Variation* in Spinal Nerves of Hyla aurea. 273 



While in Bufo variabilis^ nerve XII. only occurs in one per cent, 

 of all cases, in Hyla mora, it was noted in 3-2 per cent. Nerve 

 XI., which was found to be absent in 4"5 per cent, cases in Bufo 

 variabilis, was never absent in Hyla aurea, and while in the 

 latter, the smallest thickness (1) is very rare (1-6 per cent.), the 

 next thickness being the most common, in Bufo variabilis the 

 smallest is the most frequent (36 - 5 per cent). 



In Hvla aurea, nerve X. has a much wider range of thickness 

 than in Bufo variabilis, and while in the latter the greatest 

 number of cases, have the greatest thickness noted for that nerve 

 (9), in Hyla aurea we find that the greatest number of cases 

 have thickness 8, which is in the centre of the range for that 

 nerve (3 to 12), the number of cases in which other thicknesses 

 are found gradually increasing up to 27 "2 per cent, cases for 

 thickness 8, and then gradually decreasing again. A similar 

 difference is seen when we compare the percentages for nerve 

 IX. In Bufo variabilis we again find the greatest thickness 9, 

 in the greatest number of cases (54 per cent.), the percentage 

 occurrence increasing with the increasing thickness up to that 

 point, while in Hyla aurea we see that the percentage increases 

 with an increase in thickness up to 9 in the centre of the range 

 for this nerve, and then diminishes with a further increase in 

 thickness. In nerve VIII. there is no marked difference. In 

 Bufo variabilis 97' 9 per cent, of the cases are divided between 

 the three least thicknesses (4 to 6), and in Hyla aurea 88 per 

 cent, are distributed between the three least thicknesses, which, 

 in this case, are 3 to 5. For nerves VII., VI. and V. in Bufo 

 variabilis we have no data for comparison, but in Hyla aurea we 

 find that for each nerve thicknesses 3 and 4 have by far the 

 greatest number of cases, 4 always preponderating in this respect 

 over 3. 



Nerve IV. in Hyla atirea has a much more restricted range 

 than in Bufo variabilis, and while in this form, two-thirds of the 

 cases have the smallest thickness (4), in Hyla aurea thicknesses 

 3 and 4 are found in a total of 88 per cent, of all cases, the 

 smallest thickness (2) being very rare ( - 8 per cent.). 



Nerve III. The differences between the percentages for this 

 nerve in the two species recall those noted in the case of nerves 

 X. and IX. While in Bufo variabilis the greatest number of 



is 



