HANDBOOK 



PHYSIOLOGY. 



IV. Hearing. 



Anatomy of the Ear. For descriptive purposes, the Ear, or Organ 

 of Hearing, is divided into three parts, (1) the external, (2) the middle, 

 and (3) the internal ear. The two first are only accessory to the third 



Fig. 395. Diagrammatic view from before of the parts composing the organ of hearing of 

 Ike left side. The temporal boue 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 nieatus externus, half the tympanic membrane, 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. 1, the pinna 

 and lobe: 2, 2', meatus externus; 12'. membrana tympani; 3, cavity of the tympanum; 3', its 

 opening backward into the rnastoil cells; between 3 and 3', the chain of small bones* 4, Eusta- 

 chian 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; 

 b, internal carotid artery; c, styloid process; rf, facial nerve issuing from the stylo-mastoid 

 foramen; e, mastoid process ; /. squamous part of the bone covered by integument, etc. (Arnold.) 



or internal ear, which contains the essential parts of an organ of hear- 

 ing. The accompanying figure shows very well the relation of these 

 divisions, one to the other (fig. 395). 



Kxternal Ear. The external ear consists of i\iQ pinna or auricle 

 and the external auditory canal or meatus. 



The principal parts of the pinna (fig. 395) are two prominent rims 

 inclosed one within the other (helix and antihelix), and inclosing a cen- 

 tral hollow named the concha; in front of the concha, a prominence 

 directed backward, the tragus, and opposite to this one directed for- 

 ward, the antitragus. From the concha, the auditory canal, with a 



