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Show 1889.] CARDINAL VEIN IN THE FROG. 149 Hochstetter's discovery concerning the paired connection between the cardinals and hepatic veins in certain Elasmobranchs, they confirm his general views as to the development of the postcaval in other types. M y statement concerning the two veins in Protopterus which take their origin in the kidneys and also receive blood from the body-walls and generative organs was only partially correct: that is, it was correct so far as the left vessel and the renal portion of the right one are concerned. There can be little doubt that the vein of the left side corresponds entirely with the left posterior cardinal of Fishes (fig. 2, p. 148, Led). It extends along the ventral surface of the kidney, partially imbedded in the lymphatic tissue which surrounds that organ, and then passes along the dorsal border of the corresponding gonad, between the latter and the lung, to enter the precaval, being packed in by lymphatic tissue all along its course. The vein of the right side (pt.c) is considerably larger than that of the left (/. cd), and as it passes along the kidney it is connected with its fellow by three or four transverse anastomoses. A similar asymmetry of the two cardinals is very common amongst Fishes, and there seems often to be a tendency for one or the other to become obliterated, as occurs to a greater or less extent with such remains of them as may persist amongst the Anura and Amniota. The liver (Ir) of Protopterus abuts closely against the anterior end of the right kidney (k), and at this point the right cardinal (pt.c2) is continuous with a vein (pt.cf which passes forwards imbedded in the dorsal border of the liver, from which it emerges anteriorly and turns medianwards so as to extend for a short distance as an independent vessel, which perforates the pericardium in the middle line to enter the sinus venosus. The liver is supported by a net-like peritoneal fold, which is connected with the mesogastrium and is continued on to the vein in its independent portion. This *f Ilohl-venengekrdse " is characterized, according to Hochstetter *-, as being the bearer of the independently developed portion of the postcaval. The number and arrangement of the hepatic veins (h.v) is rather curious. In several specimens examined there were one or two large ones entering the main vein just before it becomes free from the liver anteriorly, but besides these there are numerous small vessels all along the course of the vein through the liver. These facts seem to prove conclusively that the right vein described above is a true vena cava inferior, which is made up of the renal section of the right cardinal and of an independently formed hepatic portion. In fact, the figure given by Howes (loc. cit.) of the veins of a Frog in which the left azygos persisted resembles very closely the state of things in Protopterus, except that the fusion of the renal section of the two cardinals does not take place, but only a reduction of that of the left side, and its connection with what must now be called the renal portion of the postcaval by transverse anastomoses. 1 " Ueber das Gekrose der hinteren Hohlvene," Anat. Anzeiger, iii. Jahrgang, 1888, p. 965. PROC. ZOOL. Soc-1889, No. XI. 11 |
