| OCR Text |
Show 1888.] THE CARPUS AND TARSUS OF THE ANURA. 161 that of this genus only in that it holds the heads of metacp. 5 in apposition. In its mode of ossification the capitato-hamatum is variable; in the Frog it ossifies in a diffuse manner, similarly to the unsegmented pollex ; in some Cystignathidce ossification proceeds from one definite centre. In Rhombophryne (fig. 32) a still further fusion had taken place in both fore feet of the solitary specimen which we examined. This consisted, as will be seen, of a coalescence of all the central and distal elements, the two proximal ones alone remaining free. It will be shown in the sequel (p. 172) that we have observed in Phryniscus an unexpected range of individual variation in the fusion of adjacent elements, and we accordingly refrain from proposing a distinctive mane for this bone in Rhombophryne, one individual only having been at our disposal. Postaxiale.-We propose to institute this term for an anomalous compound observed only in Pipa (fig. 1, pk). Its ascending process and all detailed relationships show that it can only be the product of a fusion between the postaxial centrale and the ulnare. With respect to this fusion Pipa stands alone among all known Anura whose feet we have examined1. The lunatum (? radiale) (I.) has undergone reduction consequent upon it, but we do not know sufficient of the habits of the animal to hazard a guess as to its functional significance. III. SPECIAL PART. A. AGLOSSA. a. PIPID^E. Examined :- Pipa americana : large 3 ; feet of a second adult; a young specimen 19 mm. from mouth to vent. Fore Foot (Plate VII. figs. 1 & 2). The radius and ulna are flat with knife-like edges, and the disposition of these bones is exceptional, in that, unlike what is seen in nearly all other Anura, the outer edge of the ulna is directed dorsally. As the result of this, the radius comes to lie in the plane of the extended hand, while the ulna lies above it. The limb-skeleton of this genus was first described and figured by Breyer (9). Later C. Mayer, who confirmed Breyer's observations, working (28, p. 533) with wet specimens, offered certain criticisms upon the observations of Meckel (29) and showed (p. 532), with perfect accuracy, that there are six elements in the carpus. The later researches of A. J. C. Mayer and others have added but little to his description. Carpalia 3 and 4 are perfectly distinct, and it is impossible to examine these and other elements without being struck 1 Born figures (6, pi. 1. fig. 5) a similar but incomplete fusion in the larva of Alytes. This we have never observed. |
