Spencer — Zhe Blood Vessels of Ceratodus. 25 
It may be noticed, however, that in contrast to what obtains in such forms as 
Raja, Squatina, Squalus, Spinax, and Mustelus,* che caudal and posterior cardinal 
veins are directly continuous and that though a renal portal system is formed this 
does not intervene, in Ceratodus, between the two veins mentioned. We have, in 
fact, a renal portal of the amphibian type existing side by side with a posterior 
cardinal system of a primitive piscine nature. 
(2) Lnferior vena cava (figs. 10 and 16). 
In Dr. Giinther’s brief account, he described the vessel now under consideration 
as a single “vena cava posterior.”+ The vessel called above the posterior cardinal 
of the left side he, however, described as ‘a very strong vein from the left testicle, 
which corresponds in situation and function to the main trunk and might be called 
a left vena cava posterior ; but the currents of blood in the two run in opposite 
directions—that of the right (main) trunk running towards the head, that of the left 
towards the tail.” It will be seen that this account corroborates his with regard to 
the right or main trunk, and differs from him with regard to the left. 
The right branch of the caudal vein is a very large one—the largest vessel 
indeed in the body of Ceratodus: it passes from the anterior end of the kidney 
directly into the testis (or ovary), which is shorter on the right than on the left side 
(fig. 16). Both vein and artery, instead of, as on the left side, passing on to the 
anterior end of the body cavity, dorsad of the liver, run directly from the testis into 
the elongated right lobe of the liver. In this the artery runs forwards and then 
turns dorsalwards to join the cceliaco-mesenteric artery just before it gives off the 
enteric branch to the intestine. 
The vein runs straight through the substance of the liver receiving in its course 
(fig. 17) many small branches: reaching the median part it opens directly into the 
sinus venosus by a wide aperture on either side of which lies the opening of one of 
the hepatic vems. Its course from between the kidneys and then forwards through 
the body cavity and finally through the substance of the liver into the median part 
of the sinus venosus, as well as its relationship to the hepatic veins are unmistakable 
points of resemblance between it and an inferior vena cava typical of Amphibia. 
(3) Vertebral vein of right side (figs. 8 and 16, 7. vert. v.). 
This is evidently a vein recognised by Dr. Giinther, who says “the second 
artery ” (z.e., of the left side, the brachial artery of the above description) “forms a 
* Parker, loc. cit. p. 704. 
+ Loc. cit. p. 539. 
D 
