380 P. R. BILLINGSLEY AND S. W. RANSON 
TABLE 8 
Branches to the internal carotid artery 
oe ne rts poe NUMBER OF Tienes ae DIAMETERS OF MYELINATED FIBERS 
MILLIMETERS MILLIMETER 1.5 to 3.3 3.3 to 4.5 25 plus 
per cent per cent per cen 
iil 0.1173 1346 11466 68 32 ’ 
VI 0.1038 1845 17774 86 14 
VIII 0.1642 2311 14075 68 32 
IX 0.3149 3933 12482 68 32 
x 0.1751 1741 9934 54 45.5 0.5 
nerves, none of these showed the consistently high ratio of the 
internal carotid nerve. All of the fibers were under 4.5u, except 
in one specimen, not included in the table, in which 32 per cent 
of the fibers ranged from 4.5 to 9u in diameter. 
DISCUSSION 
A comparison of the tables which have been given in this 
paper will make it plain that the myelinated fiber content of the 
various branches of the superior cervical ganglion is in no way 
characteristic of the individual nerves. All of these branches 
are characterized by great variation in the absolute and relative 
number of myelinated fibers found in different specimens. It 
is true that the branches to the cervical nerves show consistently 
a relatively low ratio of fibers to area, and the internal carotid 
nerve shows consistently a rather high ratio, but we are not sure 
that even this represents a significant difference. It would 
seem, however, that the relatively small number of myelinated 
fibers in the branches going to the cervical nerves might be 
characteristic of these branches. . 
How are we to interpret the myelinated fibers found in the 
branches of the superior cervical ganglion? Are they pregan- 
glionic or postganglionic efferent fibers or are some afferent? 
Evidence that postganglionic fibers may acquire a myelin sheath 
has been presented in other papers of this series (pp. 321-323 of 
this issue). The myelinated fiber content of the gray rami 
of the other spinal nerves is similar to that of the rami of the 
