566 



THE AUDITORY APPARATUS 



osseous chambers, and the intervening space is filled with a 

 fluid termed the perilymph. The membranous labyrinth also 

 contains a fluid which receives the name of endolymph. 



Vestibulum. The vestibule is a small ovoid bony chamber, 

 possessing an antero- posterior diameter of about one- sixth 

 of an inch. It is situated between the medial wall of the 

 tympanum and the bottom of the internal acustic meatus. 



Into the posterior part of the vestibule the three semi- 

 circular canals open by five round apertures; whilst in its 

 lower and anterior part is the opening of the scala vestibuli 

 of the cochlea. 



Recessus ellipticus 

 Crista vestibuli 

 Recessus sphaericus 



Superior semi- 

 circular canal 



Scala tympan 

 Lamina spiralis ossea 

 Scala vestibuli 



Opening of 

 aquaeductus cochleae 



Fenestra cochleae 

 Recessus cochleari 



Posterior semi- 

 " circular canal 



Opening of crus commune 

 Opening of aquaeductus vestibuli 



FIG. 248. Interior of the Left Bony Labyrinth viewed from 

 the lateral aspect. (Howden. ) 



On the lateral waU\$> the fenestra vestibuli, which is closed, 

 in the recent state, by the delicate periosteal lining of the 

 chamber and the base of the stapes. When these parts are 

 removed, the vestibule communicates directly with the tym- 

 panum. On the- anterior part of the medial wall of the 

 vestibule there is a circular depression, termed the recessus 

 spharicus, which is bounded posteriorly by a vertical ridge, 

 called the crista vestibuli. The bottom of the recessus sphaericus 

 is perforated by some minute holes which give admission to 

 filaments from the acustic nerve. On the roofoi the vestibule 

 is another depression, named the recessus ellipticus. It is placed 

 posterior to the crista vestibuli. 



A small aperture placed on the posterior part of the 

 medial wall also deserves mention. It is the mouth of the 

 aquceductus vestibuli a small canal which leads posteriorly to 



