356 PROCEEDINGS OF THE CANADIAN INSTITUTE. 



the lobus inferior which must be r*aised to see its point of emergence. 

 Further up on the lateral aspect of the brain, immediately behind the 

 optic lobe, emerges the fourth nerve (trochlearis). and the posterior 

 tip of the optic lobe must be pushed forwards to see its precise point 

 of emergence. 



The sixth nerve (abducens) leaves the medulla oblongata by two 

 slender strands on each side which take their origin near the ventral 

 longitudinal fissure. All of these nerves after leaving the brain 

 associate themselves with the trigeminus group in a way which neces- 

 sitates the description of their further course with that nerve. 



The trigeminus group not only includes the fifth nerve, but also 

 the seventh. The motor root of the latter is quite distinct from the 

 trigeminal roots, emerging as it does in front of the auditory nerve, 

 and immediately directing itself forward to join the trigeminal com- 

 plex. (Fig. 15, PI. I.) Formerly this motor root was considered 

 to be the only representative of the facial, but first Balfour detected 

 in embryo Selachians a dorsal root taking its course through the 

 orbit, and more recently van Wijhe discovered the part which the 

 R. dorsalis VII plays in the formation of the ramus ophthalmicus 

 stiperficialis. In the adult Amiurus it is impossible to isolate any 

 R. dorsalis VII. from the neighbouring roots of the trigeminus, 

 and I shall consequently only describe the motor root as JV. VII., 

 referring to the others as acustic roots of the trigeminal complex as 

 they take origin from the tuberculum acusticum. 



Curiously Friant has committed the mistake 1 of according solely 

 to these branches (R. buccalis and ophthalmicus superficialis) the 

 name of seventh nerve, and of supposing that their destination is 

 " animer tous les muscles sous-cutane's ou peauciers de la face ainsi 

 que ceux qui entourent l'orifice nasal " ! He describes the proper 

 motor facial as R. hyoideo-mandibularis of the trigeminus. 



In studying the roots of the trigeminal complex after the ganglion 

 has been detached from the brain, Fig. 16, PL I., the two principal 

 roots are readily seen separated by a white band which stretches for- 

 wards from the root of the auditoiy nerve. The upper and more 

 posterior of these, the dorsal geniculated root of the trigeminus 

 (N. V., gen. dors.), can be followed at once into the trigeminal lobe, 

 the lower, which is somewhat anterior in position and considerably 



1 Recherches anatomiques sur les nerfs Tiijumeau et Facial des poissons osseux, Nancy 

 1879. p. 84. 



