BRANCHES OF GANGLION CERVICALE SUPERIUS 369 
process repeated until a total of one hundred fibers was counted. 
From these data the proportion of fibers of the three sizes was 
determined. An oil-immersion objective was used throughout 
in measuring the fibers. 
In order to determine the relative richness in myelinated fibers, 
i.e., the proportion of the myelinated to the unmyelinated, the 
area of the section was determined in each case by projecting its 
outline with the aid of the camera lucida onto millimeter paper 
and determining the number of square millimeters which it cov- 
ered. Knowing the magnification, it was easy to determine 
the actual area of the nerve in cross-section. This is expressed 
in square millimeters in the first column of each table. The 
second column gives the total number of myelinated fibers in the 
nerve, and the third shows the number of myelinated fibers per 
square millimeter. Since none of the nerves had an area as 
large as 1 sq. mm., the figures in the third column are greater than 
those in column 2. Since the greater part of the area is filled 
with unmyelinated fibers, this ratio (myelinated fibers into area) 
gives a rough method of comparing the number of myelinated 
and unmyelinated fibers in the different nerves. Considerable 
error is necessarily introduced into the determination of the 
area of the cross-section of a nerve by two factors, unequal shrink- 
age during fixation and unequal spreading of the sections on the 
slide. But these factors can account for only a small part of the 
actual variation of a given nerve in different cats as shown in the 
tables. Where a nerve was presented by two or more separate 
fascicles their areas were added together and the sum taken as 
the area of the nerve. It is probable that in some cases fascicles 
belonging to a nerve were lost during dissection, and if so, this 
would help to account for a part of the variation in size of the 
nerves in different cats. It may be also that there is some ndi- 
vidual variation in the course taken by the postganglionic fibers 
or in their number. This variation in size is of interest and may 
be of significance, but except in so far as it is due to shrinkage 
or spreading, does not affect the question with which we are here 
primarily concerned, namely, the number of myelinated fibers 
per square millimeter of the cross-section of the nerve. 
THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 29, No. 4 
