ANATOMY OF RANA TIGIUNA. 607 



characteristic of these structures in the Ranidae. In some 

 specimens I have observed a flattening even of the distal 

 extremity of the diapophysis, which, too, is sometimes to be 

 noticed in the immature Rana temporaria. The neural spine is 

 somewhat variably developed, but is always represented by at 

 least a slight elevation in the mid-dorsal line. From this a pair 

 of distinct ridges diverge. These pass outwards and backwards 

 onto the dorso-posterior face of the transverse processes, but fade 

 out before I'eaching the distal end. 



The coccyx, too, in R. tigrina differs from that of R. tempo- 

 raria or of R. esculenta in that the paired foramina which, in 

 these European species, permit of the exit of the tenth pair of 

 spinal nerves are very frequently absent from the Indian species. 

 When, however, they do occur, they are generally very minute 

 indeed, and not uncommonly, upon one side or both, this 

 external opening leads only into a blindly ending canal. As an 

 infrequent variation, specimens are seen in which there may be 

 two apertures upon one side. In such cases only the upper 

 canal appears to have open communication with the vertebral 

 canal. Such a condition is figured in my account of the Anuran 

 coccyx ('15, fig. 1 b, X., xi.). 



It is probable that we have here the last vestige of an aperture 

 for the lost eleventh spinal nerve, such as is still found occasionally 

 in the more primitive Anura. 



From the foramen of the tenth nerve, when present, there 

 runs backwards and upwards a slight groove which is often 

 several millimetres in length. 



Of a total of 32 coccyges examined, only four (12^ per cent.) 

 showed a jjair of canals for spinal x., and, of these, the openings 

 in three were very small. In five other specimens a pair of 

 extremely minute external apertures were found, but on neither 

 side of three of these was there a clear passage for the finest 

 hair. The remaining tioo permitted the passage of a very fine 

 hair on one side only. 



In seven other specimens a single aperture only was found, but 

 in only two cases was I able to pass a hair into the vertebral 

 ca.nal. In the remaining five specimens the canal apparently 

 ended blindly internally. 



Thirteen coccyges (40 per cent.), including four specimens in 

 which the vertebral column was abnormal in other ways, showed 

 a complete absence of the foramina on both sides. 



Three specimens exhibited two minute apertures on one side 

 and a single aperture only upon the ©thex'. Of these, in one 

 sjjecimen all the canals ended blindly, and of the remaining two 

 each had a single canal on that side upon which there were two 

 apertures. 



In the twelve asymmetrical cases the canal (or aperture) 

 occurred in eight cases upon the right side and in four upon 

 the left. 



It is a little difficult to decide what is to be regarded as the 

 normal condition of the coccyx in i?. tigrina. It is probably 



42* 



