ON A SAW. DETERMINING THE NUMBER (OF 
MEDULLATED NERVE FIBERS INNERVATING 
ia iniGh, SHANK AND) POOP OF | THE 
FROG—RANA VIRESCENS. 
By Henry H. Dona.pson. 
(From the Neurological Laboratory of the University of Chicago.) 
During the past three years, while following the studies of 
Dr. Dunn (1900 and 1902) on the innervation of the frog’s leg, 
it has been my endeavor to discover whether there was any law 
determining the distribution of the medullated nerve fibers to 
the segments of the leg. This law has been found and is 
expressed as follows : 
The nerve fibers entering the leg of the frog (Rana virescens) 
by the sciatic and crural nerves, are distributed to the thigh, shank 
and foot in numbers which, for each of these segments are equal 
to the sum of the efferent fibers,—taken in proportion to the weight 
of the muscles,—and of the afferent fibers,—taken in proportion to 
the area of the skin, 
The data discussed in the following pages are intended to 
furnish the evidence for the law just stated. 
To make this investigation it was necessary to know: 
(1) The relative number of medullated ventral and dor- 
sal root fibers in the nerves supplied to the frog’s leg. 
(2) The relative weight of the muscles of the thigh, 
shank and foot. 
(3) The relative areas of the skin for the thigh, shank 
and foot. 
(4) The number of medullated nerve fibers entering the 
leg and also the number distributed to each segment. 
(5) The number of medullated fibérs distributed as mus- 
cular and cutaneous nerves to each segment of the leg. 
