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Dr. W. H. Gaskell. Structure, Function, [Feb. 23, 



In order to see how far the cranial nerves conform to the same type 

 as the spinal nerves, I will consider their structure and distribution 

 seriatim, leaving out of consideration for the present the olfactory, 

 the optic, and also, for reasons to be mentioned, the auditory nerves. 



Beginning then with the Illrd or oculo-motor nerve, we are dealing 

 with a nerve whose function at the present time is purely motor, a 

 nerve therefore which is ordinarily spoken of as representing an 

 anterior root; in this nerve we find indications of a large-fibred and a 

 small-fibred part. Tracing up these fibres outwards to their destina- 

 tion it is seen that the large fibres pass oif to supply the eye muscles 

 supplied by this nerve, while most of the small fibres separate out 

 from the large fibres and pass directly into the ganglion oculo-motorii. 

 This ganglion, which is in the main formed by these small medullated 

 fibres of the Illrd nerve, i.e., radix brevis, is increased in size by the 

 addition of ganglion cells formed on the radix; longa from the 

 trigeminal, and others in connexion with sympathetic fibres ; the 

 fibres in the ganglion are all of small size, and the short ciliary nerves 

 which arise from it have not a single large fibre among them. The 

 nerve fibres of the short ciliary nerves are almost all medullated, and 

 according to most observers (Bidder and Yolkman) are more 

 numerous than those entering the ganglion, so that in this case these 

 small nerve fibres which are motor to the ciliary and splanchnic muscles 

 do not lose their medullary sheath in their passage through the 

 ganglion, a peculiarity which distinguishes them from the motor 

 nerves of the vascular system, and is suggestive in connexion with the 

 fact that these muscles though unstriped in structure are to a certain 

 extent voluntary in action. 



Also the nerve cells of this ganglion are distinctly of two kinds, 

 most of them unipolar, of the same type as those of a spinal ganglion, 

 the minority multipolar of the type of the so-called sympathetic 

 ganglion cells : this also suggests that this difference in the type of 

 nerve cell is associated with the presence or absence of a medullary 

 sheath in the nerves issuing from the ganglion, and does not 

 necessarily imply that these unipolar cells are connected with 

 posterior root fibres, and that therefore, as has been supposed, this 

 ganglion is the root ganglion of the oculo-motor nerve. 



We see then clearly that the oculo-motor ganglion is the ganglion of 

 these small-fibred efferent nerves of the Illrd nerve. 



The Illrd nerve then conforms in its structure, and in the vagrant 

 character of its motor ganglion, to the plan of a spinal nerve as far as 

 its anterior root is concerned. Where then is its posterior root ? If 

 it conforms to the plan laid down, the ganglion on the posterior root, 

 i.e., its root ganglion, ought to be situated on the nerve near its exit 

 from the central norvous system, and here, in fact, I have found it in 

 the nerves of man and sheep. I have made a series of consecutive 



