146 Vertebrate Embryology 



carry the blood back to the vascular area, 

 whence it was brought, it will be remembered, 

 by the vitelline veins. 



The details in the development of the blood 

 and the blood vessels have been differently 

 described by different workers. 



YOR! 



FIG. 49. VENTRAL VIEW OF THE ANTERIOR REGION OF THE EM- 

 BRYO SHOWN IN FIG. 47. (After Duval.) 



Ao, bulbus arteriosus. C, heart, curved towards the right side of the embryo. 

 /, lateral limit of the cavity of the pharynx. V 1 , fore-brain. Vo, optic vesicle. 

 ^ vitelline vein. 



According to one view, the entire vascular 

 system is derived from mesoblast ; according 

 to another view, the endotheljal lining of the 



