138 



THE HUMAN BODY. 



voice-box ; but the lungs, the bronchial tubes, the trachea, 

 and the throat, mouth, and nose, all have a part in mak- 

 ing and forming sounds. 



2, The toy pipes, which have, near the mouth-piece, 

 narrow bands of brass, between which the air passes, and 



which make a reedy sound, are some- 

 what like the organ of voice. The 

 chest and lungs give the wind, the 

 trachea is the pipe, the larynx contains 

 the vocal cords, which make the sound. 

 The larynx is divided in two parts by 

 a membranous partition, which has a 

 slit in it, running forward and back- 

 ward. This slit may be opened or 

 shut, or made longer or shorter, by the 

 action of many little muscles, which 

 surround it. 



The edges of this slit, which is called 

 the glottis, are the vocal cords. Every 

 breath has to P ass through it; but, 

 in ordinary breathing, no sound is 

 produced. If we wish to make a sound, the little mus- 

 cles tighten up the cords, and make the slit narrow ; and, 

 as the lungs are squeezed in the chest, the air forced out 

 through the slit makes the cords vibrate. This makes 

 the sound. We shape this sound by changes in our 

 throats and mouths. 



3, A reed-organ is somewhat like the vocal apparatus ; 

 but, in the instrument, there is a pipe for every note. The 

 windpipe can be so varied in length and in size, and the 

 voice-box, with its cords, can be so changed in many ways, 

 that a single pipe can make many different sounds. 



Fig. 52. 



