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STUDIES IN PHYSIOLOGY 



6. THE SENSE OF HEARING 



The External Ear. Attached to each side of the head is 

 an oval, more or less flattened expansion, composed largely 

 of cartilage and connective tissue. The irregular surface of 

 the outer portion of the ear doubtless helps somewhat, like 

 an ear trumpet, to converge the sound waves into the funnel - 



FIG. 142. Parts of the Eight Ear. 



Note. The coils of the cochlea (S) should project toward the observer. 

 A = auditory nerve and its branches. M = outer portion of ear. 

 B = semicircular canal. 

 G = tube of external ear. 

 I = utriculus. 

 I' = sacculus. 



P = middle ear with chain of bones. 



R Eustachian tube. 



S = cochlea. 



T = ear-drum or tympanum. 



like canal. This is about an inch long, and leads to the in- 

 terior of the head. In the lining of this canal are certain 

 wax glands ; these secrete a thin fluid which, on thicken- 

 ing, hardens into a yellow paste, the earwax. Across the 

 inner end of this tube of the external ear is stretched a 

 thin membranous partition, known as the eardrum, or tym'- 

 pa-num (Latin tympanum == drum). 



