THE AUDITORY NERVE. 



257 



fibres of the mesial root pass mainly to the dorsal auditory nucleus, but some turn 

 inwards to the raphe of the bulb, and others may ascend to the cerebellum either 

 directly or with the intervention of a special nucleus (Bechterew). The fibres of 

 the lateral root end in large part in the accessory or ventral auditory nucleus, which 

 is placed between the two roots in front of the restiform body, and in the ganglion 



Fig. 172. PLAN OP THE ROOTS OP THE TO CEREBELLUM 



AUDITORY NERVE. (G. D. T. ) 



The outline represents a section at the 

 junction of the bulb with the pons : VIII. M. , 

 mesial root, VIII. L., lateral root of the 

 auditory nerve ; N.VIII. ACC. , accessory 

 nucleus ; G.L.R. , ganglion of lateral root ; 

 N.VIII.D., dorsal nucleus of the auditory 

 nerve; A.V, ascending or bulbar root of 

 the fifth nerve. 



of the lateral root ; but a smaller 

 number are continued into the 

 medullary striae and trapezium. 1 



The two roots unite as they leave 

 the medulla oblongata, and the nerve 

 is directed outwards to the internal 

 auditory meatus, in company with 

 the facial nerve, which rests in a 

 groove along its upper and fore part, 

 and the auditory artery, which, 

 together with the portio intermedia 

 of the facial nerve, is placed between 



the two trunks. In the meatus, the nerve divides into an upper smaller and a lower 

 larger part, the fibres of which are continuous with the mesial and lateral roots 

 respectively. The upper or vestilular portion (n. vestibuli), passing above the crista 

 falciformis, divides again into three branches, which are distributed to the utricle and 



Fig. 173. THE AUDITORY NERVE OF THE RIGHT SIDE IN THE IN- 

 TERNAL AUDITORY MEATUS, SEEN FROM ABOVE. (Schwalbe.) f 



The meatus has been opened from above, and the facial nerve 

 removed together with the portio intermedia. The left side of the 

 figure corresponds to the anterior wall of the meatus. 1, superior 

 division ; 2, utricular nerve ; 3, common stem of the superior and 

 external ampullary nerves ; 4, posterior branch of the lower division ; 

 5, saccular nerve ; 6, pcst^rior ampullary nerve; 7, cochlear nerve; 

 8, gangliform enlargement of superior division ; 9, crista falciformis. 



I 



the ampullae of the superior and external semicircular ^..- 

 canals. The tower portion gives off a small posterior branch 

 (middle branch of Schwalbe),which furnishes the nerves of 

 the saccule and posterior semicircular canal, and is then V- 



continued as the cochlear nerve, the subdivisions of 



which enter the apertures in the fossa below the fore part of the crista falci- 

 formis. On the vestibular division of the nerve, in the superior fossa at the 

 bottom of the auditory meatus, is a ganglionic enlargement (intumescmtia ganglio- 

 formis Scarpce, vestibular ganglion), which is continued below into the saccular 

 nerve ; and there are said to be two small swellings on the posterior ampullary nerve 

 in its canal (Corti). The corresponding ganglion of the cochlear nerve is contained 



1 See H. Held, "Die centrale Gehbrleitung," Archiv f. Anat, 1893. 



