE SYSTEM. 



infant, is placed some distance to the left of the ascending part of the duodenum. It is 

 produced by the inferior mesenteric vein raising up a fold of peritoneum, as it runs 

 medially along the side of the fossa, and then above it (see Fig. 934, where the vein, but 

 not the fossa, is shown). It is limited below by a special fold (the mesenterico-meso- 



colic fold). According to Moynihan, this is the 

 only fossa to the left of the duodenum capable 

 of developing into the sac of a hernia ; and 

 when this occurs, the inferior mesenteric vein 

 always lies in the anterior margin of the orifice 

 Duodenal of tlie sac (accompanied for some distance by 



papilla the ascending branch of the left colic artery). 



-Common open- 



'ancreaticduct Peritoneal Relations of the Duodenum. Whilst 

 ^puJaSnAtiidi- t ^ ie re l at> i ns of the peritoneum to the second and 

 nalis duodeni third portions of the duodenum are usually described 

 as in the foregoing account, it should perhaps be 

 pointed out, that it is not really the front, but the 

 right half of the circumference of the descending 

 portion which has a serous coat. Similarly, it is 

 the inferior and anterior half of the circumference 

 FIG. 935. THE PAPILLA DUODENI IN THE of the horizontal portion of the inferior part which 

 INTERIOR OP THE DUODENUM. is clothed by peritoneum, whilst considerably more 



than half of the circumference of its ascending 



portion is covered ; for the peritoneum forms a fold running in behind this portion, in addition 

 to covering its left side and half its anterior aspect. 



Interior of Duodenum. No plicae circulares are found in the duodenum for 

 an inch or two beyond the pylorus. They then begin ; at first as low, scattered, 

 and irregular folds ; further down, they gradually become larger, more regular 

 and more numerous ; and by the time the middle of the descending part is 

 reached they have attained a considerable development. In the inferior part of the 

 duodenum the folds are large, prominent, and closely set. 



On the inner aspect of the descending portion, about its middle namely, 3J 

 or 4 inches (8'7 to 10 cm.) beyond the pylorus is seen a prominent papilla, on 

 which the bile and pancreatic ducts open by a common orifice (Fig. 935). This is 

 known as the papilla duodeni (Santorini). 



The papilla duodeni is placed beneath, and protected by, a prominent, hood-like plica circu- 

 laris, which is situated immediately above it. From its lower margin a firm ridge of the 

 mucous membrane, the plica longitudinalis duodeni^ descends for a considerable distance, and 

 acts as a frenum, which fixes the papilla and directs its apex somewhat downwards (Fig. 935). 

 The papilla is prominent, and nipple or dome-shaped, and at its summit is placed the small 

 orifice, which will usually admit the point of a pencil ; the whole bears a close resemblance to 

 the nozzle of a perfume-spray. 



Nearly an inch higher up, and invariably on the ventral side of the papilla (sometimes as 

 much as a -^ to f inch distant), is seen a second and smaller papilla, the caruncula minor of 

 Santorini, at the point of which is placed the very small orifice of the accessory pancreatic 

 duct. This second papilla seems to be constantly present, although sometimes so small that it 

 may easily escape detection unless carefully sought for. When well developed, it may have a 

 hood -like plica circularis and a little frenulum, like those of the bile papilla. 



Structure of the Duodenum. The tunica serosa, which is incomplete, has already 

 been described in detail, in connexion with each part of the duodenum. 



The tunica muscularis is well developed, and is pierced by the bile and pancreatic 

 ducts, but otherwise calls for no special description. 



The tela submucosa diners from that of the rest of the small intestine, in that it 

 contains, especially in the superior half of the duodenum, the glandulse duodenales 

 [Brunneri]. These are small acino-tubular glands, closely resembling the pyloric glands 

 of the stomach; they lie in the submucous coat, and send their ducts through the 

 muscularis mucosse to open on the surface between the glandulse intestinales, or sometimes 

 into these glands themselves (Fig. 929). They can be exposed by the removal of the peritoneal 

 and muscular coats, and also some of the submucosa, when they appear as little round 

 or flattened masses of a reddish-gray colour, varying in size from -g^th to -^-th of an inch 

 in diameter ( - 5 to 2'0 mm.). They form an almost continuous layer as far as the opening 

 of the bile duct ; beyond this they diminish progressively, and completely disappear near 

 the duodeno-jejunal flexure. 



The tunica mucosa, which is thicker in the duodenum than in any other part of 

 the small intestine, is covered throughout with broad, short villi. 



