180 Venous System of Didelphys Marsupialis (1) 
tween the sinus venosus and the hepatico-subeardinal junction (Text 
Fig. 11) the posteava is without doubt formed, as in the rabbit, inde- 
pendently of the right subeardinal vein. The remaining portion of the 
unpaired postcava, that section of the vein which hes caudad of the 
hepatico-subcardinal junction, is formed from the right subeardinal vein 
with the exception of a portion near the hepatico-subcardinal junction 
which is partially embedded in the parenchyma of the liver and which is 
formed from the hepatic sinusoids in conjunction with the right sub- 
cardinal vein. ‘The term hepatico-subcardinal junction refers to the 
most cranial of the anastomoses that may exist between the right sub- 
cardinal and the hepatic circulation (Text Fig. 11) since in some cases 
the section of the posteava which is formed from the hepatic sinusoids 
and which hes partially embedded in the liver does not fuse along its en- 
tire extent, but only at intervals, with the right subeardinal vein. Fig. 
34, Plate II, represents the section preceding and Fig. 35, Plate II, a 
section taken through the hepatico-subcardinal junction in which it is 
seen that ventrally the postcava is formed by hepatic sinusoids and dor- 
sally by the right subeardinal vein. Slightly caudad of the hepatico-sub- 
cardinal junction the posteava lies upon the dorsal surface of the liver 
(Fig. 36, Plate II), where, as well as caudad of the liver itself (Figs. 
37 and 38, Plate III), it occupies the same relative position with respect 
to the mesonephros and suprarenal body and, with the exception of those 
from the liver, receives the same class of tributaries as the anterior reve- 
hent vein of the left side (left subeardinal). These tributaries are veins 
from the suprarenal body, the mesonephros, the genital anlage and from 
the tissue ventral to the aorta. Finally, the pars subcardinalis of the 
postcava does not, as in Dasyurus, anastomose at intervals along its course 
with the right postcardinal vein; the absence of such connections being 
probably correlated with the degeneration of the postcardinal vein. 
The Anterior Revehent Veins—The right anterior revehent vein (Text 
Fig. 11 and Fig. 34, Plate II) is derived from that portion of the right 
subeardinal which lies craniad of the hepatico-subcardinal junction. The 
left anterior vein (Figs. 10 and 11 and Figs. 34, 35 and 36, Plate IT, and 
Fig. 37, Plate III) consists of that portion of the left subcardinal which 
lies craniad of the anastomosis (Fig. 38, Plate III) between the two 
subeardinals. In the 8 mm. embryos of Didelphys this anastomosis be- 
tween the two subeardinals (cross anastomosis) is, as a rule, more exten- 
sive and complete than in the 6 mm. embryo of Dasyurus so that the left 
anterior revehent vein usually has the appearance of opening into the 
posteava rather than being directly continuous caudad, as in the Dasyu- 
rus embryo (Text Fig. 9), with the left posterior revehent vein. In one 
