284 



THE SIXTH DAT. 



[chap. 



the heart by two main venous trunks, the superior (Fig. 

 58, J) and inferior (Fig. 58, 0) cardinal veins, joining 

 on each side to form the short transverse ductus Cuvieri, 

 both which in turn united with the sinus venosus close 

 to the heart. As the head and neck continue to enlarge 

 and the wings become developed, the single superior 

 cardinal or jugular vein, as it is usually called (Figs. 89, 

 90, J), of each side, is joined by two new veins : the 



Fio. 89. 



Diagram of the Venous Circulation at the Commencement 

 OF THE Fifth Day. 



n. heart, d.a. ductus Cuvieri. Into the ductus Cuvieri of each 

 side fall J. the jugular vein, W. the vein from the wing and 

 C. the inferior cardinal vein. S. V. sinus venosus. Of. vitel- 

 line vein. U. allantoic vein, which at this stage gives off 

 branches to the body-walls. V.C.I, inferior vena cava. 

 I. liver. 



vertebral vein {8u. J. V.), bringing back blood from the 

 head and neck, and the vein from the wing ( W). 



The inferior cardinal veins have their roots in the 

 Wolffian bodies; they become developed, pari passu, 



