108 



ZOOLOGY. 



smell, as insects, Crustacea, and mollusca, and in which no 

 special organ of smell has ever been discovered. 



OF THE SENSE OF HEARING. 



222. The apparatus of hearing is very complex, minute, 

 and difficult to describe, and its essential part is enclosed 

 within the rocky portion of the temporal bone (Fig. 61 e). 

 We divide the ear of man into three portions the external 



J 



h g e" e"' f e' b 



Fig. 61. Auditory Apparatus.* 



* Vertical section of the auditory apparatus, somewhat magnified as respects 

 the deeper structures. a, external ear; b, lobe of the ear; c, the eminence 

 called autitragus ; d, concha, continuous with the external auditory canal (f) ; 

 ee, rocky part of the temporal bone ; e 1 , mastoid process ; e", articular cavity 

 for the condyle of the lower jaw; e'", styloid process of the temporal bone ; 

 e"", extremity of the canal by which the internal carotid artery passes into 

 the interior of the cranium; f, auricular canal; <j, membrana tympani; 

 k, cavity of the tympanum; the ossicula auditus have been removed: 

 i, opening in the wall of the tympanum leading to osseous cells ; the fenestra 

 ovalis and rotunda are close to this opening; k, Eustachian tube; /, vesti- 

 bule ; m, semicircular canals; u, cochlea; o, acoustic nerve. 



