Growth and Differentiation in the Ner 



[ervous System 277 



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PLATE II. Fig. 12. Transverse section through the Vlth nerve of a 6-day embryo. 

 Arrow points to neuroblasts in the process of migrating from the main nucleus (a) 

 of the Vlth nerve to the accessory nucleus (6) of the same nerve, c, neuroblasts 

 of the Vllth nucleus. FIG. 13. Transverse section at the same level as Fig. 12. in 

 an 11-day chick embryo. The migration of the accessory nucleus (6) from the main 

 nucleus (a) of the Vlth nerve is completed, c, Vllth nucleus. Fig. 14. Transverse 

 section through the nuclei of the Illrd nerve at the mesencephalic level of a 6-day 

 embryo. The arrow points to the two populations (a and a') as they cross the mid- 

 line and move in opposite directions to join the nuclei of the contralateral lllrd 

 nerve. FIG. 15. 15-day embryo. Cross section at the same level as in Fig. 14. The 

 two ventromedial nuclei of the Illrd nerve (« and «') are seen in their definitive 

 contralateral position. Note the segregation of the oculomotor nerve cells in four 

 nuclei. 



