470 



G. RYLANDS DE BEER 



The abducens is held to arise from the neural tube by many- 

 roots ; according to Noal four, corresponding to Van VVijhe's 

 somites 3, 4, 5, and G. I have been able to discern three roots 

 which in a 23 mm. embryo arise not very far behind the facial 



Text-fig. 12. 



Ventral view of an embryo 23 mm. long to show the origin of the 



abducens nen^e. 



(Text-fig. 12). In earlier stages their origin appears to be slightly 

 more posterior. It has been suggested that the hypoglossus 

 and abducens roots form a continuous series, implying that the 

 abducens is a compound nerve derived from elements belonging 



