THE CERVICAL SYMPATHETIC TRUNK 321 
Langley has shown that stimulation of the sympathetic trunk 
in the neck causes no general body reflexes of any kind. It must, 
therefore, be devoid of sensory fibers, at least of those carrying 
painful afferent impulses. We have been able to confirm this 
physiological observation and our histological results are also 
in agreement with it. On page 4382 we will shotv that the char- 
acteristic sensory fibers of the sympathetic trunk are the large 
myelinated and the unmyelinated. Except for two or three large 
myelinated fibers, there are no fibers which would be interpreted 
as sensory ascending in the cervical portion of the sympathetic 
trunk. 
STRUCTURE OF THE NERVUS CAROTICUS INTERNUS 
The chief set of branches given off by the superior cervical 
ganglion ascends from its upper pole to the internal carotid 
artery. Of these one or two are of large size in the cat. These 
large ones are easily and positively recognized in serial sections 
of the ganglion and its branches. The entire group of from three 
to five branches forms the nervus caroticus internus. It con- 
sists of both myelinated and unmyelinated fibers the latter of 
course predominating. Figure 3 shows the relative size, number, 
and arrangement of the myelinated fibers in this nerve in the cat. 
These fibers are rather widely separated by great numbers of 
unmyelinated axons and are of about the same size as those of 
the sympathetic trunk. They vary in diameter from 1.5y to 
4.5u with an occasional larger fiber up to 7u. Their distribution 
is quite uniform throughout the nerve. The thickness of their 
myelin sheath seems to be somewhat less than that of those in 
the sympathetic trunk. 
These myelinated fibers are so numerous that interest is at 
once aroused as to their source, and the possibility suggests 
itself that they are preganglionic or perhaps afferent fibers from 
the trunk which have run through the ganglion without interrup- 
tion. This possibility is easily excluded, however, by section 
of the trunk below the ganglion. After all the myelinated fibers. 
in that trunk have degenerated the structure of the internal 
THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 29, No. 4 
