640 THE AMERICAN NATURALIST. 
with the posterior vena cava on the left side, just opposite the 
right ovarian vein. 
a.b., abnormal connecting vein; 
a.m., anterior mesenteric vein ; 
^ bertus vein ; k., , kidne ey i ; 
vill 
"1 ovarian vein ; pP d 
P 
vein; 
teric vein, 7.v., posterior vena 
cava ; rec., rectum ; z.2v., right 
ovari ein 
This connecting branch was not modified 
from some of the branches of the vena 
cava normally belonging to this region, 
since these were all present. It may 
possibly have been one of the original 
branches composing the posterior mesen- 
teric which had in some way become 
attached to the vena cava. 
Some correlation might be made with 
the birds, since they have the portal vein 
and the posterior vena cava normally con- 
nected by the posterior mesenteric and 
the hypogastric veins. Such is, however, 
not justifiable, for this is, so far as I know, 
the only record of such an existence in 
mammals. It is best, therefore, to con- 
sider it strictly as an abnormality and in 
no sense a reversion to some possible past 
condition. 
In conclusion I may add that, though 
no attempt will be made to account for 
the causes leading to these abnormalities 
in cats and rabbits, I do not feel that 
domestication should be mentioned as a possible cause, since 
these variations occur as frequently in the wild rabbit as in 
the domesticated cat. 
