1909. ] POSI'CAVAL VEIN IN MAMMALS. 523 
Thus the Marsupials possess a general character of the post- 
caval and its branches which is shared by no other group of 
mammals. Furthermore, it is very noteworthy that within this 
particular group the variations in important matters is but slight. 
Thus the only features which differ at all from genus to genus or 
from species to species are the symmetry or asymmetry of the 
renals, the exact origin of the suprarenal vein of the left side, 
whether from the left renal or from an adjacent part of the post- 
caval, and the freedom or connection by anastomoses of the 
anterior pair of veins which leave the renals on each side together, 
and finally their connection or perhaps non-connection by anas- 
tomoses with the posterior spermatic veins where they cross 
them dorsally on their way to the testes or ovaries. It will have 
been observed that it is quite impossible to distinguish the 
Carnivorous from the Diprotodont Marsupials by their veins; 
the whele group of the Marsupials forms an assemblage of which 
the various members are closely connected in these characters. 
So far as facts already known enable us to say, it seems clear 
that of the Marsupials only an individual of Vrichosurus vulpecula 
and the genus Didelphys, and in the latter only occasionally and 
by no means typically, have preserved the earlier condition of 
the mammalian postcaval system as seen in Ornithorhynchus and 
in Lehidna, where the postrenal part of that vein is persistently 
double, being developed out of both collateral veins of the 
embryo*. ‘This condition is, however, fully characteristic of the 
Edentata, which form an assemblage apparently quite as distinct 
in these characters as are the Marsupials. The present com- 
munication to the Society allows me to confirm the data of 
Hochstetter and Hyrtl by fresh examples of species of Dasypodide. 
I may also mention that in two examples of Myrmecophaga jubata 
which I have recently dissected the postcaval vein was double 
postrenally, though I have not made notes of sufficient elaborate- 
ness to permit of a detailed account of the facts in the earlier 
part of this paper. Hochstetter has also stated that MWyrmeco- 
phaga and both of the Sloths, viz. Cholwpus didactylus and 
Bradypus tridactylus, possess the same type of postcaval system, 
and also the Old World Edentate, Janis t. Judged by the con- 
ditions which obtain in the Monotremata, the Edentata are more 
primitive than are the Marsupials. And, moreover, no Edentate, 
so far as is known at present, shows the typical Eutherian con- 
dition of the veins in question. It is a very singular fact that 
among the Marsupials the typical Eutherian condition of the 
postcaval is seen in only one forin (Petaurus tanguanoides) §, just 
as the Hutherian placenta is also seen in only one form. We 
know so little about the Insectivora as regards their venous 
* Morph. Jahrb. xx. p. 362, pl. xv., and in Amer. Journ. Anat. ii. pl. iv. figs. 17, 
21, &c. 
+ Morph. Jahrb. xxv. p, 621. 
{ Hyrtl, Denkschr. Ak. Wien, vi. 1854. 
§ Morph. Jahrb. xx. pl. xxiii. fig. 26. And, according to McClure, in one 
example of Phalanger wrsinus. 'This of course may be an abnormality. 
34* 
