528 



THE AUDITORY APPARATUS 



tympanum. In the anterior part of the medial wall of the 

 vestibule there is a circular depression, termed the recessus 

 sphcericus \ it is bounded posteriorly by a vertical ridge, 

 called the crista vestibuli. In the bottom of the recessus 

 sphaericus are some minute holes through which pass 

 filaments from the acoustic nerve. In the roof of the 

 vestibule is another depression, named the recessus ellipticus. 

 It is placed posterior to the crista vestibuli. 



A small aperture in the posterior part of the medial 

 wall also deserves mention. It is the mouth of the aquce- 

 ductus vestibuli a small canal which passes backwards to 



Recessus ellipticus 

 Crista vestibuli 

 Recessus sphaericus 



Lateral semi- 

 circular canal 



Posterior semi- 

 circular canal 



Scala tympani 

 Lamina spiralis ossea j 

 Scala vestibuli 



Opening of 



aquaeductus cochleae I j Opening of crus commune 



Fenestra cochleae I 

 Recessus cochlearis P enin S of aquaeductus vestibuli 



FIG. 223. Interior of the Left Bony Labyrinth viewed from 

 the lateral aspect. (Howden. ) 



the posterior surface of the petrous part of the temporal bone, 

 where it opens under the dura mater. 



Canales Semicirculares Ossei. There are three bony semi- 

 circular canals or tubes placed posterior to the vestibule. 

 They are bent upon themselves, so that each forms consider- 

 ably more than half a circle, and they occupy planes at right 

 angles to each other like three faces of a cube. They are 

 termed superior, posterior, and lateral, and they open into 

 the posterior part of the vestibule by five round orifices, the 

 number of openings being reduced to five because the 

 adjoining extremities of the superior and posterior canals 

 are fused into a common canal called the crus commune, 

 which opens by a single orifice. One extremity of each 

 canal where it joins the vestibule becomes expanded into 



