DEVELOPMENT. 



liver, and, having passed through its capillaries, returns to the umbili- 

 cal vein through the venae hepaticse revehentes at a point nearer the 

 heart (see fig. 498) . The portion of vein between the afferent and effe- 

 rent veins of the liver becomes the ductus venosus. The venae hepaticae 



Fig. 498. Diagrams illustrating the development of veins about the liver. 5, d c, ducts of 

 Cuvier, right and left ; c a, right and left cardinal veins ; o. left omphalo-mesenteric vein ; o', 

 right omphalo-mesenteric vein, almost shrivelled up ; u u', umbilical veins, of which it', the right 

 one, has almost disappeared. Between the venae cardinales is seen the outline of the rudiment- 

 ary liver with its venae hepaticae advehentes, and revehentes. Z>, ductus venosus; I', hepatic 

 veins; c i, vena cava inferior; P, portal vein; P'P'. venae advehentes; m, mesenteric veins. 

 (Kolliker. ) 



advehentes become the right and left branches of the portal vein, the 

 venae hepaticae revehentes become the hepatic veins, which open just at 

 the junction of the ductus venosus with another large vein (vena cava 

 inferior), which is now being developed. The mesenteric portion of 

 the omphalo-mesenteric vein returning blood from the developing intes- 

 tines remains as the mesenteric vein, which, by its union with the splenic 

 vein, forms the portal. 



Thus the foetal liver is supplied with venous blood from two sources, 

 through the umbilical and portal vein respectively. At birth the circu- 

 lation through the umbilical vein of course completely ceases and the 

 vessel begins at once to dwindle, so that now the only venous supply of 

 the liver is through the portal vein. The earliest appearance of the 

 parietal system of veins is the formation of two short transverse veins 

 (ducts of Cuvier) opening into the auricle on either side, which result 

 from the union of an anterior cardinal, afterward forming a jugular, vein, 

 collecting blood from the head and neck, and a posterior cardinal vein 

 which returns the blood from the Wolfl&an bodies, the vertebral column, 

 and the parieties of the trunk. This arrangement persists throughout 

 life in fishes, but in mammals the following transformations occur. 



As the kidneys are developing a new vein appears (vena cava infe- 

 rior), formed by the junction of their efferent veins. It receives branches 

 from the legs (iliac) and increases rapidly in size as they grow; further 

 up it receives the hepatic veins, which by now have lost their original 

 opening into the ductus venosus. The heart gradually descends into 



