330 



THE HUMAN BODY. 



The External Ear consists of the expansion, M t seen on 

 the exterior of the head, called the concha, and a passage 

 leading in from it, the external auditory meatus, G. Thig 

 passage is closed at its inner end by the tympanic or drum 

 membrane, T. It is lined by a prolongation of the skin, 

 through which numerous small glands, secreting the wax 

 of the ear, open. 



The Tympanum, or drum chamber of the ear (Fig. 96 and 



P, Fig. 95), is an 

 irregular cavity in 

 the temporal bone, 

 closed externally by 

 the drum membrane. 

 From its inner side 

 the EustacMan tube 

 (R, Fig. 95) pro- 

 ceeds and opens 

 into the pharynx. 

 This tube allows air 

 fsom the throat to 

 enter the tympanum, 

 and serves to keep 



FIG. 96. The tympanic cavity and its bones, con- pnivil f] 1P nfmrxsnTipr 



siderably magnified. G, the inner end of the ex- U i Utl 



ternal auditory meatus, closed internally by the \ n -nvnccnvn rm oor"U 



conical tympanic membrane: I/, the malleus, or 1 



hammer-bone; H, the incus, or anvil-bone; S, the -i^ r & L-I n ,q w 



stapes, or stirrup-bone. Side 01 the drum 



membrane. Three small bones (Fig. 96) stretch across 

 the tympanic cavity from the drum membrane to the laby- 

 rinth ; they transmit the vibrations .of the membrane, 

 produced by sound-waves ,in the air, to the liquid of the 



Describe the external ear. 



What is the tympanum? The Eustaehian tube? What is the use 

 of the Eustaehian tube? What bones lie in the tympanum? What 

 is their function? 



