Charles F. W. McClure 13 
sists in reptiles, birds and the rabbit of two principal subdivisions which 
are genetically independent of each other; one of which is formed be- 
tween the sinus venosus and the hepatico-subcardinal junction and the 
other between the latter and the cross anastomosis between the subcardi- 
nals. The latter subdivision is formed in all three cases from a portion 
of the right subeardinal vein; while the former has a somewhat different 
OMPHALOMESENTER 
ARTERY 
POST, REVEHENT 
VEINS 
Fig. 8. 
Fic. 8. Reconstruction of the venous system of a chick embryo of five days 
incubation in which the subcardinals form a venous ring about the origin of 
the omphalomesenteric artery as in Lacerta. After Miller. Ventral view. 
origin in reptiles, birds and the rabbit which need not be mentioned here. 
There is one feature at this period of development, however, in which 
the venous system of the rabbit differs from that of reptiles and birds. 
In the rabbit (Text Fig. 6) the unpaired postcava is connected at its 
caudal end with each posteardinal vein by means of large anastomoses so 
that a continuous and uninterrupted channel is established between the 
