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



existence of these cells he put forward the hypothesis that " both third and 

 fourth nerves are in themselves complete segmental nerves of the type which 

 Balfour supposes to have been the original type ' when mixed motor and 

 sensory posterior roots were the only roots present ' ; that then owing to some 

 change which occurred during the past history of the vertebrate the sensory 

 parts of these two nerves degenerated and their place was taken by the 

 sensory elements of the fifth nerve." 



Two other early observers, Keissner and Rosenthal,* are also said to have 

 recorded the existence of cells in the root of the third cranial nerve. Accord- 

 ing to Sherrington, the former suggested that these cells were connected with 

 the sympathetic system. 



Of the occurrence of (presumably) actively functional ganglion cells upon 

 the oculomotor root, in numbers comparable to those which I have found in 

 S. canicula, the only record, so far as I can discover, is contained in the paper 

 by Miss Tozer('12). This author found ganglion cells in (or near) the roots 

 of the third, fourth, and sixth cranial nerves of young Macacus rhesus and of 

 a teleost {Gaelics virens) and in the third and sixth roots of the common 

 pigeon. 



It would appear, then, that oculomotor gangliaf are present, either as 

 functional structures or as vestiges, in widely separated vertebrate classes. 

 Since ganglia, other than sympathetic, are known to occur normally only 

 upon " sensory " nerves, or if upon mixed (motor and sensory) nerves, then 

 upon the dorsal (sensory) root only, a question at once presents itself — What 

 is the significance of the occurrence of ganglia upon the oculomotor root ? 



In seeking an answer to this question it will be necessary to discuss the 

 generally accepted belief in the homology of the oculomotor nerve with a 

 ventral spinal root in the light of our present knowledge of (a) the composition 

 of this nerve and (b) its relation, in development, to the ciliary ganglion. 



The Comparison of the Oculomotor with a Ventral Spinal Nerve Boot. 



That the oculomotor has, of recent years, been accepted by the great 

 majority of authors as a purely motor nerve, composed only of somatic motor 

 components and equivalent simply to the ventral root of a typical segmental 

 nerve is common knowledge. Neal ('14), the most recent contributor to this 

 question, has insisted upon the correctness of this interpretation. He 



* Vide Sherrington, '94a, p. 254. 



t These ganglia (which occur on the roots of the oculomotor just within the brain 

 case) must not be confused with the ciliary ganglia which have sometimes been referred 

 to as oculomotor ganglia. The ciliary ganglia, of course, lie in the orbit and, although 

 connected with the oculomotor (and ophthalmicus profundus) nerves, are generally 

 recognised as being ganglia properly referred to the autonomic (sympathetic) system. 



