740 



cardinal was continuous jDOsteriorly, not with a ronal-portal but directly 

 with the inter-renal vein, and thus in this region was equivalent to, and 

 doubtless homologous with, a true post-caval; anteriorly, the posterior 

 cardinal entered the left pre-caval, as indicated in fig. 3 — this mode 

 of termination of the anterior extremity of the vein alone indicating its 

 posterior cardinal nature. According to Parker, Howes found another 

 example of a variation identical with that which he before described, 

 save that the left persistent posterior cardinal opened into the left sul)- 

 clavian instead of into the left pre-caval — which statement I presume 



Fis. 2. 



Fier. 3. 



Fig. 2. Persistence of a left posterior cardinal vein in a frog. Post-caval vein also 



present. ! Modified after Howes.) 

 Fig. 3. Similar abnormality in a frog. Post-caval vein absent, except as an inter- 

 renal vein. (Modified after W. N. Parker.) >S, subclavian; P. F.C, posterior vena 

 cava ; L.P. C\ left posterior cardinal. 



merely means that the junction of the posterior cardinal Avas situated 

 further to the left of the heart than usual. 



Part II. 

 A Suggestion as to the Phylogenetic Origin of the Posterier Vena Cava. 

 AVhilst pursuing some enquiries into the subject of the "Renal 

 Portal System'*, I was incidentally led to consider the possible reason 



