Hardesty, Spmal Nerves of the Frog. 



83 



and IXth nerves of the two specimens employed in Tables I 

 and II, and determining the percentage of the excess of the 

 fibers of the dorsal roots indicated by these sums we get 



TABLE IX. 



Rana virescens. 



Wt. of frog. 



48.2 grams. 

 59.52 grams. 



Total number 

 fibers in Dor- 

 sal Roots. 



4737 

 4246 



Total number 

 fibers in Ven- 

 tral Roots. 



2732 

 2421 



Excess of 



Dorsal Root 



fibers. 



2005 

 1825 



Percentage. 



73-7 

 754 



Thus, an increase in the excess of fibers in the dorsal root 

 is found not only for an increase of 40 grams in weight but also 

 for an increase of only 1 1 grams in weight. Also the increase 

 in weight being slight, the increase in the excess of dorsal root 

 fibers is correspondingly slight. So, it is hoped that some evi- 

 dence is added to that brought forth by Birge to the effect that 

 as the animal increases in size, the number of dorsal root fibers 

 increases more rapidly than that of the ventral root. 



It may be fairly asserted that by far the greater part of the 

 sensory or dorsal root fibers of the frog go to innervate the skin. 

 As the animal grows the skin of course increases in area, but 

 exactly what relation this increase in the excess of sensory 

 over motor fibers has to the increase in the area of the skin, is 

 yet to be investigated. 



A very interesting relation is found to exist between the 

 numbers of the dorsal and ventral root fibers present in those 

 nerves which contribute their fibers to the inervation of the leg. 

 It is known that, in the frog, the Vllth, Vlllth and IXth 

 nerves give nearly all their trunk fibers to the formation of the 

 sciatic nerve. If the sums of the dorsal and ventral root fibers 

 of these three nerves be taken and the one divided by the oth- 

 er, there is obtained for each of the above specimens the pro- 

 prortions represented in Table X. 



