672 THE SENSE OF HEARING. 



auditory canal, with a slight arch directed upwards, passes 

 inwards and a little forwards to the membrana tympani, 



Fig. 197-* 



to which it thus serves to convey the vibrating air. Its 



* Fig. 197. Diagrammatic view from before of the parts composing 

 the organ of hearing of the left side (after Arnold). The temporal bone, 

 of the left side, with the accompanying soft parts, has been detached 

 from the head, and a section has been carried through it transversely, so 

 -as to remove the front of the meatus externus, half the tympanic mem- 

 brane, the upper and anterior wall of the tympanum and Eustachian 

 tube. The meatus internus has also been opened, and the bony labyrinth 

 exposed by the removal of the surrounding parts of the petrous bone. 

 I . the pinna and lobe ; 2, 2', meatus extemus ; 2', membrana tympani : 

 3, cavity of the tympanum ; 3', its opening backwards into the mastoid 

 cells ; between 3 and 3', the chain of small bones ; 4, Eustachian tube ; 

 5, meatus internus containing the facial (uppermost) and the auditory 

 nerves ; 6, placed on the vestibule of the labyrinth above the fenestra 

 ovalis : a, apex of the petrous bone ; &, internal carotid artery ; c, styloid 

 process ; d, facial nerve issuing from the stylo-mastoid foramen ; e, 

 mastoid process ; /, squamous part of the bone covered by integument, 

 etc. 



