v THE SENSE OF HEARING 195 



This brief review of its elements will elucidate the study of 

 the complex peripheral apparatus of audition. We shall study 

 the morphological details more closely later on, in discussing eacli- 

 portion of this apparatus, with the object of bringing out its 

 physiological importance. 



It is easy to show by experiment that the outer and middle 

 ear of man are not of fundamental importance to hearing. If the 

 external auditory passages are stopped, hearing is undoubtedly 

 diminished more to the deeper than to the higher tones of the 

 musical scale, when transmitted through the air. Both, however, 

 can be distinctly perceived through the bones if the sounding 

 body, i.e. a vibrating tuning-forjk, is applied to the skull (mastoid 

 apophysis, forehead, etc.). 



The transmission of sounds and tones occurs normally through 

 the bones when we listen to our own voice. The vibration of the 

 vocal cords throws the bones of the skull into vibration and thus 

 excites the organ of Corti independently of air -transmission 

 through the outer and middle ear. It is an everyday observation 

 that after stopping the auditory meati our own voice sounds much 

 louder. Again, when the head is dipped into water sounds are 

 transmitted through the skull, because the sound-waves of water 

 behave like the sound-waves of solid bodies. 



That the external and middle ear are physical instruments for 

 the improvement of hearing is shown by the fact that the sound- 

 waves of the air are communicated with great difficulty to solid 

 and fluid bodies. That is why on stopping our ears it is very 

 difficult to understand any one speaking in ordinary tones. Apart 

 from the difficulty in the transmission of air-vibrations to the 

 bones of the skull, Einne has shown that hearing is more sensitive 

 when excited through the tympanum than it is when excited 

 through the bones. When the vibrations of a tuning-fork held 

 between the teeth have become so feeble that the ear no longer 

 distinguishes them, they become audible again if the tuning-fork 

 is brought near the external ear. 



When the transmission of sound-waves through the ordinary 

 air-passages becomes impossible owing to disease of the outer and 

 middle ear, there is relatively a very pronounced deafness. 



If the cochlear labyrinth remains sound, this deafness can to 

 some extent be remedied by means of Rhodes' audiphone, which 

 consists of a broad, thin plate, which is brought into connection 

 with the teeth, and thus gathers up the sound-waves from the air, 

 and transmits them to the organs of Corti. 



II. In man the auricle or pinna is an organ of complicated 

 form, but in other mammals it generally takes the shape of a 

 more or less elongated trumpet, usually directed upwards, less 

 often downwards. In the human pinna we must distinguish the 

 helix (which occasionally presents Darwin's tubercle), antihelix, 



