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Show 480 AN ABNORMAL VERTEBRAL COLUMN OF THE BULL-FROG. [June 5, This piece, taken by itself, as we have seen, shows very little asymmetry-it is quite similar to the Python's vertebra figured by Bateson, and his description (p. 105) and explanation would equally apply here. But we see that, in the Frog, no asymmetry of the entire column results. It would, no doubt, be too laborious to count the entire number of ribs in a Python, but the suggestion may be made that the apparent " partial division " on one side (fig. 10, II., of Bateson) may be due to the same cause as I suggest above, and that it might be " rectified " further back by another half on the opposite side. He mentions, however, that the 185th vertebra of this same Python "had a similar doubling of the right side," so that, no doubt, he would have observed any corresponding doubling on the left side if it had existed. In his paper on abnormal Frogs' vertebrae, just mentioned, Howes refers to the rarity of the "fusion"of the eighth aud ninth in R. esculenta, so that it seems worth while to add to his specimens two others which I have met with ; whereas Adolphi1 found only one such case in 212 Toads examined, I have met with two cases in eight skeletons of R. mugiens (exclusive of the abnormal specimen just described). In each of these two skeletons, in fact, the conditions of the sacral and eighth vertebrae are precisely those described and figured by Howes on p. 269 (figs. 1 cc, 1 b, 1 c), and, as there, m y specimens present the slight ridge at the line of fusion. It seems, then, that R. mugiens presents great scope for Mr. Bateson : various kinds of " variations " occurring evidently with considerable frequency. Having met with these instances, it seemed desirable to look over the skeletons in our Museum, so as to note auy other abnormalities in the vertebral column which might be presented by them. I was rewarded by finding two cases in species of Toads. The first case occurs in a dried skeleton of Bufo agua, in which the " atlas " is co-ossified with the second vertebra. The second and more remarkable case I noted in B. pantherinus. Here the seven anterior vertebrae are perfectly normal, but the eighth and ninth are united with one another, and the latter with the urostyle (see fig. 16, nat. size). The transverse process of the eighth is fairly stout, that of the ninth is, as usually the case in the genus Bufo, very considerably expanded; whereas the union of the eighth and ninth centra is indicated by " Howes' ridge," there is no indication of the junction between ninth and the urostyle, the centrum is here quite smooth. The sacral transverse process is continuous with the lateral flange or ridge of the urostyle, and there is no " coccygeal foramen " for the tenth spinal nerve, such as usually occurs, the last perforation being just behind the enlarged transverse process. Similar instances of fusion of the ninth vertebra with the urostyle 1 Adolphi, Morph. Jahrb. xix. p. 320. |