544 MR. D. W. DEVANESEN ON THE 



In this toad a further specialisation of the digit in question 

 seems to have been brought about in its relation to the tarsus. 

 It is firmly attached to the os naviculare, as has been already 

 described in connection with the latter, and through the inter- 

 vention of the same it articulates exclusively with the astragalus. 

 This articulation, I should think, in combination with the action 

 of the muscles attached to it and to the tarsal bone mentioned, 

 bestows a considerable advantage in the act of burrowing (text- 

 fig. 11 B and C). In R. tigrina and R. breviceps the specialisation 

 has not been carried to that extent ; the same indirect articula- 

 tion of the prehallux with the astragalus is only partial, as the 

 first digit still continues to articulate with the latter indirectly 

 through the os naviculai-e ; further, the prehallux and the tarsal 

 bone connected with it are, in these frogs, much less calcified, 

 and consequently they are less rigid and hard. Again, the 

 plantaris muscle, which has no relation with the prehallux in 

 Rana, has a connection with the same in this toad, in that it is 

 indirectly inserted on to the latter by means of a fascia (text- 



It is exceedingly interesting to find the digit, which is generally 

 believed to be a vanishing structure in the Anura, re-asserting 

 itself under suitable conditions and becoming an organ of no 

 mean importance to its possessor. This specialisation of the 

 prehallux among the species of two diflferent families, viz. the 

 Engystomatidse and the Ranidse, may be regarded as a case of 

 convergence. 



The " outer metatarsal tubercle " of this toad, though smaller 

 than the inner one, consists likewise of a single cartilaginous 

 piece covered with a horny dermal layer. I identify this as 

 the " OS sesamoide " (Ecker, p. 106) of i^cwia, which is a carti- 

 laginous element situated on the plantar side of the joint 

 between the calcaneum and the fourth metatarsal bone. In this 

 latter position exactly I found the cartilage of the " outer meta- 

 tarsal tubercle " situated in C. systoma, so that this also is no 

 new structure developed by this toad, but is only a specialised 

 and an exaggerated one of what is normally present in Rana. 

 Nevertheless, it would seem that a remarkable specialisation had 

 been brought abovit in its alliance with no less an important 

 muscle than the gastrocnemius. To this " os sesamoide " is exclu- 

 sively inserted the narrow, attenuated yet strong band of the 

 aponeurosis 'plantaris. This implies that an important calf muscle 

 is concerned in the working of the "outer metatarsal tubercle" 

 (text-fig. 110). 



7, The Jfusculattcre. 



The muscles of the hyoid apparatus and of the floor of the 

 mouth are characterised by a great specialisation in this toad, 

 a remarkable fact observed also by Beddard (1) in three other 

 membei'S of the same family. However, in the details of the 

 specialisation, excepting perhaps in the sternohyoideus, one does 



