Sprencer— Zhe Blood Vessels of Ceratodus. 31 
inferior vena cava in Amphibia. Subsequently to the formation of the two 
posterior cardinal veins ¢he anterior part of the inferior cava ts found independently 
of but soon unites behind with the right posterior cardinal vein. In the Amphibia the 
two cardinals unite backwards for some distance to give rise to the posterior section 
of the vena cava inferior between the two kidneys. This long union does not obtain 
in Ceratodus where the kidneys are placed very posteriorly and the reproductive 
organs are long band-like structures stretching a long distance forwards. They 
unite, however, between the kidneys where the venz renales revehentes enter. 
In Ceratodus, further, the two vessels which on each side open into the single 
large vessel between the kidneys must be regarded as vene renales revehentes, which 
earry back from the kidneys blood taken to the latter by the posterior trunk, the 
iliac, and the intercostal veins. 
Except for the more posterior point of fusion of the two cardinals, Ceratodus 
presents us with a condition closely comparable to that seen, according to Gotte, 
during the development of Amphibia. In the latter the anterior portions of the 
cardinal veins atrophy whilst in Ceratodus the left persists throughout life and a 
remnant of the right remains, carrying back blood from the vertebral and costal 
region in the anterior part of the trunk. In this way Ceratodus presents a 
remarkable union of piscine and amphibian characters. 
The anterior abdominal system, as described previously, is again one of the most 
striking features in the venous system of Ceratodus. Whether or no the vessels 
described here as pelvic are homologous with the lateral veins of Elasmobranchs 
they have the same relationship to the vein of the hind limb of Ceratodus as have 
the pelvic in an amphibian to the femoral veins. Gdtte, again, has described the iliac 
vein in the development of Amphibia as uniting at first both with the median vessel 
formed by the posterior union of the cardinals-and also with a longitudinal vessel 
on the outer border of the kidney. The latter union is strikingly similar to the one 
(fig. 19) which occurs in the case of the hind limb vein in Ceratodus. The latter 
vessel divides into two of which on each side of the body one runs forwards, unites 
with its fellow and then the median vessel thus formed runs forwards to open into 
the sinus venosus. The median vessel is distinct though comparatively a small one 
and its formation by union of the pelvic veins and subsequent entrance into the 
sinus venosus prevent our regarding it as the homologue of the ventral cutaneous 
vein in Elasmobranchs. In Amphibia the anterior abdominal vein is at first a double 
one, each part entering the sinus separately and though there is no trace anteriorly, 
in the adult Ceratodus, of this double nature, still its origin and termination 
justify us in applying to it the name of anterior abdominal. 
