THE VOICE 229 



These muscles, when they contract, put the 

 vocal cords on the stretch, and the stretch 

 increases as the pitch of the note rises. If we 

 remember that the true vocal cords pass 

 forward from the arytenoids to the thyroid, and 

 if we suppose that each arytenoid is capable of 

 rotating round a vertical axis passing from the 

 apex of the pyramid to its base, we can under- 

 stand how the glottis is opened and closed. Two 

 small muscles, the posterior crico- arytenoids^ 

 pass from the signet of the cricoid to the outer 

 angles of the base of the arytenoids, and when 

 they contract they so rotate the arytenoids 

 as to carry outwards the cords and thus they 

 enlarge the aperture of the glottis. Their 

 antagonists are a pair of small muscles, the 

 lateral crico- arytenoids, which pass backwards 

 from the sides of the cricoid to the outer 

 angles of the arytenoids. When these con- 

 tract they pull the angle forwards and inwards, 

 and thus approximate the cords. By these 

 simple mechanisms the position and tension of 

 the cords is controlled. The amplitude of 

 movement of each muscle is only a very 

 small fraction of an inch, and yet a soprano 



