Fig. 107. The change from the 

 simple, direct cardinal circulation to 

 the indirect, renal portal circulation. 

 The circulation of the blood is 

 traced by arrows from the posterior 

 body region, lower left, through 

 the posterior cardinal vein into the 

 common cardinal and thence to the 

 heart. A new vein, the subcardinal, 

 joins the posterior cardinal at B. 

 This new vein then connects with 

 the ductus venosus in the liver by 

 means of vessel A. When the cir- 

 culation is blocked at C and at B, 

 blood flows from the posterior car- 

 dinal vein through the mesoneph- 

 ros, D, and thence by means of A 

 through the liver and into the heart. 



PORTAL VEIN 



'MESONEPHROS 

 POSTERIOR CARDINAL 



Fig. 108. The change from the 

 indirect renal portal circulation to 

 the adult type. The mesonephros de- 

 generates and the renal portal cir- 

 culation ceases. New connections at 

 G carry the blood directly into the 

 branches of the inferior vena cava. 



