739 



angles a large transverse tributary lying on the ventral side of the right 

 kidney (from which it receives in its turn two longitudinally-disposed 

 factors, .one anterior, the other posterior) which proceeds from the large 

 inter-renal vein, and also a smaller one just })Osterior to this which is 

 derived from the kidney cajjillaries. 



The conformation of the "renal-portal system" in this frog is also 

 interesting. The only venous blood whicli is su})plied to the two kidneys 

 is, as just implied, derived from the venae renales advehentes of the left 

 renal-portal vein which "capillarize" in the left kidney and then commu- 

 nicate by four main branches wàth the large inter-renal. From this 

 inter-renal the venous blood flows by way of the transverse tributary 

 already mentioned direct into the junction of the right renal-portal and 

 posterior cardinal, so that there exists no "renal-portal system" in 

 the substance of the right kidney. The colour of the blood in the 

 several veins conlirms this since blood entering the posterior cardinal 

 by the transverse tributciry (derived both from the left renal-portal and 

 subsidiary veins and from the renal arteries) is distinctly reddish-purple 

 in hue, whereas the blood contained in the large right renal-portal is of 

 a deep blue, this difference of colour clearly showing that none of the 

 more deeply coloured blood enters the kidney substance. This difference 

 in blood-colour is diagrammatically indicated in the above figure [B] by 

 means of the dotted and striped appearances given to the respective veins. 



It remains to be mentioned that all the veins arising from the left 

 pre-caval are normal, the abnormality only affecting the right side of 

 the animal. The considerable size of the persistent right posterior car- 

 dinal, right renal-portal and right pre-caval veins is of course due to the 

 fact that the whole of the venous blood derived from the posterior por- 

 tions of the body is returned to the heart by these veins. 



Though the above abnormality is new as regards the particular 

 mode of persistence of the frog's posterior cardinal, yet, as before stated, 

 it is not the first example of a persistent posterior cardinal having been 

 found in this animal; three such have previously been described, brief 

 accounts of which I will here give for comparison. 



In 1888, Howes (1) described the persistence in a female frog of 

 a left posterior cardinal. This, as in my specimen, was posteriorly con- 

 tinuous with the renal-i)ortal of the same side, but, unlike my specimen, 

 Avas also joined by a transverse branch at the anterior end of the kidney 

 to the post-caval, which vein was present though it was of smaller size 

 than usual; anteriorly, the posterior cardinal joined the pre-caval in the 

 usual manner. This abnormality is represented diagrammatically in fig. 2. 



In 188H, W. N. Parker (2) described another instance of the per- 

 .sistence of a left posterior cardinal in a male frog. This posterior 



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