THE CERVICAL SYMPATHETIC TRUNK 323 
The myelinated fibers in such a ganglion are extremely few at the 
caudal pole, but increase gradually toward the cephalic end of the 
ganglion. They are scattered uniformly through the cross-sec- 
tion of the ganglion, until they begin to assemble at the upper 
pole to enter the internal carotid nerve. The few myelinated 
fibers that can be seen in the various side branches of the ganglion 
(to the cervical and cranial nerves) are at once lost in the ganglion. 
There are no bundles of medullated fibers running through the 
ganglion from one branch to the other. We believe that all or at 
least most of the myelinated fibers in the branches of the superior 
cervical ganglion arise from cells located in that ganglion. This 
will receive additional support from more detailed study of the 
structure of the superior cervical ganglion to follow. 
Langley (96) has shown that after section of the branches 
peripherally of the superior cervical ganglion nearly all of the 
myelinated fibers which remain connected with the ganglion are 
normal, while nearly all of those separated from the ganglion 
have degenerated, showing that the cells of origin of the great 
majority of these fibers are located in that ganglion. These 
observations were made on the cat. In the dog he has traced 
two small bundles of fibers from the tympanic plexus by way of 
the internal carotid artery to the superior cervical ganglion. 
It is therefore evident that a considerable number of the 
axons arising in the superior cervical ganglion acquire a myelin 
sheath. This is in keeping with the results of v. Kolliker (’94), 
Dogiel (95), Langley (96), Michailow (’11), and others. It is 
interesting to note, however, that Cajal (’11) is of the opinion that 
the axons of the cells of the sympathetic ganglia never acquire 
myelin sheaths. It is easy to understand how he may never have 
been able to trace such an axon into a myelinated fiber, but as 
we have seen this is not the only line of evidence that can be 
brought to bear on the problem. All things taken into considera- 
-tion, the evidence is conclusive that postganglionic axons not 
uncommonly acquire myelin sheaths. 
