234 



Organ of Hearing. 



Ampulla? 



319. The Osseous Labyrinth, 



from before. Magn. = 3. 



The internal ear, the 

 labyrinth, consists of 

 the vestibule, Vestibulum, 

 the three semicircular 

 canals, Canales semicircu- 

 lares, and the Cochlea. 



The vestibule is the 

 central cavity of communi- 

 cation between the semi- 

 circular canals and the 

 cochlea. Its boundaries are : 

 Externally the t y m- 

 panic cavity (the Fene- 

 stra ovalis , by means of 

 which the tympanum and 

 vestibule communciate, is 

 closed by the base of the 

 stapes); internally the 

 internal auditory meatus ; 

 anteriorly the cochlea; 

 posteriorly the semicir- 

 cular canals; superi- 

 orly the commencement 

 of the Fallopian canal 

 (Fig. 327). The anterior 

 portion is called Rccessus 

 hemisphaencus ; the posterior 

 Rccessus liemidlipticus ; be- 

 tween both is the Crista vesti- 

 buli, which ends superiorly 

 with the Pyramis vcstibuli. 

 The three semicircular ca- 

 nals open into the Jftecessus 

 hcmidlipticus by five orifices, 

 two canals at the inner wall 

 of the vestibule having one 



common orifice ; in front of the latter is the orifice of the Aquae- 

 ductus vcstibuli. The Scala vcstibuli of the cochlea opens into the Hecessus 

 hemisphaericus. The three Maculae cribrosae are seen in Fig. 321. 



/Re.cessvs 



Scypli 



Hamulus 



The Osseous Labyrinth, 



laid open from before. Magn. = 3- 



