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



observers. Kecently Carpenter ('06), Gast('09), and Belogolowy ('10) have 

 confirmed this, but the two latter authors suppose that these migrant neural 

 crest cells simply become neurilemma and supporting cells in the oculo- 

 motor root. 



Johnston ('05, p. 244) believed that the cells of the ciliary ganglion arose 

 from a part of the neural crest distinct from that which gave rise to the 

 profundus ganglion. Neal denies that this is true for Squalus, but makes a 

 very interesting statement concerning the origin of the ciliary ganglion in 

 that form. ". . . the first clusters of cells associated with the anlagen of 

 these nerves (the oculomotor and the trochlear) are derived from the neural 

 crest. These cell clusters, in their relations and— in the case of the ciliary — 

 in their adult structure, appear to be sympathetic. Their derivation from 

 the neural crest favours the inference that the sympathetic anlagen of the 

 trunk have a similar origin " ('14, pp. 58-59). 



From all of which, indefinite and conflicting as it appears, three facts 

 emerge : — 



(i) that, in the anlage of the oculomotor, cells are found derived by migra- 



tion (a) from the medulla, and (b) from the neural crest ; 



(ii) that certain of these cells in the oculomotor anlage migrate into the 

 anlage of the ciliary ganglion, precisely as do cells from a typical 

 dorsal ganglion into a typical sympathetic ganglion; 



(iii) that the weight of evidence appears to be against the belief that cells 

 of medullary origin contribute to the formation of sympathetic 

 ganglia. 



The inference is that the cells which pass along the oculomotor to the ciliary 

 ganglion must have been derived, in the first instance, from the neural crest. 



The Comparison of the Oculomotor with a Complete Segmental Nerve. 



In view of what has been said it will be obvious that, in certain particulars, 

 the peripheral relations of the oculomotor are not exactly those of a ventral 

 root. Nor does it appear that the histogenesis of this root (in its relation 

 to the neural crest and the ciliary ganglion) corresponds, in every particular, 

 with that of a spinal ventral root. In attempting to arrive at a correct 

 interpretation of the homology of the oculomotor we must take into account 

 the following facts : — 



(i) that this nerve is undoubtedly " afferent-efferent " ; some or all of its 



afferent fibres being related to sensory end-organs (muscle-spindles) ; 



(ii) that, upon its root, in some forms, occurs a ganglion or scattered 

 ganglion cells ; 



