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Show 1 78 PROF. G. B. HOWES AND W. RIDEWOOD O N [Mar. 6, 7. That the naviculare is a centrale and not the basal segment of tbe pre-hallux. 8. That the pre-hallux never consists of more than four pieces, and that it conforms to the structural requirements of a sixth digit. 9. That the outer free border of the pre-hallux may undergo a process of fragmentation, giung rise to insignificant nodules of cartilage indistinguishable from those for which, in certain other Vertebrata, the value of lost rays has been claimed ; and that the grounds upon which this claim is based are unsatisfactory. 10. That there is a tendency towards loss of independence of the hallux-tarsal in the Discoglossidce, Pelobatidce, and some Ranidae, that element in them remaining cartilaginous and small, or fusing with one of the adjacent elements. 11. That Pipa is alone exceptional among living forms, in that the third digit exceeds the fourth one in length. Perusal of the body of this paper will show that in all the higher families of Anura there is a general tendency towards confluence of three or more of the carpal elements, but consideration of the fact that such modifications by fusion may not be even genericallv constant, shakes our faith in them as guides to affinity. The fact which stands out most conspicuously is that the least modified conditions of both fore and hind feet are most nearly combined in the Discoglossidae. Hochstetter has recently shown (20) that in Bombinator the posterior cardinal veins are retained for life, in a slightly modified form, and his observation has been supplemented by one of us and extended (22) to Alytes mid Discoglossus. Adding these facts to those so well known concerning the vertebral and other characters of this family, there can no longer be any doubt that its members are, by far, the least modified of all living Anura. The digital formula of the Anura is l:- Fore. Hind. Ph. 2, 2, 3, 3. Ph. 2, 2, 3, 4, 3. The only other Amphibia of which we have any knowledge whose phalanges approach this in order of arrangement are the 8tegocephalia of the Permian. W e unfortunately know nothing of their carpus and tarsus. Baur has lately tabulated (1, p. 64) the digital formulae of all known Urodela, and perusal of his tables wrli show how completely all the members of that order are, in this respect, modified as compared with the Anura. Thus it is seen that while the limb-skeleton of the Frogs and Toads is specialized in the extreme for physiological purposes, there is retained in it a leading morphological feature which carries us back to some of the oldest known representatives of the class Amphibia ; aird we must look to the Stegocephalia themselves or to some closely allied forms fur the ancestors of these familiar creatures. 1 During the passage of these pages through the press, Mr. Boulenger has called attention (see below pp. 204-206) to the fact that in certain Banidm a supernumerary phalanx is intercalated between the penultimate and terminal ones of each digit in both fore and hind feet. The formula of these animals is thus: 3,3,4,4. 3,3,4,5,4. |
