408 



THE ORGANS OF SPECIAL SENSE 



upward and then downward. It is narrowest at its 

 middle. It opens externally by means of the external 

 auditory meatus. 



The Middle Ear or Tympanum. This is a cavity in 

 the petrous portion of the temporal bone, extending 

 from the membrana tympani to the outer wall of the 

 labyrinth. Its width varies from T V to ^ inch. It 

 contains the ossicles of the ear, with their ligaments 

 and muscles, and certain nerves. It is filled with air 

 and communicates by means of the Eustachian tube 

 with the nasopharynx. 



FIG. 142 



Cartilage of 



the pi Hint ~ 



Promont. 



Int. carat, a. 



Membrana / 

 tympani / 



* Cartilage of the cxt. 

 and/tori/ /itcafiix 



Transverse section of external auditory meatus and tympanum. (Gegenbaur ) 



The membrana tympani is a thin membrane inserted 

 into a ring of bone at the bottom of the external 

 canal, which is grooved for its reception. It is ovoid 

 in form and directed obliquely downward and inward. 

 On its inner surface is the handle of the malleus, which 

 extends from about the middle of its roof to a little 

 below its centre, covered by mucous membrane, where 



