218 JOURNAL OF COMPARATIVE NEUROLOGY. 
Hence, every cutaneous nerve fiber in the dorsal roots 
L. I—Coc. I innervates, on the average, 2.45 mm”. of the 
dermal surface of the leg. 
ES) Drunk: 
Area of surface, one side, 294,160 mm?. 
Number of cutaneous fibers in the dorsal roots of Th. 
II-XII (79-22% of 117,626) 93,182 
294, 160+-93,183= 3.15 mm?. 
Hence, every cutaneous nerve fiber in the dorsal roots 
Th. II-XII innervates, on the average, 3.15 mm”. of the 
dermal surface of the trunk. 
For the purpose of comparison these results may be sum- 
marized as follows: 
Average area of dermal surface innervated by one afferent fiber. 
Body as a whole, 2.05 mm?. 
Head and Neck, 1.08 ‘<< 
Arm, eROnee: 
Leg, Pegs, 0 
Trunk, SUG es 
4. Comparison and Discussion. As already shown, 
DoNALDSON’s estimate of the innervation of the skin is, on 
the average, one cutaneous fiber to every 6.3 mm”. of the 
surface of the skin. Since this estimate is based on Stit- 
LING’s determination of the number of nerve fibers in the 
dorsal spinal roots, it is evident that the source of the differ- 
ence between this estimate on innervation and my own is 
the fact that STILLING’s results are only 40% of mine. To 
show that DoNALDsON anticipated that STILLING’s results would 
prove less than they should be, I quote his statement concern- 
ing them: ‘‘It seems probable that both these estimates (i. e., 
for the fibers in the dorsal and ventral roots) were too low” 
(DoNALDSON 1901). 
The difference between VoISCHVILLO’s results and my own 
is due chiefly to the fact that he used 130,084 mm’. and 
303,566 mm’. respectively for the area of the dermal surface 
of arm and leg, while I used for the same 199,860 mm’. and 
501,680 mm’. In other words, using equal values for the area 
