CONDUCTION THKOUGH THE LABYRINTH. 603 



tube suffices, under ordinary circumstances for its complete escape. 

 When increased by disease, however, it may collect in the tym- 

 panum and require catheterization. 



If the tube were permanently open, we should suffer from two 

 great disadvantages. In the first place, at every breath, even 

 during ordinary respiration, some little change in tension of the 

 air contained in the cavity of the drum would occur and impair 

 the hearing ; and secondly, the vibrations of the air in the phar- 

 ynx, produced by the voice, would enter the drum directly, and 

 give rise to an exaggerated shouting noise. 



CONDUCTION THROUGH THE LABYRINTH. 



Every motion of the oval base of the little stirrup bone causes 

 a wave to pass along the liquid in the labyrinth. The bony case 

 of the internal ear being firm, and its contained liquid like 



FIG. 235. 



Diagram of the membranous labyrinth. a, b, c, semicircular canals open- 

 ing into the ventricle d; e, the saccule from which the uniting canal leads 

 into the membranous canal of the cochlea, g. (Cleland.) 



most liquids quite incompressible, the wave travels through all 

 the parts of the internal ear. Through the cochlea it can arrive 

 at the yielding membrane covering in the round opening, which 

 separates the cavities of the tympanum and the cochlea. To 

 pass from the oval vestibular opening which is closed by the 

 stapes, to the inner tympanic membrane which closes the scala 

 tympani of the cochlea, the waves have a very complex route. 

 From the liquid lying around the membranous labyrinth the 



