THE RESPIRATORY SYSTEM. 69 



The chief organ of the voice is the larynx. 



This is really an expansion of the upper 



The larynx. , . . , , .. 



end of the wind-pipe, as already seen. 

 The prominent point on the front of the neck, com- 

 monly called "Adam's apple," is a part of the larynx. 

 The cartilages of which the larynx is mainly composed 

 form a sort of box, along whose two inner sides are 

 stretched two membranous chords called the vocal 

 chords. These come more or less closely together at 

 the middle of the larynx, the slit or chink between 

 them being called the glottis. Through this glottis 

 every in-going and out-going breath ordinarily passes 

 silently. But when the muscles which regulate the 

 vocal chords tighten up these chords, while air is 

 being expelled from the lungs, a sound is produced, 

 either high or low, according to the degree of ten- 

 sion, or tightness, to which the vocal chords are drawn. 

 If you have learned to sing up and 

 down the eight tones of the musical 

 scale, you may easily perform an experi- 

 ment on the action of the muscles which control the 

 tension of the vocal chords. Sound slowly the sylla- 

 bles up and down the scale. You will feel a change 

 in the contraction of the larynx muscles at every 

 change of tone. Going up the scale, that is, to a 

 higher and higher pitch, you will feel a tightening 

 action of these muscles: coming down the scale to a 

 lower and lower pitch, an opposite effect will be felt. 

 The action of the breath on the vocal 

 chords which has just been described, 



An Experi- 

 ment. 



