1909.] POSTCAVAL VEIN IN MAMMALS. 513 
remain of the double postcaval*, The Edentata, Insectivora, and 
Carnivora can be arranged in a series in the order in which they 
have just been named in respect of the double character of the 
posteaval veins, 2. e. the more or less complete persistence of both 
of the subcardinal veins or cardinal collateral veins. It is doubt- 
less important to note that the Rodentia, which are equally 
primitive in the azygos veins, show no traces of any likeness to 
the Insectivora in respect of the postcaval. 
The condition characterising the adult Centetes and Dasypodidee 
is also very well seen as a temporary feature of the foetal Mole. 
Ata certain stage figured by Messrs. Soulié and Bonne 7, there 
are two thick veins which unite inferiorly and which I presume 
represent the cardinal collaterals as described by McClure. A 
small branch of the renals which is not lettered by these authors 
seems to correspond to the real cardinals. Between the preserved 
cardinal collaterals (in the 12°5 mm. long embryo described by 
Soulié and Bonne), which are thick veins, is a medianly situated 
single vein of some calibre, which may perhaps be the equivalent 
of the subcardinals as described by McClure in the American 
Opossum, or possibly be the equivalent of the median prolongations 
of the commissural vessels in Centetes. This soon disappears as 
an important vessel, but remains as a slight commissure. ‘The 
authors speak of the persistent postcaval as being formed in the 
postrenal region by the ‘right internal vein of mesonephros,” 
which is not homologised with any particular division of cardinals. 
There seems also at a certain stage to be a caudal plexus which 
heightens the likeness to the adult Armadillo, The developmental 
phenomena argue at least a general similarity with other Mammals 
as described by other authors. 
As to the Ungulata, I have examined the postcaval and its 
branches in several examples of Hyrax capensis and in one of 
H. dorsalis. The general arrangement in both species appears to 
be as follows :—The renals are asymmetrical as usual, the right 
opening into the postcaval above the left. The postcaval post- 
renally lies as usual to the right of the aorta. The ovarian vein 
on the left side opens into the renal, but on the right into the 
postcaval in line with the orifice of the left renal. There is thus 
a kind of symmetry between the two ovarian veins such as is 
met with in the Rodents, some Carnivores, &e. In one specimen 
(of capensis) I noted more particularly the branches of the right 
ovarian vein. This vein shortly after leaving the postcaval (it 
is simpler for purposes of description to disregard the direction 
of the blood-flow and to treat these affluents as branches) divided 
into two equisized veins. The anterior of these was directed 
forwards and ran along the body-wall giving off branches to 
the parietes. It ran about parallel to the postcaval and its 
course suggests an anterior section of the postcardinal. The 
* See Beddard, P. Z. S. 1909, p. 491, text-fig. 131. 
+ “Recherches sur le développement du systéme veineux chez la taupe,” Journ. 
de V Anat. et Phys. xli. 1905, p. 1. 
