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 
R. mandibularis v., but this soon separates out again. 
Just opposite sense organ J, the external mandibular 
perforates the dentary and thereafter lies over the roof of 
the hyomandibular canal. The anterior free portion of 
the external mandibular supphes the first 5 sense organs 
of the hyomandibular canal. 
We may 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. |j, «=Ahe yentrall ,; -f second 
Fourth ,, =the communis root Tone 
Fifth ,, = our third or the motor vu. 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 R. palatinus vii. has a discrete opening in the 
skull is of course an error. 
Nervus Acusticus—VIII. (Fig. 24.) 
The ear is described with the other sense organs. 
All the fibres of the auditory nerve (vili.) arise from 
the same region of the brain (tuberculum acusticum) as 
the lateral line fibres. The two sets of fibres form a very 
