MORPHOLOGY OF EYE MUSCLE NERVES 73 



On the other hand, Carpenter ('06) gives convincing reasons 

 for thinking that some of the migrant medullary cells from the 

 midbrain participate (as a group of smaller cells easily distin- 

 guishable from the larger ganglion cells derived from the meso- 

 cephalic ganglion of the chick) in the formation of the ciliary 

 ganglion. If this conclusion be confirmed — and this has been 

 done by Belogolowy ('10) — it appears, that at least some of the 

 medullary cells in the oculomotorius anlage are neuroblastic. 



Gast ('09) is not able to confirm Carpenter's conclu- 

 sion that some of the migrant medullary elements enter into 

 the formation of the neurilemma, biit is of the opinion that the 

 neurilemma is formed by migrant cells from the mesocephalic 

 ganglion which travel centrad along the nerve anlage as far as 

 the roots by which it arises from the brain and thence they 

 migrate back again into the nerve to become the neurilemma 

 cells. As has been stated above. Cast's evidence of this forward 

 and back migration does not appear very convincing. Analogy 

 with the derivation of the neurilemma of motor roots in higher 

 vertebrates from the sensory ganglia with which they are con- 

 nected does not prove such a derivation in selachians. 



That the migrant medullary elements participate in the for- 

 mation of the neurilemma seems to Carpenter evinced by the 

 following considerations: '^Many of these nuclei, once out 

 on the nerve, become elongated as they move away from the 

 neural tube," and "maintain throughout development their 

 close proximity to the nerve fibrils." Again, the absence of 

 evidence of the intrusion of cells from the mesenchyma is further 

 indication of the ectodermal origin of the neurilemma. Further- 

 more, analogy with the differentiation of the neuroglia elements 

 within the central nervous system points in the same direction. 

 Finally, Carpenter was able to trace these cells through suc- 

 cessive stages until they were, in structure and relations, demon- 

 strably the neurilemma elements of the differentiated nerve. 

 I reached similar conclusions ('03) for the derivation of the 

 neurilemma of spinal somatic motor cells. The evidence appears 

 to warrant the inference. Even Kolliker, who for years main- 



