MIGRATION IN THE ABDUCENS 



5 DAYS 



6 DAYS 



VI A 



VI B 



II DAYS 



FIG. 2. Diagrammatic frontal and transversal representation of the segregation of 

 the accessory nucleus from the main nucleus of the Vlth nerve in the chick embryo. 

 a, b, c: slereographic views of the Vlth nuclei at 5. 6, and 11 days. In a, the nuclei 

 appear as two columns; in b, the arrows indicate the migration of neuroblasts 

 from the main nuclei in a lateral direction; in c, the migration is completed and 

 the two accessory columns are formed, a', b', c' : the same process as viewed in 

 transversal sections. VI A, main nucleus; VI B, accessory nucleus. 



270 



