250 JOURNAL OF COMPARATIVE NEUROLOGY. 
TABLE XXIV. 
Estimation (DONALDSON) 
Corrected for the Observed 
Splitting fibers (Dunn) Difference Percent. 
Frog B 
Thigh r. 2577 2623 — 46 —1.7% 
Thigh 1. 2608 2600 + 8 +0.3% 
Frog C 
Thigh r. 2884 2814 + 70 +2.5 
Thigh I. 2887 2777 +110 +4.0 
If we take the differences between the estimated and ob- 
served number of fibers to the thigh in all three frogs, B, C and 
B II, we find that the total is 251 fibers, neglecting signs, or 
deducting the — fibers from the + fibers, an excess of + 189 
fibers. In the first case the difference amounts to an average 
of 1.4%, neglecting signs, or +1.1% when the signs are taken 
into account. 
This is a very satisfactory approximation of the estimate 
to the observed number. 
In the case of the shank we have only the two observa- 
tions on Frog B II, with which to make the test. Here the 
approximation is. closer, being 16 fibers when the signs are neg- 
lected, or a difference of — 12 fibers regarding the signs. This 
gives the percentage values of .37% and—.28%. In the case 
of the foot, owing to the fact that we have not the data for con- 
trolling the splitting fibers, the divisions of which have a simi- 
lar distribution, but credit the differences between the estimated 
and observed numbers to this class, the test of the approxima- 
tion cannot be made, as it has been for the thigh and shank. 
However it will be well to point out the reasons in detail for 
thinking that in the nerves to the foot, this class of fibers will 
account for the differences which have been found. 
In the first place, Dr. DuNN (1902, p. 315, Table XII) has 
shown in Frog B II, between S:, just below the branches to the 
thigh and T and P just at the entrance of the trunk into the 
shank, an interval from which no branches are given off—, that 
at the lowest level on the right side there was a gain of 210 
fibers and on the left, 184, or 5.3% on the right and 4.5% on 
the left, the percentage in each case being based on the number 
