432 S. W. RANSON AND P. R. BILLINGSLEY 
In studying the white rami we have found reason for believing 
that the large and medium-sized fibers of the sympathetic system 
are afferent. There are also small myelinated afferent fibers, 
but these are not readily distinguished from the preganglionic 
efferent fibers. It will be evident from what has been said 
that the large and medium-sized myelinated afferent fibers are 
present in varying numbers in different parts of the thoracic 
sympathetic trunk. Between the stellate ganglion and the 
sixth thoracic ganglion they are few in number. Caudal to the 
sixth ganglion there is a steady increase in these fibers with the 
accession of each successive white ramus until the point of origin 
of the greater splanchnic nerve is reached through which nerve 
a large part of these fibers run toward the viscera (fig. 4 B). 
We shall now see that unmyelinated afferent fibers from the white 
rami are distributed in the same way as these myelinated sensory 
fibers which we have been studying. 
Above the level of the fourth thoracic ganglion there are very 
few unmyelinated fibers in the trunk except for the well-defined 
bundle which we have referred to as the crescent. The fine 
myelinated fibers of which the rest of the cross-section is com- 
posed are almost free from an admixture of unmyelinated fibers. 
These are also not very numerous in the oval of the seventh 
internodal segment. In the lower thoracic segments the oval 
well myelinated portion of the section does not consist entirely 
of myelinated fibers, but, as is shown in figure 8, it contains also 
very large numbers of unmyelinated axons. These are grouped 
in small bundles which lie among the myelinated fibers. The 
distribution of the three kinds of fibers, large myelinated, small 
myelinated, and unmyelinated, is not uniform throughout the 
cross-section. The large myelinated fibers are much more nu- 
merous in some parts of the field than in others (fig. 5). They also 
show a tendency to be arranged in bundles which are separated 
from each other by the small myelinated fibers. Now it is in 
and about these bundles of large myelinated fibers that the 
greatest number of the unmyelinated axons are found. The 
grouping of these with the large myelinated sensory fibers sug- 
gests that they also may be afferent in function. The data thus 
