1888.] THE CARPUS AND TARSUS OF THE ANURA. 163 



at first sight to be sesamoids (they were described as such by Mayer 

 28). The postaxial one lies altogether free of the tarsus, and it is 

 beyond doubt, as Gegenbaur has asserted (18, p. 66), a sesamoid. 

 The lamina of bone deriyative of the middle one has all the relations 

 of a reduced cuboideum of such an animal as the Frog ; and we can 

 only interpret the bone which gives origin to it as that structure, 

 thrust out of position by the great development of the astralagus and 

 calcaneus, probably as an accompaniment of the great elongation of 

 the metatarsals. 



The third or preaxial bone of the above-named series is clearly 

 the naviculare. Firstly, it gives insertion to the tendon of the add. 

 longus digiti I. muscle, which feature we have shown (p. 148) to be 

 characteristic of that element ; secondly, it carries a diminutive 

 calcar of two short but ossified segments. 



The young specimen examined shows no trace of distinct hallux- 

 tarsal, nor have we been able to obtain any clue to its whereabouts. 



b. Dactylethrid^. 



Examined : — 



Xenopus IcBvis : three adults; young tadpole. 

 Xenopus calcaratus : hind half of a late tadpole. 



Fore Foot (Plate VII. fig. 4). 



This carpus presents fewer anomalies than that of Pipa. The 

 ulnare {p) is quite distinct and in no sort of fusion with the post- 

 axial centrale {k). Our fifth carpal is wanting, but those of the 

 four remaining digits are large and distinct. The naviculare (w), is 

 m Its large size and in the possession of a preaxial spur, quite unlike 

 that of Pipa. ^ * 



As in Pipa, the metacarpals are greatly elongated ; this genus is 

 exceptional, however, in the great expansion of the head of the 4th 

 one (4') and the excavation of that of the 5th for the reception of a 

 special peg of the postaxial centrale {k). 



The lenticular sesamoid (indicated in a dotted line) hes, in this 

 genus, in the line of junction between the radius and ulna, instead of 

 being preaxial as in Pipa. 



Hind Foot (Plate VII. fig. 3). 



The astragalus and calcaneus are much more normal than in 

 Pipa, their extremities are very broad (fig. 3), and the distal epiphy- 

 sial cartilage ossifies from three independent centres (see fig. 3). 



There overhes the head of the second metatarsal a smairbone (1) 

 which is wedged in between it and the centrale (naviculare n) ; we 

 regard this as the tarsal of the hallux, for reasons .already given 

 (p. 146) in dealing with the same condition in Bufo and the Tree- 

 Frog. The bone marked " ^ we accordingly hold to represent the 

 fused tarsaha of the 2nd and 3rd digits. 



The metatarsals are much elongated and the head of the third one 

 (3') is exceptional for its great breadth ; seeing that the tarsals are com- 



