CHAPTER IX 



THE EAR AND THE SENSE OF HEARING 



167. The ear is the mechanism by which we hear. It 

 has three main divisions, called the external, the middle, 

 and the internal ear (Fig. 74). 



Endolymphatie 

 Duct 



,'Saccule 

 ' 



"estibular Passage 

 ^Tympanic Passage 

 Eustachian Tube Fenestra Rotunda 



Fig. 74. Diagram of the ear, showing relationship of its parts. 



168. The External Ear. The parts of the external ear 

 are formed to collect and conduct waves of sound to the 

 inner portions of the auditory apparatus. They are the 

 pinna, the external meatus, and the membrane of the tympa- 

 num. The pinna is a sheet of elastic cartilage covered 

 with skin, so folded as to direct the waves of sound 

 through the cartilaginous tube of the meatus, which is 

 continuous with it, to the membrane of the tympanum, or 

 eardrum, which closes the end of the passage. Along 



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