THE ORGANS OF SPECIAL SENSE 263 



whole of the interior of the mastoid process and part of 

 the petrous portion of the temporal bone. They com- 



FlG. 138. Semidiagrammatic section through the right ear : G, external 

 auditory meatus; T, membrana tympani ; P, tympanic cavity; o, fenestra 

 ovalis; r, fenestra rotunda; B, semicircular canal; S, cochlea ; Vt, scala 

 vestibuli; Pt, scala tympani (Czermak). 



municate with the upper and posterior circumference of 

 the tympanum by a large irregular opening. 



FIG. 139. The small bones of the ear ; external view (enlarged) (after Gray). 



The Eustachian tube is a canal of communication, ex- 

 tending obliquely between the pharynx and the anterior 



