THE ORGAN OF HEARING. 



439 



ear or labyrinth. It is lined by a mucous membrane 

 and contains the bones of the ear, malleus, incus, and 

 stapes. The mucous membrane is folded over these 

 ossicles and has a pseudostratified ciliated epithe- 

 lium, having two strata of nuclei. Cilia are, how- 

 ever, absent on the surface of the auditory ossicles, 

 their ligaments, and the tympanic membrane. The 



Fig. 302. Semidiagrammatic section through the right ear: G, Exter- 

 nal, auditory meatus; T t membrana tympani; P, tympanic cavity; o, 

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

 VI, scala vestibuli; Pt t scala tympani (Czermak.) 



tympanic cavity communicates with the mouth by 

 a narrow canal, the Eustachian tube, which transmits 

 air and conveys mucous secretion from the middle 

 ear. This tube is about one and one-half inches in 

 length and is directed downward and inward from 

 the anterior part of the tympanum to open on the 



