542 SUMNIOIl L. KOCH 



(l;isk(>ll ('S<)) stii(li(Hl the ci'anijil nerves with especial reference 

 to their relation to a ty])ical spinal nerve. The oculomotor, 

 trochlear and abducent nei'A'c^s he described as pure efferent 

 nerves. The oculomotor was composed of large and small mye- 

 linated fibers, in the dog 14.4 to 18 micra and 3 to 5 micra in 

 diameter. The smaller fibers passed to the ciliary ganglion, the 

 larger to the extrinsic muscles of the eye. The trochlear nerve 

 consisted of large myehnated fibers, 14.4 to 18 micra in diameter, 

 supplying the external oblique muscle, and small myelinated 

 fibers 3.6 to 5.4 micra in diameter, of unknown function. The 

 abducens consisted of large myelinated fibers 14.4 to 18 micra 

 in diameter, and a few smaller ones, but contained no distinct 

 group of small fibers as did the Ilird and IVth nerves. In the 

 roots of these nerves he saw fibrillar structures which he inter- 

 preted as the remains of ganglion cells present at an earlier stage 

 of their development, and representing the afferent portion of 

 the nerves. 



Barratt ('98, '99, and '01) described the oculomotor nerve as 

 composed of large and small myelinated fibers, 11 to 15 micra 

 and 3 to 5 micra in diameter, in about the ratio of three to one. 

 He found unmyelinated fibers also, ''both in the fibrous sheath 

 and in the main trunk; in the latter situation usually at the 

 periphery." He did not find any communication with the cav- 

 ernous plexus nor with the ophthalmic division of the trigeminal 

 nerve. The trochlear nerve was composed of large and small 

 myelinated fibers 12 to 19 micra and 4 micra in diameter, in the 

 ratio of three to one. There were no unmyelinated fibers pres- 

 ent. The abducent nerve he described as composed of large 

 and small myelinated fibers, 11 to 17 and 3 to 6 micra in diame- 

 ter. A few small twigs composed of small myehnated and un- 

 myehnated fibers joined it 25 mm. from its superficial origin, and 

 left it again 10 mm. distalward. 



Carpenter ('06) studied the development of the oculomotor 

 and abducent nerves in the chick. He found that the oculo- 

 motor nerve was composed of myelinated axons 3 to 15 micra 

 in diameter. The trunk was composed of comparatively large 

 axons, with a few scattered small axons, and a zone of small 



