SPINAL NERVES OF THE FROG. 121 



an incomplete fusion of the last two vertebrae (8 and 9), 

 so resembling my vertebrae 8 and 9 as to strongly 

 suggest that the two latter are morphologically the eighth 

 and ninth vertebrae of the animal. Compare also Lloyd 

 Morgan, No. 17, and Howes, Nos. 14 and 15. Parallels 

 in Palceobatrachus and other Amphibia are to be found in 

 the works of Boulenger, Camerano, Walterstorff, and 

 Adolphi. 



5. The urostyle is precluded from having taken any 

 part in the abnormality of the vertebral column by the 

 fact that its relative length is normal, and the last two 

 nerves are related to it precisely as in Graupp's scheme of 

 the normal ' k spinal nerves." 



Finally, the explanation above is the most simple, and 

 involves less theory than any other hypothesis. 



The most important works bearing directly on varia- 

 tions in the spinal nerves of frogs and toads are those by 

 Adolphi, Miss Sweet, and Braun. With regard to the two 

 former, I may be allowed to express some dissent from 

 the method of their statistical investigations. These are 

 based practically on variations in the size (" Dicke," 

 " Thickness ") of the nerves forming the plexuses. Now, 

 if the size of a nerve had any individuality, that is to say, 

 if it were any criterion of, or index to, the size and 

 number of its fibres, the method would be beyond cavil. 

 But Ave know from recent work that the size of a nerve 

 is often not constant, nor can it, without investigation, be 

 taken as indicating the true bulk of the nerve, i.e., the 

 number and size of its fibres. It is conceivable that the 

 frog may be exceptional in this, but the conclusions of 

 Adolphi and Miss Sweet can, it seems to me, only be 

 accepted with reservation until their methods have been 

 tested. The former regards both the brachial and lumbo- 

 sacral plexuses to be moving forward, whilst the latter 



