Oculomotor Nerve in Scyllium canicula. 557 



concludes* " the evidence of its histogenesis and its central and peripheral 

 relations so strongly support the supposition that it is a somatic motor nerve, 

 as the majority of morphologists have believed, that the acceptance of the 

 latter seems unavoidable." 



While Neal is undoubtedly justified in claiming that this view is that held 

 at the present time by the majority of observers, yet, as he points out, this 

 has not always been the case. In the past, many morphologists have main- 

 tained that the oculomotor is serially homologous with the segmental nerves. 

 Comparatively recently this earlier view has been supported by Gast ('09) 

 upon embryological grounds. 



In arriving at his conclusion, however, Neal appears to be altogether unaware 

 of the light which has been shed upon this question by the results of the 

 experimental work of Sherrington and Tozer. 



The Composition of the OculomotorNervc. — Sherrington ('94), as the result 

 of certain experiments upon the eye-muscle nerves, came to the conclusion 

 that the oculomotor might prove to be " sensori-motor " (afferent-efferent). 

 He repeated and laid stress upon this suggestion in a later paper ('97). 



Herrick ('99, p. 230) noted that medullated nerve fibres of two kinds were 

 to be recognised in the oculomotor nerve of a bony fish (Meniclia). He 

 remarked that muscle-spindles were said not to occur in the eye-muscles but 

 suggested that the more slender nerve fibres, whose origin he failed to 

 determine, might, nevertheless, form part of a sensory mechanism analogous 

 with muscle-spindles. 



Eecently the existence of muscle-spindles in the extrinsic eye-muscles has 

 been demonstrated by Sherrington and Tozer ('10). Not only so, but the 

 related spindle nerves were stated to pass into the central nervous system by 

 way of the oculomotor. This, upon the generally accepted interpretation of 

 the oculomotor nerve as merely a ventral root, is altogether anomalous, for 

 the nerve fibres from muscle-spindles in all other muscles are derived from 

 ganglion cells of the dorsal spinal ganglia and thus are connected with the 

 central nervous system only by way of the dorsal (posterior) nerve roots. 



The experimental work carried out by Miss Tozer (12) upon Macacus 

 showed that lesion of the third nerve peripheral to the ganglion cells {i.e., at 

 a point between the ganglion cells and the muscle-spindles) resulted in the 

 alteration of the ganglion cells and the complete degeneration of the muscle- 

 spindles ; whereas, when the lesion was effected centrally to the ganglion, 

 somef at least of the muscle-spindles persisted. 



* Op. tit., p. 105. 



t It should be noted that while only a few muscle-spindles are said to have persisted, 

 in Macacus only a few ganglion cells are normally present. 



