98 SYDNEY E. JOHNSON 
In the first sacral internodal segment twenty-nine medullated 
fibers were counted. ‘The proportion of the various sizes was 
practically the same as given above. A few are scattered over 
the entire field, but the majority occur in small groups at or 
near the periphery of the section. 
In the gray ramus associated with the second sacral ganglion 
twenty-five medullated fibers were counted. These are of 
various sizes from about 1.5 up to 9 or more micra. A cross- 
section of the second sacral ganglion contained fifty medullated 
fibers. Most of the fibers are located near the periphery of the 
ganglion, but a good many of less than 4.54 in diameter are 
scattered over the entire section. 
Fifty or more fibers were counted in the second internodal 
segment. Classified as to size, there were two fibers 9u in diam- 
eter, ten fibers 8u, fifteen fibers 64, and the rest ranged from 1.5 
to 5y. All except a few small fibers occupied a crescent-shaped 
bundle in one side of the trunk. 
Caudally in the trunk the medullated fibers decrease slowly 
in number to the third coccygeal internodal segment (as far 
caudad as sections were cut) where the number of large medul- 
lated fibers varied in different specimens from three to twenty 
with a somewhat greater number of smaller medullated fibers. 
Throughout the trunk the largest of the medullated fibers are 
seen at the periphery of the ganglia and internodal segments and 
the majority can be traced into the rami. The smallest of the 
medullated fibers, many less than 1.5u, do not appear to have a 
definite arrangement in the ganglia, but as they enter the inter- 
nodes most of them join the fascicles of larger fibers and enter 
the rami. It seems probable that these small fibers are post- 
ganglionic axones which have acquired thin medullary sheaths. 
The large and intermediate fibers remain to be accounted for. 
Their size and heavy myelinization would appear to preclude 
the possibility of these fibers being either the axones of intrinsic 
commissural neurons or the axones of postganglionic nerve cells. 
Many of the fibers cannot be readily distinguished micro- 
scopically from the axones of preganglionic efferent neurons, but 
the only pathway for anterior root fibers was interrupted by 
