1888.] THE CARPUS AND TARSUS OF THE ANURA. 161 



that of this genus only in that it holds the heads of metacp. 4 and 

 5 in apposition. 



In its mode of ossification the capitato-hamatum is variable ; in 

 the Frog it ossifies in a difi^use 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 terra for an anomalous 

 compound observed only in Pipa (fig. 1, pk). Its ascending pro- 

 cess 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 examined ^ The lunatum (?radiale) (/.) 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^. 

 Examined : — 



Pipa americana : large ^ ; feet of a second adult ; a young 

 specimen 1 9 mm. from mouth to vent. 



Fore Foot (Plate VII. figs. 1 & 2). 



The radius and ulna are flat with knife-like edges, and the dis- 

 position 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 ex- 

 tended 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 



^ Born figures (6, pi. 1. fig. 5) a similar but incomplete fusion in the larva 

 of Alytes. This we have never observed. 



