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Show 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, the remains of the anterior part of the right cardinal. The renal-portal veins (r.p) are connected with a single caudal vessel (c.v). 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 postcaval respectively. Hyrtl's account of the venous system in Lepidosiren paradoxa1 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 vense 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 Protopterus. A still further modification of the cardinals appears to have taken place in Ceratodus. Dr. Gunther2 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. xii. fig. 3), and also, as in fig. 2, pi. xii., 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. xii., 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, 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 corresponds 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 bohm. Gesellschaft der Wissenschaften in Prag, 1845. 2 Description of Ceratodus. Phil. Trans, vol. 161 (1871). |
