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.
[Illustration: Fig. 9. Skeleton of fore foot of _Notobatrachus_ (after
Stipanicic and Reig, 1956, terminology revised) and _Ascaphus_ (after
Ritland, 1955 a); all x5. 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.