Donatpson, Law of Innervation. 233 
by these two methods are identical. It would follow from 
this that the first method was probably accurate. On account 
of its shape the foot cannot be tested by this latter method. 
When the area of skin for the thigh is reduced by the 
amount which is not innervated by fibers entering the leg in 
the sciatic and crural nerves, the following percentages are 
obtained as a general average from the three frogs measured : 
TABLE IX. 
Area of Skin. 
Thigh 35.9% 
Shank 25.7% 
Foot 38.4% 
The above percentages are those used in the calculations 
which follow. 
(4). The number of medullated nerve fibers entering the leg 
and also the number distributed to cach segment. 
Having thus determined the proportion in which the ven- 
tral root fibers and the dorsal root fibers entering the leg should 
be distributed to the several segments, it becomes desirable to 
estimate by means of the preceding tables, the total number of 
fibers going to each segment. 
To show how this is done, let us assume that 100 ventral 
root fibers and 176 dorsal root fibers enter the leg—these num- 
bers are in the proportion which has been determined. Then 
63.9% of the 100 ventral root fibers go to the thigh and 35.9% 
of the 176 dorsal root fibers also go to the thigh. Now, in 
order to determine what percentage of the total 276, the sum 
of these two numbers is, we should divide their sum, namely, 
63.9 fibers+63.2 fibers = 127 fibers by the total number of 
entering fibers, namely, 276. We then find that 46% of all 
the entering fibers go to the thigh when they are distributed in 
the above manner. 
Extending the calculation in the same way to the shank 
and foot, we may tabulate the results as follows: 
