1888.] THE CARPUS AND TARSUS OF THE ANURA. 171 



the radius (fig. 25). The pollex consists of two short segments, 

 borne upon an equally insignificant carpal {po. i.-iii.), the whole 

 standing out at a right angle to the long axis of the fore foot. In 

 the male the head of the second metacarpal is, as Mayer has shown 

 (27), immensely enlarged for support of the horny clasper (** fig. 25). 



It would appear, at first sight, that the displacement of the navi- 

 culare might have been the direct outcome of this enlargement ; but 

 if so, the reduction of the 2nd carpal to the condition of an abso- 

 lutely insignificant nodule (2) becomes unintelligible, for it certainly 

 would appear that that must have resulted from the same cause. We 

 find, in the young specimen at our disposal, that this is really the 

 case, for in the absence of the clasper the 2nd metacarpal is relatively 

 larger. It is interesting to note further, that while, in this specimen, 

 the naviculare does not quite reach the radius, the pollex is propor- 

 tionately much stouter than in the adult. On consideration of these 

 facts we incline to the beUef that the displacement of the naviculare 

 was originally associated with the enlargement of the pollex, in a 

 manner similar to what is seen in Felodytes (fig. II), and that with 

 the reduction of the pollex its connection with the radius became 

 lost, only to be resumed again on the great enlargement of the 2nd 

 metacarpal. 



In the male of Limnodynastes the preaxial border of the second 

 metacarpal bears an irregular bony crest, like that of the Common 

 Frog. We find, however, that the pollex never here fuses with tliis, 

 as it may do in the last-named genus. 



Hind Foot (figs. 24, 27, and 29). 



The typical condition of the Cystignathid hind foot is exemplified 

 in Cystignathus and Limnodynastes (fig. 29), and, as the figure 

 shows, it is, in general. Frog-like—/, e. tarsaJia 2 and 3 are fused 

 to form a single cuboideum (' '). In Leptodactylus this splint is 

 shortened up, so that the hallux-tarsal nearly equals it in size. 



In Ceratophrys the hallux-tarsal is absent, having either fused 

 with the naviculare or disappeared, as believed by Born (3, p. 441) 

 for Rana. 



The calcar is, like the pollex, subject to no inconsiderable variation, 

 as might indeed be expected of a family whose members lead such 

 diverse modes of life. In Ceratophrys (fig. 24), Cystignathus, and 

 Limnodynastes (fig. 29), we have only been able to recognize two 

 segments, the basal one of which represents the tarsal (/>A. i.), while 

 in Leptodactylus the full complement of four pieces is reached. 



Pseiidis (fig. 27) bridges over the interval between these two 

 conditions, in that a small first phalanx is present {p.h. iii.). In 

 this animal the middle or metatarsal segment greatly exceeds the 

 basal one in length, and its proximal outer border is enlaro-ed ; in 

 Limnodynastes this enlargement becomes more obvious, leading up to 

 the condition seen in Ceratophrys ornata (fig. 24), where it assumes 

 the form of a retral spui-i. 



1 This is very feeble in a smaller specimen of C. americana examined. 



