IV. 



THE AUDITORY NERVE AND COCHLEA. 



BY W. WALDEYER. 

 GENERAL VIEW OF THEIR COMPARATIVE ANATOMY AND DEVELOPMENT. 



WHILST the auditory apparatus treated of in the preceding 

 chapter the ssmicircular canals and utriculus already attain 

 their complete development in the majority of Fishes, the 

 second division of the membranous auditory labyrinth the 

 cochlear apparatus is essentially developed as a constituent 

 of the organ of hearing in the higher classes of animals. The 

 cochlear apparatus includes the sacculus, the histological 

 characters of which are analogous to those of the utriculus 

 (see the preceding chapter), and a csecal prolongation of the 

 sacculus the ductus cochlearis. 



The first trace of a ductus cochlearis is exhibited by the os- 

 se >us Fishes, in which, according to the excellent description of 

 Hasse (25), a small projection of the sacculus (fig. 319, 1 0), 

 called by Breschet (5) the cysticula, is to be regarded a.s the 

 rudiment of the cochlea. 



Amongst Amphibia, several portions of the sacculus can be 

 distinguished as belonging to the cochlea, though, with the 

 exception of a small and more independent projection which 

 corresponds to the cysticula of the Fish and the lagena of the 

 Bird, they scarcely rise above the level of the wall of the sac- 

 culus (otolith sac), and rather resemble thickenings of the 

 saccular walls provided with peculiar nerve ends (Deiters, 15; 

 Hasse, 24). 



The cochlear apparatus of Reptiles and Birds is still 

 further developed. In Reptiles, the several divisions of the 



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