480 Description of a 4-mm. Human Embryo 
Pa. pancreas. 
P. card.=posterior cardinal vein. 
Pl=plexus. 
S. ven.=sinus venosus. 
Sip. ¢spinal cord: 
Um. ar=umbilical artery. (Rt. and It.) 
Um. v.=umbilical vein. (Rt. and It.) 
V.=vein. 
V. pl=ventral plexus. 
Vent.=ventricle. 
Vit. v.vitelline vein. (Rt. and It.) 
W. d.— Wolffian duct. 
W. d’.—entrance of Wolffian duct into cloaca. 
W. t.= Wolffian tubule. 
