360 



to form the inter-renal portion of the posterior vena cava. The ante- 

 rior half of the latter is formed by a separate vein fusing with the 

 inter-renal vein. Later, the two outei' parts i. e. Jacobson's veins 

 receive the iliacs and so form the renal portals of the adult. The 

 caudal vein disappears, as do also the anterior parts of the posterior 

 cardinals. 



In an animal like the frog where the tail is so reduced in the 

 adult, it is only to be expected that the caudal vein and the first part 

 of the bifurcation to form Jacobson's vein should not often be found; 

 and this probably accounts for the fact that my Specimen B is the 

 only case on record with these veins still persisting. The renal portal 

 is then composed of two distinct parts ; an anterior formed from Ja- 

 cobson's vein, and a posterior formed from the iliac vein. The anterior 

 portion of the loop round each kidney on the other hand, more fre- 

 quently persists; and moreover, its persistence is sometimes correlated 

 with an entire absence of the anterior part of the post-caval as we have 

 exemplified in five cases, viz; those described by Parker (16) and 

 Woodland (22) and the three included herewith. The conformation 

 of the inter-renal in these abnormahties, noticeably in Specimen C of 

 the preceeding, is thus readily explicable. 



Shore (20) points out that the anterior part of the post-caval 

 arises as a vascular connection between the liver and the right posterior 

 cardinal. This connection throws an interesting light on the only ab- 

 normality described by Howes (10) in which there is a persistent 

 posterior cardinal together with a post-caval, for it is the left posterior 

 cardinal that remains, and the right that has disappeared anterior 

 to the liver connection. 



There are, in the consideration of these abnormalities of the venous 

 system, two points of which, up to the present, I have been unable to 

 find a satisfactory explanation. The first is the absence of the venae 

 renales advehentes in some of the cases, where Jacobson's vein per- 

 sistes, already referred to in the description of Specimen A. 



The second is the fact that in all nine specimens of abnormalities 

 in connection with renal- portals, post-cavals or persistent posterior 

 cardinals there is only one, that of Howes (10) in which the animal 

 was a female and, strangely enough, this is the only example in which 

 there is both a post-caval and a posterior cardinal. Such a pre- 

 ponderance of males, which seems beyond mere coincidence, appears 

 to suggest that there may be a correlation between this sex and the 

 presence of abnormalities in these particular veins. 



