798 



COMPARATIVE ANATOMY 



times a branchial vein which may empty into the sinus venosus. In the 

 amphibia a cutaneous magnus vein comes from the skin of the trunk 

 which may enter the subclavian. In all tetrapoda, the subclavian, after 

 it leaves the limb, receives a superficial cephalic and an axillary vein. 

 The latter, however, changes its name in the appendage to the brachial 

 vein. The common iliac vein is formed in the limb by a union of the 

 femoral and sciatic (ischiadic) veins, as well as the hypogastric (inter- 

 nal iliac) vein. 



In all classes above fishes, such as dipnoi, amphibia, and amniotes, 

 a new vein, the postcava (vena cava inferior) arises in part from scat- 

 tered spaces and in part as a diverticulum of the sinus venosus and the 

 hepatic veins. It grows backward, dorsal to the liver, until it meets and 

 fuses with the right subcardinal vein, a portion of which now forms a 

 new trunk to carry blood from the posterior part of the body to the 

 heart. 



The following changes are introduced in the embryonic renal portal 

 circulation whenever a postcaval vein develops. The subcardinals no 

 longer connect with the caudal vein but are connected with each other 

 by transverse vessels (interrenal veins). Portions of the postcardinals 

 grow backward to connect with the caudal vein. These posterior parts 

 of the postcardinals then become the advehent veins (Fig. 452) of a sec- 



B. 



Diagram of Renal Portal System in A, Alligator, and B, Bird. (After 

 Gegenbaur. ) 



