542 MR. D. W. DEVANESEN ON THE 



appeal" that till now this has been generally regarded as a 

 cutaneous structure, rendered hard and horny in consequence 

 of the nature of its function which is the scooping-out of the 

 soil in suitable localities. This Indian toad has two such con- 

 spicuous tubei'cles, called by Boulenger (2) the "inner metatarsal 

 tubercle "and the "outer metatarsal tubercle." On maceration, 

 it was found that not only these were not purely cutaneous 

 developments, but also that they had their counterparts in liana. 



It is a well-known fact that the Anura possess, in addition 

 to the five toes normally present, an extra vestigial digit — the 

 prehallux. Among the Indian frogs I examined, this digit con- 

 sisted of four cartilaginous pieces in liana hexadactyla, of two 

 pieces in Rana tigrina, and of a single piece in liana hreviceps 

 and Cacopus systoma. The first-mentioned frog is entirely aquatic 

 in habit, and its prehallux forms a slight projection covered with 

 ordinary skin, while in the three last-mentioned ones, which are 

 burrowing forms, the same prehallux is converted into a con- 

 spicuous shovel-shaped organ enclosed in a hard and horny dermal 

 sheath (text-figs. 11 A & 12 A, B, and C). The so-called " inner 

 metatarsal tubercle '"' of C systoma is therefore none other than 

 the distal piece of the vestigial toe of Rana which has acquired 

 a large size and a shape suitable for its function in this toad. 

 That this is so was confirmed by an examination of its connection 

 with a muscle, viz. the abductor hallucis, which is inserted on to 

 the prehallux — a muscular relation identical with what obtains 

 in Rana (Ecker, p. 109). 



In the two terrestrial species of Rana just mentioned, one 

 finds a gradual reduction in the number of pieces constituting 

 the prehallux, assuming the condition in R. hexadactyla to be 

 the normal one. Simultaneously with this reduction, it would 

 appear that in these forms there has been an increase in the size 

 and a change in the shape of the distal piece of the prehallux. 

 This reduction, however, may be regarded as advantageous, for 

 the fewer the number of joints in an organ employed for digging, 

 the greater will be its efiiciency. Thus Ave find in C. systona a 

 single large piece constituting the prehallux*. 



It may be required why I homologise the single element of 

 the prehallux of Cacojjus with the distal piece and not with the 

 proximal one in that of Rana. As the latter piece is in contact 

 with the OS naviculare, just as that of the prehallux of Cacopus 

 is, one may be inclined to the alternative opinion mentioned. 

 But a careful reference to the text-fig. 12 A, B, and C will show 

 that my view is the more probable one ; for it will be seen that 

 while in Rana tigrina the distal piece numbered 4 undoubtedly 

 corresponds to the same piece 4 either in Rana hreviceps or in 

 CacojnLS systoma^ in the latter two species the proximal piece 1 

 of the former has disappeared. According to the alternative 

 vieAV, one will have to say that the distal piece 4 of Rana tigrina 



* I venture to suggest that the so-called spade of the "Spade-footed Toad" or 

 Telohates of Europe is also the preliallux modified. 



