Variation* in Spinal Nerves of Hyla aurea. 279 



thickness 3, occurs chiefly with nerve III., thickness 9, and 

 nerve II., thickness 6, with nerve III., thickness 10. 



Comparing the evidence of these tables with that obtained by 

 Adolphi for Bufo variabilis, we find that on the whole there is a 

 confirmation of Adolphi's results with reference to the sacral 

 plexus. In Table 9, showing the variations in thickness of 

 nerve XI. accompanying those of nerve IX., there is partly a 

 confirmation and partly a denial, similarly in Table 17 for 

 nerves X. and III. Tables 13 (nerves XL and II.) and 18 

 (nerves X. and II.), on the other hand give a somewhat 

 positive result, where in Bufo variabilis we see no connection : 

 while Tables 20 (nerves IX. and IV.), 23 (nerves VIII. and 

 IV.), 25 (nerves VIII. and II.) perhaps, 26 (nerves IV. and 

 III.), and possibly 27 (nerves IV. and II.), offer results directly 

 opposed to those obtained from similar tables for Bujo variabilis: 

 while Table 28 (nerves III. and II.) exactly compares with 

 Adolphi's results for similar nerves. The chief difficulties are 

 with reference to the brachial plexus. Instead of nerve IV., 

 the most posterior of the brachial plexus in Hyla aurea, being 

 in a condition of decrease in thickness as in Bufo variabilis, 

 Tables 20 and 23 distinctly show that it is in a condition of 

 increase, Table 11 being the only one disagreeing with this in 

 the slighest degree. Moreover, if this inference be correct, viz., 

 that nerve IV. is in a state of increase in thickness, then by 

 Table 26, nerve III. also must be increasing in thickness, and 

 this result for nerve III. exactly agrees with Adolphi's observa- 

 tions for Bufo variabilis. Further, Tables 13, 18, 25, and 27, 

 in which a relation is seen between nerve II. and the other 

 nerves, point to the fact that nerve II. is decreasing in 

 thickness, and this also agrees with Bufo variabilis.! Assuming 

 that Adolphi's conclusions based on his examination of the larva 1 

 of Rana temporaria and Pelobates fuscus be correct, that the 

 thicker condition of nerves X., XL, and XII. is the more 

 primitive, if as seems to be the case from the tables in Bufo 

 variabilis, a greater thickness of nerve IV. is found with a 

 greater thickness of nerves XL and X. and pari passu with 

 these, the smaller thicknesses of nerves IX., VIIL, and III., 

 and vice versa, the smaller thicknesses of nerves XL, X. and 



% Adolphi : loc. cil , 1893, p. 341. 



