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Show 166 PROF. G. B. HOWES AND W. RIDEWOOD ON [Mar. 6, the head of the outermost metacarpal, especially in Xenophrys, in the adult of which it carries a distinct bony element (5, fig. 16), regarded by us as a 5th carpal (p. 154). It'is worthy of remark that in its mode of ossification this element conforms in every detail to that observed for the other capalia. Born asserts that he found (6, p. 63) in a Pelobates larva a centrale carpi, identical with that figured by him in the young of Alytes; and he expresses his doubts as to whether the same does or does not regularly fuse with the 5th carpal (our postaxial centrale, k) in the adults of both genera. It must suffice to point out that we have not here observed the presence of that cartilage which he calls the centrale, and the statements already made by us for Alytes (p. 158) apply equally to this genus. This preaxial centrale (naviculare, n) may or may not reach the radius in individuals of a species. In the Pelobates figured (fig. 18) it is represented as nearly touching that bone, but in the other carpus it did not extend more than halfway towards it. W e have already stated (p. 159) our reasons for regarding this ascending lobe of the naviculare as purely secondary. Extremes of modification of the pollex are met with within the limits of this small family. In Pelobates and Xenophrys it consists, excluding its carpal (po. i.), of a small styliform structure which is quite unsegmented; in Pelodytes, on the other hand, it is very large and swollen (fig. 11, po. i.-iii.) and definitely segmented. In all three genera the rotation of the hand upon the fused radius and ulna is verv marked ; and in Pelodytes this reaches its maximum, having gone on through more than a right angle (fig. 11). Comparison with the other two genera suggests that the great development of the pollex may be in some way associated with this distortion ; and we are inclined to ascribe to the same cause a distinct ossification of the distal extremity of the ulna here met with (* of fig. 11) l. In Pelodytes the carpus is exceptional among those of this family, owing to the fusion of the postaxial centrale and fourth carpal to form one bone, the capitatum (4. k, fig. 11). Hind Foot (figs. 12, 13, 17). It is interesting, in the light of the facts concerning the fore foot, to note that the extremes of modification undergone by the astragalus and calcaneus in the Anura are exemplified in this family. In Pelodytes (fig. 12) they are confluent for their whole lengths, much elongated and slender in the middle ; in Pelobates they are relatively shorter than in any Frog which has come under our notice. Xenophrys is, in respect to relative length, intermediate between the two. The calcar (pre-hallux) attains, as is well known, its maximum development in this family. Rosenhof first described and figured 1 This is not received by the ulnare, as might appear on examination of the figure ; it lies, in life, ventrally to the line of junction between that bone and the lunatum. It breaks away with great readiness, so much so that we originally imagined it to be a distinct element. |
