7'4 



TEXT-BOOK OF PHYSIOLOGY 



membrane covered with ciliated epithelium. Near the middle of its course 

 the tube is contracted, though expanded at either extremity (Fig ,17) 

 measures about 40 mm. in length. Its general direction from fhe pharyn- 

 de rees * UtWard> backward ' an d upward at an angle of about 45 



The middle ear cavity is separated from the external ear by a membrane 



-the membrana tympani-and from the internal ear by an osseo- 



membranous partition which forms a common wall for both cavities 



The interior of the cavity is crossed from side to side by a chain of 



hTnx a mUC US membrane continuous with that lining the 



The Membrani Tympani.-Tte membrana tympani, is a thin, translucent 

 nearly circular membrane, measuring about 10 mm. in diameter, placed at 



the inner termination of the external auditory canal. It is inclosed in a ring 



ctdMon W r TK 6 fCtal T did n Can be easi 'y removed - but in the adult 

 idition cannot be removed, owing to its consolidation with the surrounding 



This membrane consists primarily of a layer of fibrous tissue which 

 uoCv r eXt f rna "y ^ a thm layer of skin continuous with that lining the 

 iitory canal and internally by a thin mucous membrane. The tympanic 

 membrane is pkced obliquely at the bottom of the auditory canal, Liming 

 five def andbehmd downward and forward at an angle of about forty 5 

 five degrees. The external surface of this membrane presents a funnel- 

 shaped depression, the sides of which are slightly convex 



mfwif T"'~^T ning . aCr SS the ^P* cavity and forming an 

 gular line of joined levers is a chain of bones, which articulate onelith 



