THE DEVELOPMENT OF THE VASCULAR SYSTEM 



263 



extends along the radial side of the extremity and becomes connected with 

 the digital veins (Fig. 242). When the digital veins are taken up by the 

 cephalic, the distal portion^ of the primitive ulnar undergoes regression. 

 These changes have taken place in rabbit embryos of fifteen days, and for a 

 short period the cephalic vein is the chief vessel of the extremity. The 

 primitive ulnar vein, however, develops more rapidly than the cephalic and, 



Heart- 



Inf. vena cava - 



Ductus venosus 



Left lobe of liver- 



Umbilical vein 



Umbilical ring 



Hepatic veins 



Right lobe of liver 



Gall bladder 



Portal vein 

 (omphalomesenteric; 



Intestine 



Inf. vena cava 



FIG. 240. Veins of the liver (seen from below) of a human foetus at term Kollmann's Atlas. 



with its branches, soon becomes the chief vessel; the portion in the forearm 

 gives rise to either the ulnar or basilic vein; the portion in the arm becomes 

 the brachial vein which then passes over into the axillary, and the latter 

 in turn passes over into the subclavian. The cephalic vein of the embryo 

 persists as the cephalic of the adult, and, during the period when it forms the 

 chief vessel of the extremity, a branch arises from it which becomes the radial 

 vein. Primarily the cephalic vein opens into the external jugular, but later 



