SENSE OF HEARING. 



903 



The fenestra rotunda is not to be considered as having any peculiar relation 

 with the cochlea ; since, in the Turtle tribe, the former exists without the 

 latter. 



905. It is obviously in the Labyrinth, as a whole, that the sonorous vibra- 

 tions are brought to bear upon the Auditory nerve spread out to receive them. 



Fig. 224. 



The soft parts of the Vestibule taken out of their bony case, so as to show the distribution of the Nerves 

 in the Ampullae : 1, the superior semicircular membranous canal or tube ; 2, the external semicircular tube ; 

 3, the inferior semicircular tube ; 4, the tube of union of the superior and inferior canals ; 5, the sacculus 

 ellipticus; 6, the sacculus sphericus ; 7, the portio dura nerve; 8, the anterior fasciculus of the auditory nerve ; 

 9, the nerve to the sacculus sphericus ; 10, 10, the nervous fasciculi to the superior and external ampullae ; 

 11, the nerve to the sacculus ellipticus ; 12, the posterior fasciculus of the auditory nerve, furnishing, 13, the 

 filaments of the sacculus sphericus, and, 14, the filaments of the cochlea, cut off. 



In regard to the special functions of particular parts of the labyrinth, however, 

 no certainty can be said to exist. The membrane which lines its cavities not 



Fig. 225. 



The Ampullae of the External Semicircular Membranous Canal, showing the mode of termination of its 

 Nerve. 



