| OCR Text |
Show 1889.] CARDINAL VEIN IN THE FROG. 147 Howes (except that there was no anastomosis with the renal portal), could be seen opening into what appeared to be the inter-renal portion of the postcaval (r.cd). Upon further examination it was found that there was no postcaval trunk extending from this inter-renal vessel to the heart, and the apparent azygos was thus the completely persistent left posterior cardinal. The renal portion of the right cardinal must therefore have fused with its fellow in the usual manner to form the large median vessel, which ordinarily gives rise to the posterior part of the postcaval, while its anterior part disappeared, although the hepatic portion of the postcaval remained undeveloped. The left cardinal, united with the renal portion of the right, had thus to serve as the channel for all the blood from the posterior extremities, &c, except that which entered the liver by the anterior abdominal vein, which had the usual relations. The hepatic veins (h.v) opened directly into the sinus venosus. The spermatic vessels (sp) were very asymmetrical, as were the ovarian vessels in Howes's specimen. Hochstetter states that the hepatic portion of the postcaval remains undeveloped exceptionally in the Salamander, in which case either one or the other cardinal becomes correspondingly enlarged. It is known, too, that in M a n the lower portion of the left cardinal is occasionally present, and that the postcaval sometimes remains undeveloped, the blood being returned to the heart by a persistent posterior cardinal, in which case the hepatic veins open independently into the right auricle *•. It is extremely interesting to find these exceptions to the rule that all air-breathing animals (Amphibia and Amniota) possess a postcaval, and they seem to completely support Hochstetter's views as to the mode of formation of the postcaval. The observations described and referred to above have helped me considerably in the determination of the homology of the two veins in Protopterus which have usually been described as venae cavee pos-teriores. At the time when m y paper " Zur Anatomie und Physiologie von Protopterus annectens " 2, giving a preliminary account of the work on which I am still engaged, was published, 1 had made only a very cursory examination of the veins, and this had led me to the conclusion that " das was man bisher bei Dipnoern als Vence cavee posteriores bezeichnet hat, sind sicherlich keine solchen, sondem entsprechen den (allerdings einigermassen modificirten) Vence cardinales posteriores." Owing to the extreme difficulty in following out the venous system in preserved specimens of Protopterus, I have not even yet completely satisfied myself as to the exact relations of all the vessels. But since the above-mentioned paper appeared, I have succeeded in elucidating some important points which were then by no means clear. Dr. Hochstetter has recently been good enough to make several 1 Quain's Anatomy, 9th ed. vol, i. pp. 514, 518. 2 Berichte der naturforschenden Gresellschaft zu Freiburg i. B., IV. Band, 3 Heft. See also ' Nature,' vol. xxxix. 188S, p. 9. |
