422 EMBEYOLOGY OF THE LOWER VEETEBEATES ch. 



the hind end of the heart. The two vitelline veins become connected 

 by a transverse anastomosis dorsal to the gut and just behind the 

 dorsal pancreatic rudiment (Fig. 195, B). The parts of the veins in 

 front of this anastomosis break up into a network in the substance of 

 the liver, and the two networks become continuous with one another 

 (Fig. 195, C). The two vitelline veins now form another anastomosis 



rail 



loll 



p.vc 



ruu- 



l.v.u 



rail 



loll 



p.ve. 



Air. 



loll. 



rall- 



* ah. 



AC 



ent. 



Lall 



Pig. 195. — Diagrams to illustrate the development of the ventral part of the venous 

 system in Lacerta agilis as seen from the ventral side. (After Hochstetter, 1892.) 



ab, abdominal vein; d.C, duct of Cuvier ; d.v, ductus venosus ; ent, alimentary canal; l.all, left 

 allantoic vein ; li, liver ; l.v.v, left vitelline vein ; p, portal vein ; p.v.c, posterior vena cava ; r.all, right 

 allantoic vein ; r.v.v, right vitelline vein. 



with one another farther back and ventral to the alimentary canal 

 (Fig. 195, C). The right vitelline vein becomes reduced and finally 

 obliterated in the region in front of this ventral anastomosis so that 

 the whole blood-stream passes forwards to the level of the dorsal 

 anastomosis by the persistent left vein (Fig. 195, D, l.v.v). In the 

 region anterior to the dorsal anastomosis the left vein now diminishes 

 in size and finally disappears, first in the region behind the hepatic 



