SENSE OF HEARING. 



257 



laginous, but hard and stony in the Osseous tribes; to these the name of Oto- 

 lithes has been given. Some rudiments of a tympanic cavity may be found 

 in Fishes; but there is no vestige of a cochlea; in several tribes, the organ 

 of hearing possesses a peculiar connection with the air-bladder, which appears 

 to be a foreshadowing of the Eustachian tube of higher classes. 



351. In the true Reptiles, a considerable advance is constantly to be found 

 in the character of the Ear; a tympanic cavity being added, with a drum and 

 a chain of bones ; and a rudiment of the cochlea being generally discoverable. 

 Among the Amphibia, however, which are in so many respects intermediate 



[Fig. 48. 



An imaginary figure or plan of the Cochlea; this figure is designed to show how the twoscalaeof the coch- 

 lea communicate in its summit ; the parietes of the scala vestibuli are supposed to be removed ; 1. 1, the 

 osseous portion of the lamina spiralis; its small end is the hamulus cochleae; 2, 2, the dark ground here 

 represents the membranous portion of the cochlea or the zona membranacea; 3, the commencement of the 

 scala tympani ; 4, its external edge; 5, its internal edge ; 6 corresponds to the modiolus around which the 

 lamina spiralis is wound ; 7, its summit; 8, the point of communication 9f the two scalae.] 



[Fig. 49. 



A view of the axis of the Cochlea and the Lamina Spiralis, showing the arrangement of the three Zones 

 the osseous zone and the membrane of the vestibule have been removed; 1, the natural size of the pans; 

 the other figure is greatly magnified; 2, trunk of the auditory nerve ; 3, the distribution of its filaments in 

 the zona ossca; 4, the nervous anastomosis of the zona vesicularis; 5, the zona membranacea ; 6, the 

 osseous tissue of the modiolus ; 7, the opening between the two scalce.l 



22* 



