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Show 1888.] THE CARPUS AND TARSUS OF THE ANURA. 153 goes, as will be shown later, a by no means insignificant range of modification. In no case, however, is it ever segmented into more than three pieces exclusive of its carpal; it thus never bears more than two phalanges. The other four digits bear each, in order of succession from within outwards, 2, 2, 3, 3 phalanges, certain Ranidse excepted (cf. footnote, p. 178). The inner border of the metacarpal of the second digit becomes, in the males of certain Anura, as is well known in the case of the Common Frog, variously crested or tuberculated in connection with the overlying "thumb-pad" (2'. fig. 6), or for support of the horny clasper as in Leptodactylus (** fig. 25). Leydig has recently described these modifications with great accuracy (26), so far as they concern the indigenous European forms. b. Distal Carpal Elements (Carpalia).-In the more specialized forms certain of these unite with each other or with adjacent elements (ex. Hyla, fig. 20, Rhombophryne, fig. 32) ; and for the present we shall exclude such from consideration, dealing only with those feet in which the elements remain permanently distinct. All previous writers are agreed that in such forms five carpalia are represented. While we admit that such may be the case, we doubt, as the sequel will show, the homology of that element which our predecessors, not excluding Born (6). interpret as the carpal of the 5th digit. Carpale 2 (Trapeze of Duges ; Trapezoides of Ecker).-This element ((2) of our figures) is never more than insignificantly displaced. Examination of any one drawing will show that it lies in a line with the head of the 2nd metacarpal (2') ; and comparison of Alytes tadpole (fig. 9) shows this to be its primitive position. It is usually of fair size, becoming well ossified. In the Disco-glossidce it undergoes a slight reduction (rigs. 6 & 7), and this reaches its maximum, amounting to insignificance in the rj of Leptodactylus (fig. 25). Comparison of this carpus with the adult Discoglossus (fig. 6) and the larval Alytes (fig. 9) is sufficient to show that this partial atrophy is to no small extent associated with the specialization and enlargement of its metacarpal. W e have found this element to be free in all but Brackycephalus, Pipa, and Rhombophryne. Carpalia 3 and 4.-In certain forms these two elements become confluent, constituting the nucleus of a large bone (3, 4 k, figs. 25, 26, 28), called by Ecker (17, p. 53) the "capitato-hamatum." In the Discoglossidce, Pelobatidce, and Aglossa, however, carpalia 3 and 4 are distinct. Considering the general affinities of these three families, and that there are combined among them all the lowest terms of structural detail met with in the whole Order, this point of agreement is the more welcome and suggestive. Examination of the figs, which we append will show that in the two first-named families there is a tendency towards an increase in size of the 4th carpal and consequent displacement of the 3rd one (cf. figs. 5, 7, and 18). The two, however, lie, in all, practically in a line with the 3rd and 4 th metacarpals-absolutely so in the |
