SECOND CERVICAL NERVE OF THE RAT 149 
be included. Such an interpretation has been given to the func- 
tion of the ventral roots by Kidd (11) and others. I have 
unpublished a note on the presence of medullated nerve fibers 
in the ventral roots of the spinal nerves in the leopard frog, which 
from the direction of their degeneration seem to have their cells 
of origin in the dorsal root ganglia. It may be then that in no 
nerve or spinal root are we dealing with unmixed fibers. The 
relative number of efferent fibers seems greater in the second 
cervical nerve than in any of those previously considered. Roth 
(05) states as an argument in proof of the visceral character of the 
eleventh cerebral nerve that in the rat the ventral roots above the 
sixth cervical have a small number of small medullated nerve 
fibers, and that the second cervical nerve has in its rami communi- 
cantes few or no small medullated nerve fibers. 
Willems (11) has discussed the question of the size of medul- 
lated nerve fibers quite fully giving prominence to three theories 
and introducing one of his own based on the differences in size 
found among the branches distributed to various muscles from the 
efferent portion of the fifth cerebral nerve in the rabbit. Quoting 
from page 203, ‘‘ Nous pensons done que l’individualité des nerfs 
a son origine principalement dans la différente valeur de l’accrois- 
sement secondaire pour chaque muscle.”’ 
It has seemed to the writer that the propounders of these so- 
called theories as set forth by Willems have not attempted to put 
forth an all embracing theory, but have each one been attempting 
to define factors which may influence the size of the medullated 
nerve fiber. Each one has noted conditions which have run paral- 
lel with size and have been piling up evidence bit by bit. At the 
present moment it seems most probable that the size of the medul- 
lated nerve fibers must be interpretated finally as due to a com- 
bination of causes, and I anticipate that all the bits of information 
will be wrought into a complex mosaic when the final illuminating 
word can be said. One can readily see that in regard to size the 
neurones may appear in successive crops so that the earlier crop 
may have a greater size, according to Boughton’s and Donald- 
son’s attractive theory, while at the same time these successive 
crops have definite functional values which in turn may be influ- 
