210 JoURNAL OF COMPARATIVE NEUROLOGY. 
practicable owing to the accumulating evidence that STILLING’s 
estimate of the number of nerve fibers in the ventral roots of 
the spinal nerves, which was used in calculating the number of 
cutaneous fibers in the dorsal roots, was not sufficiently accu- 
rate for our purpose. The data necessary for this calculation 
are the enumerations of the nerve fibers in both the dorsal and 
the ventral roots. The former the author has published (1903), 
as already mentioned. It was therefore necessary to make a 
similar enumeration of the fibers in the ventral roots. This 
being now completed, the estimation of the density of the 
cutaneous innervation in man is possible and is here pre- 
sented. 
II. THE RELATION OF THE CUTANEOUS AND THE MUSCULAR 
NERVE FIBERS OF THE DorsSAL ROOTS OF THE SPINAL 
NERVES oF Man. 
Having determined the number of nerve fibers in the dor- 
sal roots of the left side in man (INGBERT, 1903), our next step 
is to inquire how many of these afferent fibers innervate mus- 
cles and other deep tissues, and how many the skin. 
According to SHERRINGTON’s (1894-95) observations on the 
cat, the afferent nerve fibers ina muscular nerve constitute two- 
fifths and the efferent three-fifths of its fibers. Or in other 
words, in a muscular nerve the afferent nerve fibers are to the 
efferent as 2 to 3. If we assume that this relation is typical of 
all muscular nerves, and if we assume that the same relation is 
true for man, then to the total number of efferent muscular 
nerve fibers, i. e., to the total number of nerve fibers in the 
ventral roots, there must be added two-thirds as many afferent 
fibers in order to make up the muscular nerves. In this calcu- 
lation we have neglected the recurrent nerve fibers in the ven- 
tral roots because, even if present in man, their number must 
be very small. The fibers of the ventral roots passing into the 
white ram communicantes have also been neglected, because 
their number is not great and because we may assume without 
any serious error that the relation between the afferent and 
