CH. LVIII.] 



THE FCETAL CIRCULATION. 



837 



sources, through the umbilical and portal vein respectively. At 

 birth the circulation through the umbilical vein of course com- 

 pletely ceases and the vessel begins at once to dwindle, so that 

 now the only venous supply of the liver is through the portal vein. 

 Another system of veins which appears early, consists of 

 two short transverse veins (ducts of Cuvier) which open into the 

 right auricle on cither side ; each is formed by the union of an 



r, renal veins ; i I, iliac veins ; h ij, hypogostric veins. (Oegenbaur.) 



anterior cardinal, afterwards forming a jugular, vein, collect- 

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

 which returns the blood from the Wolftian bodies, the vertebral 

 column, and the parietes of the trunk. This arrangement persists 

 throughout life in fishes, but in mammals the following trans- 

 formations occur. 



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

 inferior), 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 this 

 time have lost their original opening into the ductus venosus. 

 The heart gradually descends into the thorax, causing the ducts 

 of Cuvier to become oblique instead of transverse. As the fore- 

 limbs develop, the subclavian veins are formed. 



