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Show 1899.] THE CARPUS OF CTENOMYS. 433 the distal as the metacarpal segment of the postmiuimus."l In his last utterances on the subject2, neither the pisiform and calcaneus, nor the so-called praspollex and prsehallux, are considered as true carpal and tarsal bones, but " they have the same rank and position as the metacarpal and metatarsal bones." What for palaeontologists has been scarcely doubtful from the beginning of the discussion, becomes still clearer by the recent researches, viz., that the Tetrapoda have always been penta-dactyle3; so that we may use " Pentadactylia" as synonymous with Tetrapoda. The remains of supernumerary rays must be traced to stages beyond the tetrapodous. Although a finger (toe) is a ray or part of one, the more general term " ray " (Strahl) is not synonymous with finger (toe); to use the two terms promiscuously is equivalent to deliberately confusing the discussion. "Where we meet among Mammals with an especial development of those supernumerary rays, this condition can always be traced to their secondary adaptation to special functions, as was long ago insisted upon by Winge and others4. As to the pisiform, a more or less ossified distal element seems to be a common occurrence among Rodentia; apart from Bathy-ergus and Ctenomys, I find it in all the species of Mus up to the present examined (pel. fig. 4), including Mus decumanus and Mus alexandrinus; it is present too in Brachyuromys ramirohitra and in Arvicanthis niloticus (tig. 5, pd.). In all of these its special development is apparently due to an adaptation to either climbing or fossorial functions (to the latter in Bathgergus, Ctenomys, Mus nativitatis), or to both combined. The so-called os Daubentonii of the Gibbon, about which more will be said farther on, is according to an observation by Leboucq, the most proximal part of the Mammalian pisiform ; from its position it cannot be considered as an " ulnare antebrachii " (Thile-nius); but seems to be the only part of the pisiform belonging to the carpus. 1 P. Z. S. 1889, p. 260. 2 P. Z. S. 1894, p. 373.- ' Hand und Fuss,' p. 312. 3 Cf. e. y. Emery, in Semon's ' Forschungsreise,' ii. p. 399 (1897): " Die Zahl der echten Finger und Zehen ist und war immer auf 1'iinf beschrankt." 4 In his " Beterat" (p. 336), von Bardeleben admits that this may be the case with the "praepollex" of Pedetes, although on a preceding page the same had been adduced as a convincing argument in favour of his case: "... drittens suchte Bef. nach Saugetieren, die nicht nur das Rudiment eines Praepollex, sondern einen ' wirklichen Finger' batten-im Sinne Geyeubaur's, der dai'iir ein Metacarpale und einige Phalangen verlangt. " Nach dem alten, so recht fur den Wahlspruch eines Naturforschers geeigneten Worte : ' Suchet, so werdet ihr finden,' gelang es damals (1889) auch, nicht nur bei Reptilien, fossilen und lebenden Schildkroten u. a. einen Praepollex und Prsehallux uachzuweisen, sondern sogar Sduyetiere zu finden, bei denen der Praepollex (Pedetes capensis), oder der Postminimus (Bathyeryus maritimus) aus zwei Knocheubestekt . . . .Pedetes besitzt aber nicht nur zwei Knochen im Pras-pollex- ekelet, sondern einen wirklichen ' Finger' mit einein breiten, fein-gestreit'ten Xagel, mit Falz etc., wie Bef. fur die drei Londoner Exemplare festgestellt hat! " (/. c p. 283). |