322 



COMPARATIVE MORPHOLOGY OF VERTEBRATES 



veins and the hepatic portal system. The vertebral, or unpaired, veins, just 

 alluded to, unite with the subclavian and the jugular of the same side to form a 

 common trunk (really the Cuvierian duct) which is here called the precava (vena 

 cava anteiior) the postcava being the vena cava posterior. 



tnaxsup 

 tnoxM 

 intjuq 



Fig. 343. 



Fig. 



344. 



BIRDS. — Therejs a complete_diyision^jthe^ea£tj;n^ birds, 



and the right arch alone of the fourth primitive pair connects in the adult with 

 the dorsal aorta. There is the same formation of brachiocephalic arteries as was 



