HEARING. 389 



by the sound of a tuning fork, made to vibrate by 

 striking it against any solid body, being heard 

 more loudly and distinctly when the handle is 

 pressed against the head, and still more so when 

 applied to the teeth, than when not in contact with 

 any part of the head. It is chiefly in this way that 

 a person hears his own voice ; those sounds being- 

 best heard, as Professor Wheatstone remarks, which 

 are principally articulated within the mouth.* 

 Weber concludes from his experiments that the 

 sonorous vibrations conveyed by the cranial bones 

 are communicated more immediately to that por- 

 tion of the auditory nerve which is distributed to 

 the cochlea, while those which are conveyed by 

 the tympanic apparatus are received principally by 

 the nerves of the vestibule. 



§ 3. Comparative Physiology of Hearing. 



The structure of the organs of hearing in the lower 

 animals presents a gradation from the simple vesti- 

 bule, with its membranous sac, supplied with 

 nervous filaments, which may be regarded as the 

 only essential part of this organ, through the suc- 



* He observed that while the sounding tuning fork is placed ou 

 any part of the head, if both ears be closed by being covered witli 

 the hands, a considerable augmentation of the sound takes place. 

 When both ears are open, the sound seems to be heard chiefly by 

 the ear in the vicinity of which the stem of the fork is placed ; but 

 when the opposite ear is closed, it appears as if the sound were trans- 

 ferred from the open to the closed ear ; and if the ear be alternately 

 opened and closed, the sound will appear to be transferred alter- 

 nately from the one to the other. See Journal of the Royal Insti- 

 tution for July, 1827. 



