THE PORTAL CIRCULATION 275 



At the upper end of the abdominal alimentary canal, the 

 left gastric (coronary) vein on the lesser curvature communi- 

 cates with the cesophageal veins, which open indirectly into 

 the superior vena cava. In portal obstruction this anastomosis 

 becomes greatly dilated and may form varices in the lax 

 submucous tissue of the lower part of the oesophagus. Rupture 

 of these veins causes h&matemtsis which may be the first 

 sign of portal cirrhosis. 



At the lower end of the abdominal alimentary canal, the 

 superior hsemorrhoidal veins, which return their blood via 

 the inferior mesenteric and splenic veins to the portal system, 

 communicate freely with the middle and inferior haemorrhoidal 

 veins, which open indirectly into the inferior vena cava. 

 Dilatation of this anastomosis and the production of internal 

 hemorrhoids is favoured by (i) the action of gravity, (2) the 

 absence of valves, and (3) the fact that the radicles of the 

 superior haemorrhoidal veins ascend in the submucous tissue 

 of the rectum for some distance before piercing the muscular 

 wall (p. 284). 



The mesenterie and splenic veins communicate with the 

 veins of the posterior abdominal wall, which ultimately 

 open into the inferior vena cava. It is said by some 

 authorities that, in the rare event of complete compensation, 

 it is this anastomosis which carries off by far the greatest part 

 of the obstructed blood. 



An extremely interesting communication is established 

 through the medium of the para-umbilical veins. These small 

 vessels, which unfortunately are not always present, are con- 

 nected above to the left branch of the portal vein and they 

 descend on the obliterated umbilical vein (ligamentum teres, 

 p. 260) to the umbilicus, where they establish communications 

 with the superficial veins of the anterior abdominal wall 

 (p. 316). When this anastomosis becomes dilated the super- 

 ficial abdominal veins are rendered visible through the skin. 

 They are large and tortuous, and they radiate from the 

 umbilicus, so that the general appearance has been termed 



