266 ANIMAL PHYSIOLOGY. 



performer were to show any movement in his face indicating 

 speech; but, nevertheless, his voice proceeds from his larynx, 

 and the words are formed by the organs of speech, and the 

 effect is produced entirely by imitation and persuasion. 



The precise mode of action of the cochlea is as little deter 

 mined as that of the semicircular canals. It is rudimentary 

 in birds, and in its spiral form is peculiar to mammals. It 

 may fairly be assumed that by this part of the ear we become 

 cognizant, not only of pitch, but likewise of the quality or 

 timbre of sounds, seeing that it has been discovered that 

 timbre depends on the mixture, with a principal note, of a 

 great variety of others in consonance with it. But the mode 

 in which the characters of sounds are preserved unaltered in 

 their passage to the cochlea, and the reason why the rods of 

 Corti get longer as the diameter of the cochlea gets narrower, 

 are subjects for further investigation. It cannot be doubted 

 that the vibrations of the hairs, projecting from nucleated 

 cells, are those which immediately affect the auditory nerve, 

 and that they are produced by vibration of the walls of the 

 membranous canal, but there is no evidence as to the part 

 played by the rods of Corti. It ought not to be lightly 

 assumed that they strengthen sound; they may possibly act 

 as dampers, to check reverberation. 



