ORGANS OF HEARING AND OF THE VOICE. 203 



stretched across like harp-strings, constitute the lyra. The separate uses of 

 these various parts are not yet fully known. The membrane of the tym- 

 panum may be pierced, and the chain of bones may be broken, -nithout en- 

 tire loss of hearing. 



438. In the hearing apparatus of the lower orders of 

 cuUarittes ^of animals, all the parts belonging to the human ear do not 

 the hearing ap- exist. In fishes, the ear consists only of the labyrinth; and 

 LweranimsJ^? "^ lower animals the ear is simply a Uttle membranous 

 cavity fiUed with fluid in which the fibres of the nerves of 

 hearing float. 



439. All persons can not hear sounds alike, 

 ^on" "^^ hZr In different individuals the sensibility of the 

 Bound alike? auditorj nerves varies greatly. 



440. The whole ranire of human hearing, 



VThat is the „ , ^ t> . i i • i 



range of hn- from the lowcst uotc 01 the organ to the high- 

 est known cry of insects, as of the cricket, in- 

 cludes about nine octaves. 

 „ 441. In the human svstem, the parts con- 



What are the •• • i ^ • " r i i 



organs of ccmcd m the production ot speech and music, 



voice? . . 



are three : the wind-pipe, the larynx, and 

 the glottis. 



What ia the ^42. The Wind-pipe is a tube extending 

 wiud-pipc? £j.Qj^^ Qjjg extremity of the throat to the other, 

 which terminates in the lungs, through which the air 

 passes to and from these organs of respiration. 

 What is the ^•^- The Larynx, which is essentially the 

 Laryni? Qrgau of spcecli, is an enlargement of the up- 

 per part of the wind-pipe. The Larynx terminates in 

 two lateral membranes which approach near to each other, 

 having a little narrow opening between them called the 

 glottis. The edges of these membranes form what is 

 called the vocal chords. 



How is voice '^^- III order to produce sound, the air ex- 

 produced? pired from the lungs passes through the wind- 

 pipe and out at the larynx, through the opening between 

 the membranes, the glottis : the vibration of the edges of 

 these membranes, caused by the passage of air, produces 

 sound. 



