MORPHOLOGY OF EYE MUSCLE NERVES 77 



throw any light upon the primitive relations of these nerves in 

 vertebrates. Johnston's inference is fallacious since his premise 

 is incorrect. The cells of the ciliary ganglion of Squalus are pro- 

 liferated from the medial surface of the profundus ganglion. It 

 may be granted, however, that the demonstration that the ' tha- 

 lamic nerve ' represents the primitive root of the profundus nerve, 

 would associate this so-called nerve with the ciliary ganglion as 

 its sympathetic visceral sensory component. 



Sections of Squalus embryos give convincing evidence of cellu- 

 lar migration, both from the midbrain and from the mesocephalic 

 ganglion, into or towards the oculomotor anlage, but it is impos- 

 sible to feel convinced that the migration of the medullary cells 

 extends as far as the ciliary ganglion. In fact the evidence of 

 the participation of medullary cells in the formation of the sym- 

 pathetic is as doubtful in the case of the oculomotor as in the case 

 of spinal somatic motor nerves. The possibility of such a de- 

 rivation can not be denied, but positive demonstration on the 

 basis of evidence obtained from serial sections has not yet been 

 given. In this respect, that is, in the derivation of its proper 

 sympathetic ganglion, the oculomotor resembles a spinal somatic 

 motor nerve. 



j. Summary of the histogenesis of the oculomotor and of the cili- 

 ary ganglion. In all essential respects, the oculomotor nerve re- 

 sembles in its histogenesis a spinal somatic motor nerve, i.e., 

 in its appearance as a product of the protoplasmic movement of 

 medullary neuroblasts situated in the somatic motor column of 

 the neural tube ; in its secondary connection with a mesodermic 

 somite. Van Wijhe's first; in the growth and extension of its fibers 

 by the continuous movement of the protoplasm of medullary neu- 

 roblasts; in the differentiation of its neurofibrils within the pro- 

 toplasm of these processes; in the migration of medullary cells 

 into the nerve anlage to form — at least in part — the neurilemma; in 

 the probability of the participation of mesenchymatous cells in 

 the formation of the neurilemma; in its union with cells of a cerebro 

 spinal ganglion ; and finally in its association with a sympathetic 

 ganglion, the ciliary, derived mainly if not exclusively, from a 

 cerebro-spinal ganglion as a result of cellular migration. 



