134 



11. R. mandibularis externus {man. ext. vii.). — A 

 coarse-fibred lateral line nerve, but contains some fine 

 fibres. In front is joined by a fine-fibred nerve from the 

 E/. mandibularis v., but this soon separates out again. 

 Just opposite sense organ 3, the external mandibular 

 perforates the dentary and thereafter lies over the roof of 

 the hj'Omandibular canal. The anterior free portion of 

 the external mandibular supplies the first 5 sense organs 

 of the hyomandibular canal. 



We niaj now refer very briefly to the statements of 

 Stannius on the trigeminal and facial nerves of the Plaice. 

 His analysis of the roots of these two nerves is given, in 

 great detail (pp. 23-25), and is remarkably accurate con- 

 sidering the methods at his disposal. His five roots cor- 

 respond with ours as follows: — 



First Root = our first or trigeminal root (cutaneous + 



motor) 



Second , , = the dorsal lateral line root | of our 



Third „ = the ventral „ „ 'second 



Fourth ,, = the communis root 



Fifth ,, = our third or the motor vii. root. 



His statement that branches of the superior maxillary 

 anastomose with the palatinus vii., and are distributed to 

 the mucous membrane of the mouth, points to a communis 

 component in the former nerve. He describes our nerve 

 called the R. lateralis recurrens vii., but his statement 

 that the E,. palatinus vii. has a discrete opening in the 

 skull is of course an error. 



N e r V u s A c u s t i c u s — VIII. (Fig. 24.) 



The ear is described with the other sense organs. 



All the fibres of the auditory nerve (viii.) arise from 

 the same region of the brain (tuberculum acusticum) as 

 the lateral line fibres. The two sets of fibres form a very 



