62 H. V. NEAL 



various cell elements derived from different sources has been 

 found. The clusters of ganglion (?) cells associated with the 

 trochlear anlage, which the writer interprets as homologous with 

 sympathetic ganglia, are clearly derivatives of the superficialis 

 nerve and not migrant medullary elements. Most of the cells 

 associated with the anlagen of the eye-muscle nerves may be 

 traced into the neurilemma cells of the differentiated nerves. 

 Their gradual penetration into the fiber bundles of the anlagen, 

 beginning with their proximal and distal extremities, may be 

 easily followed in successive stages. 



The nidulus of the oculomotor is limited to the somatic motor 

 column of the midbrain vesicle (neuromere II) and presents no 

 evidence of subdivision into two or more niduli. The nidulus 

 of the trochlear lies in the somatic motor column of the first 

 hindbrain neuromere (neuromere III). That of the abducens 

 is post-otic and extends through two post-otic neuromeres (VII 

 and VIII). These relations afford important clues to the prim- 

 itive segmental relations of the e3^e muscle nerves, and present 

 an insuperable difficulty to the hypothesis that the eye muscles 

 have migrated into their present relationships from a post-otic 

 source. 



2. Does the histogenesis of the ocvlomotorius resemble that of a 

 somatic motor spinal nerve? 



a. Are the muscle and nerve, that is, midbrain and somite 1 of 

 VanWijhe, connected with each other ab initio? Among the opin- 

 ions in regard to the histogenesis of the oculomotor nerve no 

 one has maintained upon an observational basis that the nerve 

 is ab initio connected with the first somite of VanWijhe. Not 

 even Sedgwick ('94), who regarded himself as a supporter of 

 the Hensen theory of the primary connection of nerve and mus- 

 cle, was able to maintain this view by the histogenesis of the 

 oculomotor; for he stated that the oculomotor ''is differentiated 

 from the ciliary ganglion to the floor of the midbrain." It ap- 

 pears, therefore, justifiable to infer — in view of the failure of 

 all students of this much investigated nerve to demonstrate a 



