CARPUS AND TARSUS
In Ascaphus (Ritland, 1955a; cleared and stained specimens of nearly grown males) distal carpals 1, 2, 3 and 4 are present and separate, increasing in size in the order given (Fig. 9). A prepollex rests against centrale 1; centralia 2 and 3 are fused; the radiale fuses with centrale 4, and the intermedium fuses with the ulnare; radius and ulna are fused with each other as in other frogs. The digits (and metacarpals) are considered by Ritland to be 1-4, in addition to the prepollex, rather than 2-5.
Fig. 9. Skeleton of fore foot of Notobatrachus (after Stipanicic and Reig, 1956, terminology revised) and Ascaphus (after Ritland, 1955 a); all ×5. For explanation of abbreviations see Fig. 3.
In the Jurassic Notobatrachus Stipanicic and Reig (1956) have shown the carpus with surprising clarity (Fig. 9). If their nomenclature of the parts be revised, we obtain a fairly close resemblance to Ascaphus, except that centralia 2 and 3 are not fused, distal carpals 1 and 2 do not show (which would easily be understood if they were of the size of those in Ascaphus, or not ossified), and the intermedium remains separate from the ulnare.
In Salamandra (Francis, 1934; Nauck, 1938) distal carpals 1 and 2 are fused in both larva and adult, and 3 and 4 are separate; the radiale, intermedium and ulnare are separate in the larva but the latter two fuse in the adult; centrale 1 (labelled prepollical cartilage by Francis) and centrale 2 are separate. Francis considers the digits (and metacarpals) to be 1-4. Apparently the arrangement here indicated for the larva is characteristic of other larval salamanders, except where further reduced, and reduction below the number given for the adult is common in other terrestrial forms. The radius and ulna are, of course, separate.
The ossification of carpals is more likely to be complete in adult frogs than in salamanders, but some ossification of all parts named is found in several of the latter. A common ancestor of frogs and salamanders could be expected to have the following elements present and ossified in the adult: distal carpals 1-4 separate; 3 centralia; radiale, intermedium and ulnare separate. Comparison with fossils older than Notobatrachus is fruitless on these points, unless we go back to forms too distant to have any special value, such as Eryops. This is because of inadequate preservation and because the elements are not fully ossified in many immature specimens.
For the purpose of this review there is no special value in a comparison of the tarsi of frogs and salamanders, since the leaping adaptation of the former leaves very little common pattern between them. Even in Protobatrachus, where the legs were not yet conspicuously lengthened, the tibiale and fibulare ("astragalus" and "calcaneum" respectively) were already considerably elongated. The carpus and tarsus of Amphibamus are as yet undecipherable.