CHAPTER XVI. 



DEVELOPMENT OF THE CIECULATOEY SYSTEM. 



Veins. — (1) The Superior Vena Cava arises from the following 

 foetal vessels (Figs. 181 and 182): 



(a) The part above the entrance of the vena azygos is the 

 terminal part of the right primitive jugular or anterior cardinal 

 vein ; 



(b) The part below the entrance of the vena azygos major 

 arises from the right duct of Cuvier. The condition of these 

 venous trunks, the anterior and posterior cardinal veins and Ducts 

 of Cuvier, in a human embryo of the 3rd week is shown in Fig. 

 182. The condition shown is retained permanently in lower 

 vertebrates (Fishes, etc.). 



rt. subclau. 



prim. jug. 



from prim. jug. 



pericardium cardin. ueinf 

 from rt. d. of Cuvier 



rt. aur. 



perwar. 

 \ ( aur. 



'sin. uen. 



I 



\'- left duct 



pleura of Cuvier 



/( rt. duet 

 \of Cuvier 



Fig. 181. 



Fig. 182. 



Fig. 181.— The Superior Vena Cava of the Adult. 



Fig. 182.— The Embryonic Venous Trunks out of which the Superior Vena Cava 

 is formed. 



The anterior Cardinal or primitive Jugular Vein, which drains 

 the anterior half of the body on each side with the posterior 



