MS SPECIAL SENSES. 



brane, which envelops it in a common sheath with the facial. 

 It then penetrates the internal auditory meatus. In its course, 

 it receives filaments from the restiform body, and possibly 

 from the pons Yarolii. "Within the meatus, the nerve divides 

 into an anterior and a posterior branch, the anterior being 

 distributed to the cochlea, and the posterior, to the vestibule 

 and semicircular canals. The .distribution of these branches 

 will be fully described in connection with the anatomy of the 

 internal ear. 



The color of the auditory nerve is grayish, and its con- 

 sistence is soft, thus differing from the ordinary cerebro-spinal 

 nerves, and resembling, to a certain extent, the other nerves 

 of special sense. On the external, or superficial root, is a 

 small ganglioform enlargement, containing fusiform nerve- 

 cells. According to the latest researches, the filaments of the 

 trunk of this nerve consist of very large axis-cylinders, sur- 

 rounded by a medullary sheath, but having no tubular mem- 

 brane. In the course of these fibres, are found small, nu- 

 cleated ganglionic enlargements. 1 



General Properties of the Auditory Nerves. There can 

 be no doubt, as regards the portio mollis of the seventh, that 

 it is the only nerve capable of receiving and conveying to the 

 brain the special impressions produced by waves of sound ; 

 but it is an interesting question to determine, whether this 

 nerve be endowed also with general sensibility. Analogy 

 with most of the other nerves of special sense would indi- 

 cate that the auditory nerves are insensible to ordinary im- 

 pressions ; and this view is sustained by direct experiments, 

 made many years ago. Magendie exposed, in a rabbit, the 

 trunk of the fifth, and the auditory nerve, " and, whenever 

 the fifth pair was touched as lightly as possible, there was 

 evidence of the most acute sensibility, while the animal was 

 passive when the auditory was touched, pressed, or even 



1 WALDETER, in STRICKER, Manual of Human and Comparative Histology^ 

 The Xew Sydenham Society, London, 1873, vol. iii., p. 169. 



