LABYRINTH 



529 



what is termed its ampulla. There are, therefore, three 

 ampullated ends. 



The superior semicircular canal forms the highest part of 

 the labyrinth. Its highest part lies beneath the eminentia 

 arcuata on the anterior surface of the petrous part of the 

 temporal bone. It is placed vertically, and is almost trans- 

 verse to the long axis of the petrous part of the temporal 

 bone. The posterior semicircular canal, which is the longest 

 of the three tubes, is also vertical, and lies in a plane parallel 

 to the posterior surface of the petrous part of the temporal 

 bone. The lateral semicircular canal is the shortest of the 



Superior semicircular canal 

 with its ampulla 



Canalis 

 facialis 



Cochlea | 



Fenestra cochleae 



Fenestra vestibtil 



Ampulla of posterior semicircular canal 

 Ampulla of lateral semicircular canal 



Posterior semi- 

 circular canal 

 Crus commune 



Lateral semicircular canal 

 FIG. 224. Left Bony Labyrinth viewed from lateral side. (Howden. ) 



tubes. It lies in a horizontal plane, in the angle between 

 the superior and posterior canals. 



Cochlea. The cochlea is a tapering tube which is coiled 

 spirally, for two turns and a half, around a central pillar, termed 

 the modiolus. The appearance produced is somewhat similar 

 to that of a spiral shell. The cochlea lies anterior to the 

 vestibule ; its base is directed towards the bottom of the in- 

 ternal acoustic meatus ; its long axis runs antero - laterally 

 from the base, and its apex lies in close relation with the 

 canal for the tensor tympani muscle. 



The cochlear tube rapidly diminishes in diameter as it 

 is traced towards the apex of the cochlea. Its closed ex- 

 tremity is termed the cupola. The first turn which the 

 cochlea takes around the modiolus produces the bulging on 



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