148 ELIZABETH HOPKINS DUNN 
forty days. ‘The variation in size is too obvious to need further 
comment. EH shows the decrease in size among the old rats. 
The increase in size is apparent among the majority of the fibers 
and may include all the fibers. Nevertheless some of the medul- 
lated nerve fibers may appear early and not continue their growth 
over the usual time or may grow more slowly. Small fibers may 
be destined to be small fibers from their first appearance. 
Boughton (’06) made an attempt to classify the medullated 
fibers of the oculomotor nerve into ‘large’ fibers and ‘small’ 
fibers. One is somewhat puzzed regarding his method. Accord- 
ing to his table 1, Boughton entered all the fibers present at eleven 
days as ‘large’ fibers, noting the addition of ‘small’ fibers at later 
ages. In his discussion of method (p. 156) he states that all his 
sections were photographed at the same magnification and only 
those fibers distinctly recognizable at that magnification were 
entered as ‘large’ fibers. If the material was at all comparable 
to that of the present investigation a magnification which would 
show all the fibers at the youngest period would show all the fibers 
at all the other periods. Our fig. 3 proves this. 
The oculomotor nerve carries a considerable number of small 
medullated nerve fibers as viscero-motor fibers to the ciliary 
ganglion (Apolant, ’96, p. 664). The presence of such fibers 
may account for the large number of small fibers found by Bough- 
ton (’06) in the oculomotor nerve of the albino rat. In such a 
group of nerve fibers, which plainly differs functionally from the 
somatic fibers, a distinct difference in size would be difficult to 
interpret alone from the standpoint of age of the fibers. All 
viscero-motor medullated nerve fibers have been recognized as 
small fibers. This was early stated by Gaskell (’86) and Langley 
(96) and corroborated by mahy more recent investigators. It 
is possible that these fibers are later in medullation than those 
passing to the body muscles, but they may not grow so rapidly 
as do the somatic motor fibers. 
Further, if we have in the third nerve which has been considered 
a purely motor nerve, a mixed nerve as Tozer and Sherrington 
(10) have argued, the interpretation of Boughton’s findings has 
an added complication as both efferent and afferent fibers would 
