204 



]•'. H. EDGEWOKTil. 



auatomy only, is at variance with the phenomena of develop- 

 ment ; both in Scyllium and Acanthias a well-marked inter- 

 niandibularis is formed in the mandibular segment, and 

 spreads back below the interhyoideus and fusing- with it behind 

 the hyoid bar. Its partial or total innervation by the Vllth 

 must consequently l^e a secondary phenomenon. 



Text-fig. 31. 



The intermaudibularis of Ceratodus is also innervated by 

 the Yllth (Ruge), and its hinder part in Triton (Driiner). 



Ruge held that what is here called the intormandibularis is 

 a facial muscle, and that its innervation from the Vth is 

 secondary, but in Ceratodus, as in all the vertebrates examined, 

 it is developed in the mandibular segment. Ruge's theory 

 was based on the idea that " Es liegt audi nicht der geringste 



