Charles F. W. McClure. 181 
of the 8 mm. embryos, however, the fusion between the two subcardinals 
was not as complete as in some of the others so that the left anterior re- 
vehent vein could be traced directly craniad from the left posterior re- 
vehent vein (See Text Fig. 12). Both of the anterior revehent veins 
occupy the same relative position in the embryo with respect to the supra- 
renal bodies and the mesonephroi and, with the exception of the direct 
anastomoses with the postcardinals which are wanting, receive the same 
class of subeardinal tributaries as the corresponding veins in the 6 mm. 
embryo of Dasyurus. 
The Posterior Revehent Veins.—The right and left posterior revehent 
veins (subeardinals) which he caudad of the cross anastomosis can, in 
RIGHT 
ANT. REVEHENT 
VEIN 
SUBCARDINAL 
HEPATICO-SUBCARDINAY 
LEFT 
JUNCTION E 
m—— ANT. REVEHENT. 
VEIN 
POSTCARDINSL SUBCARDINAL 
POSTCAVA 
PARS SUBCARDINALIS: POSTCARDINAL 
CROSS ANASTOMOSIS 
POSTCARDINA 
POST. REVEHENT 
VEINS 
SUBCARDINAL 
Ge: 
Fic. 12. Reconstruction of the venous system of an 8 mm. embryo of Didel- 
phys in the region of the original cross anastomosis between the subcardinals. 
Ventral view. 
most of the 8 mm. embryos, be traced as continuous vessels between the 
cross anastomosis, into which they open cranially, and the hinder end of 
the body where they sometimes aid in the formation of the venous rings 
which encircle the umbilical arteries. Each posterior revehent vein lies 
ventral to the mesonephrie arteries on the medial side of the mesonephros 
and receives tributaries from the latter as well as from the genital anlage 
and tissue ventral to the aorta (Fig. 39, Plate III). Each vein also 
anastomoses at intervals along its course with the postcardinal vein of the 
same side as well as with a complicated system of vessels which, for the 
most part, lies dorsal or dorsolateral to it and which I shall describe under 
the name of the cardinal collateral system of veins (Vy. cardinales col- 
laterales). 
