PORTAL SYSTEM. 



131 



the capillaries, but the explanation is found by taking into 

 account the exceedingly short distance of capillary circula- 

 tion traversed by each portion of blood, probably in no case 

 exceeding the tenth of an inch. 



Fig. 71. VENOUS SYSTEM, diagrammatic view. , Trachea dividing 

 into the two bronchi; 6, aorta dividing into the two common 

 iliac arteries, which again divide into the external and internal 

 iliacs ; c, c, kidneys, with the renal veins emerging from them ; 

 d, liver ; e, spleen ; /, portion of intestine, with mesenteric vein, 

 proceeding from it to join the splenic and form the portal vein, 

 which branches in the liver ; g, inferior vena cava receiving the 

 hepatic veins emerging from the liver ; h, obliterated umbilical 

 vein; i, obliterated ductus venosus; k, superior vena cava formed 

 by union of the two innominate or brachio-cephalic veins ; Z, the 

 right vena azygos joined by the left. 



96. Portal System. Before leaving the subject of the 

 circulation, it remains to be pointed out that there are 

 exceptions to the rule that the arteries continually divide 



