368 P. R. BILLINGSLEY AND S. W. RANSON 
diverse branches of the superior cervical ganglion offer an unusual 
opportunity for determining whether or not myelination is 
characteristic of any particular functional group of these fibers. 
A study of these nerves in several cats also furnishes data as to 
how constant the degree of myelination is in any particular nerve. 
Since the cat is largely used for experimental work on this part 
of the nervous system, it seems desirable to have more accurate 
data than has as yet been published concerning the gross anatomy 
and topography of these branches in that animal. 
In a considerable number of cats the nerves in question were 
dissected out, their topographical relations noted, and a stretch 
of each fixed in osmic acid. The cats were anesthetized and bled 
by cutting the abdominal aorta, to render the field of dissection 
free of blood. ‘The dissection was done with the aid of binocular 
lenses of X2 magnification. Without such magnification many 
of the smallest branches would undoubtedly have been overlooked. 
Dissection was further aided by fine threads tied to the vagus, 
sympathetic, and other nerve trunks, and to the carotid arteries. 
By attaching the threads to iron standards these structures 
could be pulled apart at any desired angle and the exposure of 
the minute branches of the ganglion rendered more easy. The 
field was kept moistened with normal salt solution throughout. 
Sections of each nerve were studied and an enumeration made of 
its myelinated fibers. It was also determined what proportion 
of the fibers fell into each of three dimensional groups. In the 
case of the branches to the superior thyroid artery and the 
cervical nerves the fibers were grouped into the three following 
sizes: 1.5 to 3.3u, 3.3 to 6.6u, 6.64 +. In the other nerves 
another grouping was used, namely, 1.5 to 3.3y, 3.3 to 4.5y, 
4.5u +. Where the number of fibers was not large the fibers 
falling into each group were counted separately with the aid of an ~ 
ocular micrometer. Where the number was large, as in the 
internal carotid nerve, all the myelinated fibers were counted 
together with the aid of an ocular ruled in squares. Then the 
micrometer eye-piece was placed in the microscope and the 
fibers which lay under the micrometer lines were counted sepa- 
rately according to size. The field was then shifted and the 
