30 Macteay Memoriat Vouume. 
The caudal vein passing forwards runs downwards to the kidneys between 
which it divides into two main branches running forwards one on either side of the 
mid line. It receives from the kidney two branches on either side which carry to it 
the blood from the renal portal circulation. 
This direct connection between the caudal vein and vessels which must be 
regarded as derivatives of the posterior cardinal system is a feature calling to mind 
the embryonic stages of Amphibia and Elasmobranchs and the adult condition in 
Cyclostomes. 
As shown previously the left forward-running branch receives blood from the 
reproductive glands and runs on to open into the Ductus Cuvieri of its own side. 
The right vessel is, however, much larger than the left, runs forwards nearer to the 
middle line and finally passes through the substance of the liver receiving small 
branches from this and then ofens into the sinus venosus between the two hepatic 
veins. Professor W. N. Parker,* in dealing with Protopterus has stated that the 
vessels which have hitherto been described as “ venze cavze posteriores” are not such 
but correspond to modified “venz cardinales posteriores.” In Ceratodus Dr. 
Giimther spoke of the vessel of the right side as a vena cava posterior and in doing 
so he was, I think, perfectly correct. At the same time it may, I think, be said 
that 2 Ceratodus we have both a posterior cardinal vessel and a posterior (or inferior) 
vena cava present. It is true that the vessel, called in the previous account the left 
posterior cardinal, lies deeper in the body cavity than it normally does in fishes but 
this comparatively slight modification in position is not sufficient to outweigh the 
evidence of its posterior connection with the caudal vein, its relation to the kidneys 
and its anterior termination in the Ductus Cuvieri. 
The vessel of the right side to which the name of inferior vena cava is here given 
presents greater difficulty in the determination of its homology but, judging from 
its relationship to the caudal vein and to the kidney and reproductive organ of its 
own side (identically the same as in the case of the left vessel), together with the 
remarkable course of its anterior part through the liver and its subsequent entrance 
into the middle of the sinus venosus between the hepatic ves, we are forced to 
regard it as the representative of the inferior vena cava of Amphibia (or other forms), 
which has been developed in close relationship to the right posterior cardinal vein. 
It appears as if in Ceratodus, as also in Pisces generally, the right posterior cardinal 
became much larger than the left and as if in Ceratodus it became in part modified 
to form the inferior vena cava. It is interesting to note in this connection the 
account given by Gitte (according to Balfourt) of the development of the 
* Loc. cit. p. 19. 
+ Embryology (Memorial edition), Vol. III. p. 655. 
