430 S. W. RANSON AND P. R. BILLINGSLEY 
branches of the truncus, and since being sensory fibers, it is not 
likely that they terminate in the ganglia, the simplest expla- 
nation of these numerical results would be that through branch- 
ing about half of them became reduced in size below a diameter 
of 6u. 
In serial sections of the sympathetic trunk with the white 
rami attached it is easy to trace the course of the myelinated 
fibers from the latter. In one cat longitudinal serial sections of 
the trunk at the level of the entrance of the sixth white ramus 
were prepared from osmic acid material, also similar sections of 
the trunk at the level of the seventh white ramus. These rami 
joined the trunk at the level of the lower end of the corresponding 
ganglia and could be seen to divide into two bundles, a smaller 
ascending and a larger descending bundle. The majority of the 
fibers do not plunge directly into the ganglion, but seem to run by 
on its surface. This is especially evident in case of the descending 
bundle which can be followed into the trunk below the ganglion. 
It is very easy to follow the large medullated fibers and to see that 
practically all of these in the sixth and seventh white rami turn 
downward past the ganglion into the internodal segment. 
An instructive set of preparations was obtained from another 
cat in which the seventh thoracic ganglion and the associated 
rami were cut into transverse serial sections. The white ramus 
on reaching the ganglion divided into two parts: the smaller of the 
two joined the myelinated portion of the truncus on the surface 
of the ganglion; the other part turned downward in a well- 
defined fascicle separated from the ganglion by a connective- 
tissue septum and could be traced downard for a considerable 
distance along the side of the seventh thoracic internodal seg- 
ment before it joined with the trunk. So far as could be de- 
termined all the large fibers of this white ramus turned downward 
in this fascicle. Such a separate-descending fascicle is of course 
atypical, but this ramus serves to indicate in a diagrammatic 
way the course taken by the fibers of the white rami on enter- 
ing the trunk. Of course the corresponding fibers of the upper 
thoracic white rami turn upward instead of downward. 
