STRUCTURE OF THE CRANIAL NERVES 543 



axons at the periphery which passed into the ciUary ganglion. 

 He found a ccmmunicating branch extending from the ophthal- 

 mic division of the trigem'nal nerve to the ciliary nerve, but 

 none to the undivided oculomotor nerve. He did not speak of 

 a direct communication between the nerves studied and the 

 s>in pathetic system, but referred to Jegorow's suggestion that 

 a distribution of abducent fibers to the eyeball in birds might 

 be accounted for by sympathetic fibers joining the abducens as 

 it passed through the cavernous sinus. 



Boughton ('06) found an almost regular increase in the number 

 and size of myehnated fibers in the oculomotor nerve of the 

 white rat and the cat at different ages. In rats of 730 days 

 weighing 414 grams the large fibers averaged 8 1 micni in diame- 

 ter, the small 4.3 micra. In cats of 2893 grams the large fibers 

 averaged 13.5 micra in diameter, the small 7.2 micra. 



Kopsch ('07) described the oculomotor nerve in m;>n as com- 

 posed of about 15,000 mostly large myeliiuited fibers grou])e(l in 

 a number of sccondaiy bundles. In the roots between the fibers 

 were isolated, branched, s])herical nerve cells. The trochlear 

 nerve he described as ccmposed of about 1200 myelinated fibers, 

 the abducens of about 2600 myeUnated fibers. All three nerves 

 received ccn.niunicating branches from the carotid ])lexus of the 

 sympathetic system, and from the ophthahnic nerve. 



THE OCULOMOTOR, THOUIILIvVlJ AND AHOUCIIX T XI:RVIvS 



Specimens of the oculomotor nerve of the dog and of three 

 human adults were studied in serial sections. Upon dissection 

 at least two fine branches from the sym])athetic system could 

 be seen joining the nerve. ^Microscopically sections showed in 

 each case clear pictures of a tj^oical motor nerve (fig. 1) com- 

 posed of large and small mj'eUna ed axons. In the human the 

 ratio of large to small axons was about three to one; in the dog 

 it varied between two to one and three to one. In osmic acid 

 preparations the large myelinated fibers of the dog averaged 12 

 to 16 micra, the small 3 to 6 micra. Close to its peripheral origin 

 the fibei's of the nerve were grouped in one large bundle, with 

 incomplete septa extending toward the center of the nerve. As 



THE JOUKXAL OK COMPAKATIVE NEUROLOGY, VOL. 26. NO. 5 



