62 MORPHOLOGY OF THE ORGANS OF VERTEBRATES. 



largely sensory, most of the motor fibres, together with sensory, 

 going to branch c. Each of these branches may have a secon- 

 dary ganglion connected with it, the ciliary ganglion on a, 

 the sphenopalatine on b, and the otic on c. 



In many ichthyopsida the seventh nerve is closely connected 

 with the fifth, and by mere dissection- the roots of the two can- 

 not be distinguished. 1 In the higher vertebrates the two nerves 

 are distinct throughout. The facialis is more complicated than 

 the trigeminal, and may contain four components. In the lower 

 vertebrates it is a mixed nerve, but in the higher it is purely 



vnb- 



m 



FIG. 64. Diagram of the relations of the fifth (shaded), seventh, and eighth 

 nerves in an aquatic amphibian, after Strong, b, buccalis ; ga, auditory ganglion ; 

 gg, Gasserian ganglion ; gp, palatine ganglion ; h, hyoid nerve ; m, mandibular nerve ; 

 mx, superior maxillary nerve ; op, ophthalmicus profundus; os, ophthalmicus super- 

 ficialis ; /, palatine nerve ; VII a, aa, ab, the three roots of the seventh nerve j 

 VIII, root of auditory nerve; IX, communication of seventh with ninth nerve 

 (Jacobson's commissure). 



motor, and is connected largely with the muscles of expression. 

 In its greatest development (ichthyopsida) it gives rise to four 

 branches, a, ophthalmicus superficialis ; ' 2 b, hyomandibularis ; 

 c, buccalis ; and d, palatinus. The first of these has its own 

 ganglion and is purely sensory, supplying the lateral line organs 

 (see sense organs, infra) on the top of the head. It is found 

 only in aquatic ichthyopsida, the frog, for instance, losing it at 



1 Microscopic study shows that they are usually as distinct here as in the higher forms. 



2 Fibres from the fifth accompany the ophthalmicus superficialis. 



