566 Dr. G. E. Nicholls. Intracranial Ganglion upon the 



ganglion persists, the ciliary ganglion may prove to be composed, strictly of 

 sympathetic elements. 



Herein, perhaps, lies .an explanation of the contradictory observations 

 which have been recorded, and the diverse opinions expressed in the 

 controversies concerning both the nature of the ciliary ganglion and the 

 segmental value of the oculomotor nerve. 



The fact that ganglion cells are known to occur upon ventral spinal roots, 

 constantly in the cat,* and occasionally in man and monkey, must not be 

 overlooked. These cells are not, however, associated with afferent fibrest 

 nor related to sensorial end-organs. What their nature and function may be 

 has not yet been explained, but they are clearly not comparable with the 

 cells found in the roots of the eye-muscle nerves. Neal ('14, p. 58) remarks, 

 in connection with the migration of medullary cells into the oculomotor and 

 trochlear nerves, that a similar migration is observed in the case of the 

 abducens which has no related sympathetic anlage, and that in this case 

 these cells can have no destination other than the neurilemma. In the 

 specimens which I have examined, ganglion cells were apparently absent 

 from the roots of the fourth and sixth nerves. From the results obtained by 

 Graskell, Sherrington and Tozer, however, it would seem that both of these 

 nerves also are sensori-motor, and have ganglion cells upon their roots in 

 some species. 



In the case of the trochlear nerve, Neal points out that, in development, 

 it is closely associated with fragments of the neural crest and is related 

 to a transient sympathetic ganglion. The abducens undergoes considerable 

 dislocation, and has lost all trace of any relation to a sympathetic ganglion 

 anlage, if such ever existed. Nor has any connection between this nerve 

 and the neural crest been recorded. Nevertheless, it would seem that the 

 arguments adduced in favour of the segmental value of the oculomotor would 

 apply, in the main, to all the eye-muscle nerves, making allowance for the 

 progressively greater reduction and displacement which has occurred in the 

 two more posterior nerves. 



In conclusion, I would submit that the occurrence in the oculomotor of 

 afferent nerve fibres (conducting centripetally impulses arising in sensorial 

 end-organs), and of ganglion cells upon the root of the nerve almost certainly 

 related to these afferent fibres, taken in conjunction with the part which 

 this nerve plays in the development of the ciliary ganglion, constitutes 

 evidence in favour of the complete segmental character of the nerve too 

 important to be ignored. Neal, who upholds a view opposed to this, says 



* Schafer, '80, p. 348. 

 t Sherrington, '94«. 



