SEVENTH AND AUDITORY NERVES. 42! 



which passes forwards slightly dorsal to the eye and parallel 

 and ventral to a branch of the seventh, which will be described 

 when I come to that nerve. I have been unable to observe that' 

 this branch divides into a ramus superficialis and ramus pro- 

 fundus, and subsequently to stage O I have no observations- on it. 



By stage O the fifth may be observed to have two very 

 distinct roots, and a large ganglionic mass is developed close 

 to their junction (Gasserian ganglion), PI. 17, fig. 4 a. But in 

 addition to this ganglionic enlargement, all of the branches have 

 special ganglia of their own, PL 17, fig. 4 b 



Summary. The fifth nerve has almost from the beginning 

 two branches, the ophthalmic (probably the inferior ophthalmic 

 of the adult) and the inferior maxillary. The superior maxillary 

 nerve arises later than the other two as a branch from the in- 

 ferior, originating comparatively far from its root. There is at 

 first but a single root for the whole nerve, which subsequently 

 becomes divided into two. Ganglionic swellings are developed 

 on the common stem and main branches of the nerve. 



A general view of the nerve is shewn in the diagram in 

 PL 17, fig. i. 



Seventh and A uditory Nerves. There appears in my earliest 

 sections a single large rudiment in the position of the seventh 

 and auditory nerves ; but in longitudinal sections of an embryo 

 somewhat older than stage I, in which the auditory organ forms 

 a fairly deep pit, still widely open to the exterior, there are to 

 be seen immediately in front of the ear the rudiments of two 

 nerves, which come into contact where they join the brain and 

 have their roots still closely connected at the end of stage K 

 (PL 15, figs. 10 and 15 a and 15 b}. The anterior of these pur- 

 sues a straight course to the hyoid arch (PL 15, fig. 10, VII.), the 

 second of the two (PL 15, fig. 10, ait* .), which is clearly the 

 rudiment of the auditory nerve, developes a ganglionic enlarge- 

 ment and, turning backward, closely hugs the ventral wall of the 

 auditory involution. 



The observation just recorded appears to lead to the fol- 

 lowing conclusions with reference to the development of the 

 auditory nerve. A single rudiment arises from the brain for 

 the auditory and seventh nerves. This rudiment subsequently 



