THE NERVOUS SYSTEM 139 



to the lateralis system and has nothing to do with the trigeminus 

 system at all, it being a larval structure which disappears at meta- 

 morphosis. The only trace of this system of nerves to be found in 

 the adult is a very fine connexion between the acustico-facialis gang- 

 lion and the Gasserian ganglion — the remains of the Radix dorsalis 

 of von Plessen and Rabinowicz — the whole of the ganglion with its 

 R. ophthalmicus superficialis VII (R. frontalis, v. P. and R.), R. 

 buccalis (R. supramaxillaris superior, v. P. and R.), and R. mandi- 

 bularis externus (R. buccalis, v. P. and R.) having atrophied, with the 

 possible exception of a few fibres distributed to the skin above the 

 M. levator mandibulae which may represent the remains of the R. 

 ophthal. super. VII (cf. Driiner, 1901, p. 537). 



We may now consider the three main rami of the Vth nerve. 



Vj. R. ophthalmicus profundus (m.5a) (general cutaneous). (See 

 also PL XIII, fig. 57.) 



R. nasalis . ..... von Plessen and Rabinowicz. 



R. ophthalmicus ........ Hoffmann. 



Comparing this ramus with the typical Selachian arrangement, it 

 probably represents both the ophthalmicus profundus and at least 

 a portion of the ophthalmicus superficialis V of that group, but since 

 almost the whole of the nerve passes ventral to the M. rectus sup. it 

 seems justifiable to apply the term 'profundus' to it. 



After leaving the ganglion it passes out from the For. pro-oticum, 

 lateral to the orbito-sphenoid cartilage s. trabecula, but mesial to the 

 ascending process of the quadrate. (It is thus separated by this pro- 

 cess from the other two trigeminal branches.) It then passes directly 

 anteriorly, mesial to the levator muscles of the mandible, between 

 the R. sup. and the R. inf. of the N. oculomotorius, ventral to the 

 M. rectus superior, dorsal to the optic nerve, and between the eyeball 

 and the skull. During its passage through the orbit it gives of? 

 several — usually three — branches to the skin on the dorsum of the 

 head. There is a great deal of individual variation in the precise 

 arrangement of these branches, but the following seems to be the one 

 most generally met with. It differs slightly from that given by Hoff- 

 mann, but the difference is more apparent than real, as this author 

 seems to be describing one particular case as if it were a rigid plan 

 adhered to by all individuals. 



(i) The first branch (V^^'+V^^\ Hoffmann) probably represents 

 the R. temporalis superior (Gaupp) of the Frog. It arises from the 

 main stem before it crosses the N. oculomotorius. It passes dorsal 



