THORACIC TRUNCUS SYMPATHICUS 419 
enth thoracic nerves after all the preganglionic fibers had been 
eliminated. Asis shown in the figure on page 444 of the eleventh 
thoracic white ramus, the majority of the fine myelinated fibers 
have degenerated, but a considerable number of all sizes remain. 
In this particular case the small and medium-sized fibers are more 
numerous than the large ones. In some other degenerated 
white rami the large ones are relatively more numerous. On 
the whole, the sensory fibers of the white rami may be said to be 
of all sizes from 1.5 to 8 or 10u, no one size greatly predominating 
over the others. In some rami as in the upper thoracic larger 
fibers up to 134 may be present. 
These sensory myelinated fibers which are found in the white 
rami after section of the corresponding nerve roots proximal 
to the spinal ganglia take their origin from nerve cells in these 
ganglia. In the second paper of this series we have shown that 
there was no reason for assuming that there were sensory cells in 
the sympathetic ganglia which sent their axons into the dorsal 
roots or spinal ganglia (p. 333). Langley has shown that 
Section of the inferior splanchnics, the lower lumbar sympathetic 
chain, or of a white ramus does not as a rule cause degeneration of any 
medullated fibers in the central ends of the nerves. Sometimes a few 
degenerated fibers may be followed for a short distance, but these appear 
to belong to small gray bundles and to pass off to peripheral tissues. 
When we come to the study of the sympathetic trunk we shall 
find that while some of the fibers of a white ramus end in the 
nearest ganglion, a larger proportion of the fibers run up or down 
in the trunk for longer or shorter distances. That is to say, a 
white ramus is in no special sense associated with its own seg- 
mental ganglion. The gray rami, on the other hand, are in a 
_ very special sense the branches of the corresponding ganglia. 
Gray rami communicantes. The physiological experiments of 
Langley (91 a, 794) on pilomotor, vasomotor, and secretory 
fibers show that the majority of these postganglionic fibers take 
origin from the cells of that ganglion to which the gray ramus is 
attached, but in some cases a minority of the fibers are con- 
nected with cells in an immediately adjoining ganglion. On 
the histological side this arrangement is indicated by the fact 
