THE AUDITORY OSSICLES 



369 



tympanum ; secondly, the long external passage, or 

 m.eatus Fig. 118). 



The drum of the ear and the external meatus, which 

 together constitute the middle ear, would form one cavity 

 were it not that a delicate membrane, the tympanic mem- 

 brane (Ty.M, Figs. 118 and 119), is tightly stretched in an 



Pig. 119.— a Diagram illustrativb of the Relative Positions of 

 THE Various Parts of the Ear. 



S.M, external auditory meatus ; Tv.M, tympanic membrane ; Ty. tym- 

 panum ; Mall, malleus; Inc. incns ; Stp. stapes; F.o, fenestra ovalis : 

 Fr fenestra rotunda; Eu. Eustachian tube; -V.i, membranous laby- 

 rinth, onlv one semicircular canal with its ampulla being represented : 

 Sea. r, Scd.T, Sca.M, the scalae of the cochlea, which is supposed to be 

 unrolled. 



oblique direction acro.ss the passage, so as to divide the 

 comparatively small cavity of the drum from the meatus. 

 The membrane of the tympanum thus prevents any 

 communication, by means of the meatus, between the drum 

 and the, external air, but such a communication is pro- 

 vided, though in a roundabout way, by the Eustachian 



