OCR Text |
Show 160 PROF. G. B. HOWES AND W. RIDEWOOD ON [Mar. 6, Order, the Anura would appear to be unique among all living animals in that they possess, without exception, a double centrale carpi. h. Compound structures resulting from the fusion of two or more Carpal elements.-Under this head we have designated certain large bones, met with only in the adults of the more specialized families and in some few isolated genera. There can be little doubt but that the great development of our postaxial centrale (k) is associated with the peculiar " tread" of the fore foot of the Anura and with the remarkable distortion which the parts of this limb have undergone. In the compound structures now to be dealt with, this postaxial centrale forms as it were a central nucleus, towards which one or more adjacent elements become drawn and with which they amalgamate. The fact that the resulting compounds may occur independently in different families is sufficient to show that they are, for the most part, of nought but physiological significance. Capitatum.-We suggest this term l for the simplest of the above-named structures. It occurs in Pelodytes (fig. 11) and Pseudophryne (fig. 22) (4 k), being formed, as shown, by the confluence of the postaxial centrale and the 4th carpal. Capitato-hamatum.-This term was applied by Ecker (see infra) to a large bone which, in the Edible Frog (3. 4. k, fig. B, woodcut, p. 174), carries the 3rd, 4th, and 5th digits. It is formed by the confluence of our capitatum with the third carpal. W e have observed it in the Ranidce, Dendrobatidce, Engystomatida?, Cystignathidce, Bufonidce, Hylidce, and certain others ; it is not present in either the Discoglossidae, Pelobatida?, or Aglossa. It often sends up, especially in old individuals, a process along the outer face of the ulna (ex. Leptodactylus, fig. 25) for muscular attachment. This lobe is absent in the tadpole, and, from its function, it need hardly he said that it has nothing to do with articulation upon the forearm 2. There sometimes runs along the under surface of this bone a longitudinal groove, which terminates posteriorly, in a line with the interspace between metacarpals 3 and 4. In old specimens this becomes converted into a tubular perforation, which will admit a bristle and transmits the ramus lateralis of the ulnar nerve 3. On examination of the adult carpus, doubts might be refisonably entertained as to whether both third and fourth carpalia were incorporated in this piece. Apart, however, from the fact that in the young animal their boundary lines are definable, there is a feature of some interest in its mode of attachment. In Hyla ccerulea (fig. 20) and Nototrema there still remains that ligament which, in the simpler forms, passes between the 4th carpal and the head of the 5th metacarpal; true to its relationships, it arises on a level with the head of metacarpal 4 (cf. Xenophrys, fig. 14), and it differs from 1 Uniformly with Ecker's capitato-hamatum (17, p. 53). 2 As might at first be imagined, from Wiedersheim's fig. oi[Bufo (36, pi. 211. fig. 177), in which this feature is grossly exaggerated. 8 Cf. Ecker and Wiedersheim, ' Anat. d. Frosches,' part ii. p. 40 and fig. 14. |