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



following "accessory optic vesicles," the dorsal roots would undergo con- 

 siderable diminution in size and importance. The dorsal ganglia, from which 

 most of the remaining afferent fibres would have arisen, would consist of 

 comparatively few cells (the large contingents of cells, normally present in 

 ganglia upon nerves supplying regions of less specialisation, being altogether 

 wanting). 



Gast has stated that a transient dorsal root, related to the oculomotor, 

 appears in development, and considers that this and other eye-muscle nerves 

 represent segmental nerves from which the sensory elements have altogether 

 disappeared. 



Neal, dissenting entirely from Gast's speculation, remarks ('14, p. 105) : 

 " The supposed demonstration of the participation of sensory elements in the 

 genesis of the oculomotor is one that would satisfy only on the basis of 

 a strong presumption in its favour." I would suggest that the actual 

 occurrence, in Macacus rhesus, Columba lima, Gadus virens, and Scyllium 

 canicula, of numerous ganglion cells in the oculomotor roots, apparently 

 related to afferent nerve fibres connected with sensory end-organs, supplies 

 the " strong presumption " which Neal requires. Neal continues, " The 

 position of the nidulus of the oculomotor and its peripheral distribution 

 create a strong presumption against the assumption. Spindle-shaped cells 

 lying in the mesenchyma between the profundus ganglion and the oculo- 

 motor nerve are not necessarily neuroblasts. Spindle-shaped cells may be 

 found almost anywhere in the mesenchyma. Even if it be admitted that 

 the evidence that these cells are in the process of migration towards the 

 oculomotor anlage is convincing, Gast does not know their fate. They may 

 form neurilemma or they may enter the sympathetic or what-not." Is it 

 not reasonable to suppose that the cells of the oculomotor ganglion may 

 represent some of the sensory elements which take part, according to Gast, 

 in the formation of the oculomotor anlage ? 



If others of these cells migrating to the oculomotor should subsequently 

 " enter the sympathetic " as Neal suggests, it would strengthen rather than 

 weaken the case for regarding the oculomotor as a segmental nerve. Neal 

 himself states ('14, p. 57) that neural crest cells do come into connection 

 with the oculomotor anlage and do apparently, amongst other destinations, 

 arrive ultimately at the sympathetic (ciliary) anlage. Indeed, Neal makes 

 use of this fact to support his contention that spinal sympathetic ganglia 

 have an origin from dorsal spinal ganglia, by analogy with this development 

 of the ciliary ganglion. 



The Displacement of Dorsal Boots. — The dorsal roots of cranial nerves 

 practically always shift ventrally from their primary position, during the 



