304 THE ABDOMEN AND PELVIS 



first flexure of the duodenum sinks downwards,, sometimes, to 

 the second lumbar vertebra. The proximal inch or less of the 

 first part is freely movable as it is invested by the same two 

 layers of peritoneum as enclose the stomach. Its upper border 

 is related to the lesser omentum and the right gastric (pyloric) 

 artery, and its lower border to the greater omentum and the right 

 gastro-epiploic artery. Behind it lies a small recess of the 

 omental bursa. The distal inch or more of this part receives 

 from the peritoneum only an anterior covering so that its range 

 of movement depends entirely on the elasticity or looseness of 

 its peritoneal coat. Its posterior, or postero-medial, surface is 

 in immediate relation to the bile-duct, portal vein, and gastro- 

 duodenal artery, while the inferior vena cava is separated from 

 it by these structures and by some areolar tissue (Fig. 87). 



The whole of the antero-lateral surface of the first part of 

 the duodenum lies in the supra-colic subdivision of the peritoneal 

 cavity. This aspect is the commonest site of duodenal ulceration, 

 and perforation will primarily infect the supra-colic compartment. 

 On the other hand, perforation of an ulcer on the postero-medial 

 surface will, if it is situated close to the pylorus, at once involve 

 the omental bursa; but if it is placed more distal ly, the infection 

 will be retroperitoneal and may pass up along the inferior vena 

 cava to the extra-peritoneal subphrenic area (p. 310). 



As the closure of such perforations results in marked narrowing 

 of the lumen of the gut, gastro-enterostomy is usually performed 

 lest complete obstruction should follow. 



Mayo has suggested that the frequency with which duodenal 

 ulcer occurs on the antero-lateral wall is determined by the fact 

 that the over-acid chyme, as it is squirted through the pylorus, 

 incessantly impinges on this wall and produces repeated minute 

 traumata. It has also been urged that the area in question is 

 supplied by a small branch from the hepatic or gastro-duodenal, 

 and that its terminal twigs are end-arteries, i.e. do not anastomose 

 with other vessels in the neighbourhood. Thrombosis in this 

 artery, therefore, would in all probability give rise to necrosis 

 of the area supplied by it. In childhood, however, the anasto- 

 mosis is complete. 



The Descending or Second Portion passes downwards 

 from the neck of the gall-bladder along the medial border of 

 the right kidney to the level of the third lumbar vertebra, lying 

 in front of the hilum of the kidney and the commencement of 

 the ureter. It is crossed anteriorly, in its lower part, by the 



