330 



THE HUMAN BODY. 



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

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

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

 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 Eustachian tube 

 (R, Fig. 95) pro- 

 ceeds and opens 

 into the pharynx. 

 This tube allows air 

 from the throat to 

 enter the tympanum, 

 and serves to keep 

 equal the atmospher- 



FIG. 96, The tympanic cavity and its bones, con- 

 siderably magnified. (?, the inner end of the ex- 

 ternal auditory meatus, closed internally by the 

 conical tympanic membrane; L, the malleus, or 

 hammer-bone; H, the incus, or anvil-bone; S, the 

 stapes, or stirrup-bone. 



ic pressure on each 

 side of 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 Eustachian tube? What is the use 

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

 is their function? 



