THE DUODENUM. 



839 



are no distinct lines of demarcation between these three parts, but there 

 are certain peculiarities of connection and certain differences of internal 

 structure to be observed in comparing the upper and lower ends of the 

 entire tube, which will be pointed out after it has been described as a 

 whole. 



DUODENUM. This is the shortest and widest part of the small intes- 

 tine. In length it measures 10 or 12 inches, or nearly tha breadth of 

 twelve fingers ; hence its name. 



It is the widest part of the small intestine, varying in diameter between 

 an inch and a half and two inches. In its course it describes a single 

 large curve somewhat resembling a horse-shoe, the convexity of which is 

 turned towards the right, whilst the concavity embraces the head of the 

 pancreas. 



It has no mesentery, and is covered only partially by the peritoneum. 

 Its muscular coat is comparatively thick, and its mucous membrane towards 



Fig. 586. 



Fig. 586. VIEW OF THE DUODENUM FROM 

 BEFORE (slightly altered from Luschka). \ 



12, the twelfth dorsal vertebra and rib ; 1, 

 3, 4, 5, transverse processes of the first, third, 

 fourth, and fifth left lumbar vertebrae ; 2, 

 that of the second on the right side ; a, a, 

 the abdominal aorta above the coeliac axis and 

 near the bifurcation ; m, superior mesenteric 

 artery ; v, v, the vena cava above the renal 

 veins and near the bifurcation ; p, placed on 

 the first part of the duodenum, points to the 

 pyloric valve seen from the side next the 

 stomach, of which a small part is left con- 

 nected with the intestine ; d, on the descend- 

 ing or second part of the duodenum, indicates 

 the termination of the common bile-duct and 

 the pancreatic duct ; d\ the third or oblique 

 part of the duodenum ; j, the commencement 

 of the jejunum. 



the pylorus is the seat of the com- 

 pound glands of Brunner, to be sub- 

 sequently described. The common bile-duct and the pancreatic duct open 

 into this part of the intestinal canal. 



Three portions of the duodenum, differing from each other in their course 

 and connections, are separately described by anatomists ; viz., the superior, 

 descending, and transverse portions. 



The first, or superior portion, which is between two and three inches long, 

 commences at the pylorus, and passing upwards, backwards, and to the right 

 side, reaches as far as beneath the neck of the gall-bladder, where the 

 intestine bends suddenly downwards. The first portion of the duodenum is 

 for the most part free, and invested both in front and behind by the peri- 

 toneum. Above, and in front of it, are the liver and gall-bladder, and it is 

 commonly found stained by the exudation of bile from the latter a few 

 hours after death. Behind it is the hepatic duct, with the blood-vessels 

 passing up to the liver. 



The second, or descending portion, commencing at the bend below the 

 neck of the gall-bladder passes vertically downwards in front of the right 

 kidney, as low as the second or third lumbar vertebra, where the bowel 

 turns across to the left to form the third portion. This part of the 



