102 SYDNEY E. JOHNSON 
connected by two or more strands representing the internodal 
segment. Fusions between opposite ganglia of the same segment - 
are common. By degenerative section of the trunks and dorsal 
roots the internodal segments are reduced to the finest thread- 
like filaments. 
The number of medullated fibers contained in the first sacral 
internodal segment varies a great deal in different specimens. 
The numbers observed ranged from 400 to 700, although counts 
were not made with the greatest possible care and a good many 
of the smallest fibers may have been missed. The fibers are of 
all sizes from about 1.2 to 9 or more micra in diameter. The 
majority of these fibers degenerate when the trunks are divided 
caudad to the lowest white ramus. In view of this fact and other 
evidence previously considered, it seems practically certain that 
the fibers in question are dorsal and ventral root fibers which 
have descended in the trunk from the lower white rami. The 
very large fibers are obviously sensory fibers from the spinal 
ganglia. That a good many of the small and intermediate 
fibers must be from preganglionic efferent neurons is indicated 
by the disappearance of the intercellular plexus in these speci- 
mens. The fibers which remain after the single operation 
described above number approximately from ten to fifty in 
different specimens and are of all sizes seen in the normal trunk. 
Section of the dorsal roots in addition to the first operation 
caused all of these fibers to degenerate, except an insignificant 
number which were thinly medullated and mostly under 1.5u 
in diameter. All fibers which remain after the first operation 
except these few very small ones appear therefore to be dorsal 
root fibers which have reached the trunk by way of the gray 
rami. Langley (’96) admits the possibility of the gray rami 
containing a few dorsal root fibers, but such a relatively large 
number was not anticipated. The small fibers which remain 
after the double operation do not occur constantly in different 
specimens nor regularly in successive internodes of the same 
specimen. Five was the largest number seen in the cross-section 
of any internodal segment. In most instances they could be 
traced into the gray rami. It seems probable that these fibers 
