166 



HUMAN BIOLOGY 

 VI. The Eak 



249. The external ear. — Attached to each side of the head is 

 an oval, more or less flattened expansion, composed largely of car- 

 tilage and connective tissue. The irregular surface of this outer 

 portion of the ear doubtless helps somewhat, like an ear trumpet, to 

 catch and .converge the sound waves into the funnel-like canal 

 which is about an inch long, and leads to the interior of the head. 



The Hammer 



The 

 Shell Tube 

 ICocKka). 



The Anvil. 



A. 



Eustachian Tube. 



Fig. 55. — Middle and inner ear, greatly enlarged. 



In the lining of this canal are certain wax glands; these secrete 

 a thin fluid which, on thickening, 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 (Fig. 55)). 



It is never safe for one to thrust into the canal of the ear any hard 

 object, because of the danger of puncturing the eardrum. Ordina- 

 rily the canal cleans itself, but if it is necessary to remove bits of 

 wax or dirt, this should be done with a tightly rolled corner of a piece 

 of cloth. It is dangerous, too, to punish a child by boxing the ears, 



