682 THE SENSE OF HEARING. 



heard, even the sound of our own voice, is then much 

 increased in intensity. 



The action of the cartilage of the external ear upon 

 sonorous vibrations is partly to reflect them, and pivily to 

 condense and conduct them to the parietes of the external 

 passage. With respect to its reflecting action, the concha 

 is the most important part, since it directs the reflected 

 undulations towards the tragus, whence they are reflected 

 into the auditory passage. The other inequalities of the 

 external ear do not promote hearing by reflexion ; and, if 

 the conducting power of the cartilage of the ear were left 

 out of consideration, they might be regarded as destined 

 for no particular use ; but receiving the impulses of the 

 air, the cartilage of the external ear, while it reflects a 

 part of them, propagates within itself and condenses the 

 rest, as all other solid and elastic bodies would do. Thus, 

 the sonorous vibrations which it receives by an extended 

 surface, are conducted by it to its place of attachment. 

 In consequence of the connection of the parietes of the 

 auditory passage with the solid parts of the whole head, 

 some dispersion of the undulations will result ; but the 

 points of attachment of the membrana tympani will receive 

 them by the shortest path, and will as certainly com- 

 municate them to that membrane, as the solid sides of a 

 drum communicate sonorous undulations to the parchment 

 head, or the bridge of a musical string, its vibrations to 

 the string. 



Regarding the cartilage of the external ear, therefore, 

 as a conductor of sonorous vibrations, all its inequalities, 

 elevations, and depressions, which are useless with regard 

 to reflexion, become of evident importance ; for those 

 elevations and depressions upon which the undulations 

 fall perpendicularly, will be aifected by them in the most 

 intense degree ; and in consequence of the various form 

 and position of these inequalities, sonorous undulations, 

 in whatever direction they may come, must fall perpen- 



