The Arteries 



321 



Fio. I'l. Ri I otistruction of human einl>i\<) df about 17 days 

 (His): ov, optic vesicle, ot, otic vesicle; nc, nc', notochord ; 

 hdg, head gut ; vs, vitelline sac ; 1, liver; v, ta, primitive ven- 

 tricle and truncus arteriosus ; va and da, ventral and dorsal 

 aorta; ; aa, aortic arches ; jv, primitive juglar vein ; cv, cardinal 

 vein ; dC, duct of Cuvier ; uv,ua, umbilical vein and artery ; al, 

 allantois ; uc, umbilical cord. (Heisler). 



