150 ON THE LEFT CARDINAL VEIN IN THE FROG. [Mar. 19, 
I have not. been able to find any trace of a right azygos, that is, of 
the remains of the anterior part of the right cardinal. 
The renal-portal veins (7p) are connected with a single caudal 
vessel (cv). They receive a pelvic vein (p.v) on either side as 
well as the posterior veins from the body-walls and generative 
organs, the anterior ones passing into the left cardinal and post- 
caval respectively. 
Hyrtl’s account of the venous system in Lepidosiren paradoza* 
agrees in many points with the above description, although he 
regards the left cardinal as a left vena cava posterior. He, however, 
states that the caudal vein is paired, and that there is a paired 
azygos running alongside the aorta in addition to the two main veins 
which he describes as ven cave posteriores. It seems unlikely that 
such an accurate observer as Hyrtl should have been mistaken in his 
observations, and I can only suppose that if the paired ‘‘ azygos” 
is present, it is not a true azygos, but an independently formed vessel, 
for there can be little doubt that the left ‘vena cava posterior ”’ is 
the left cardinal, as its relations are so similar to those seen in 
Protopterus. 
A still further modification of the cardinals appears to have taken 
place in Ceratodus. Dr. Giinther? states that a single large vena cava 
posterior is present, collecting the blood from the trunk, tail, and 
abdominal organs, except the lungs and intestine. The position 
and relations of this vessel are apparently similar to those of the 
postcaval of Protopterus, except that the caudal vein is said to enter 
it directly. Unfortunately, Giinther’s figures do not show the entire 
course of the vessels described, and it is therefore impossible to judge 
of their exact relations. But as a renal-portal system is present (see 
pl. xli. fig. 3), and also, as in fig. 2, pl. xli., the ‘‘ caudal vein’’ is 
shown to enter the postcaval from the body-walls by an anterior and 
posterior factor so far forwards, I cannot help thinking that the vessel 
described as the caudal may be simply a large vein from the dorsal 
body-walls, and not the true caudal. I may add that in fig. 3, 
pl. xli., a median and two lateral veins are shown entering the 
renal-portal system, and these, although not described, have very 
similar relations to those of the candal and two pelvic veins of 
Protopterus. The hepatic veins are numerous, as in Protopterus. 
In enumerating the vessels which open into the postcaval, Dr. 
Giinther mentions “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.” According to 
this description, it appears that the anterior part of the left cardinal 
has disappeared, and that Giinther’s left vena cava posterior corre- 
sponds to its persistent renal portion, which now appears simply as a 
factor of the postcaval. If this is the case, we can compare the 
condition of the postcaval and cardinals to that found in most Anura, 
1 Abhandlungen der béhm. Gesellschaft der Wissenschaften in Prag, 1845. 
? Description of Ceratodus. Phil, Trans. vol. 161 (1871). 
