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 {r.p) are connected with a single caudal 

 vessel (c.w). 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 paradoxal 

 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 venae cavse 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 

 Protoptej'us. 



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 

 pi. xli. fig. 3), and also, as in fig. 2, pi. 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, 

 pi. 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 caudal 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, tbatof 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, 



' Abhandlungen der bohm. Gesellschaft der Wissenschaften in Prag, 1845. 

 - Description of Ceratodus. Phil. Trans, vol. 161 (1871). 



