INGBERT, Dorsal Roots of Spinal Nerves. a5 
VILL. The Application of the Numerical Results to the Innerva- 
tion of the Skin. 
The author had hoped at this time to publish his estimate 
of the innervation of the dermal surface of the human body 
based on the enumeration here made. In making such an esti- 
mate the number of afferent fibers innervating the skin and the 
muscles respectively was calculated by the aid of results ob- 
tained by Sri_tinGc and VorscuviLto. But since this part of 
the thesis was written the author has commenced an enumera- 
tion of the number of nerve fibers in the ventral roots of the 
spinal nerves of man. This investigation as far as carried out 
shows that the relation of the number of nerve fibers in the 
dorsal, and the ventral roots as given by STILuine is not suffi- 
ciently accurate for an estimate of the innervation of the skin. 
The publication of this part of this investigation will therefore 
be deferred until the number of nerve fibers in the ventral roots 
of the spinal nerves of man has been determined, thus present- 
ing proper data for calculating the percent of the dorsal root 
fibers which innervate the skin and the muscles respectively. 
LX. Summary. 
1. The total area of the cross-sections of the dorsal roots 
of the left spinal nerves of a large man is 54.93 mm.” 
2. The total number of medullated nerve fibers in the 
dorsal roots of the left spinal nerves of the same man is 65 3,- 
627; and the total number on both sides would therefore be 
about 1,307,254. The error in this instance is probably less 
than 2%. ' 
3. There are, on the average, 11,900 medullated nerve 
fibers to every sq. mm. of the cross-sections of the dorsal roots 
of man. 
4. There is a close relation between the area of the cross- 
sections of the dorsal roots and the number of nerve fibers 
which they contain. (See Chart III, Fig. 1.) 
5. The small fascicles of a dorsal spinal root, in general, 
contain nerve fibers of small caliber. 
