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PHYSIOLOGY KOR nF.r.IXNKRS 



the broad part behind. The vocal cords are in this position 

 when they are at rest, that is, when ordinary respiration is 

 going on, but no voice is being produced. When voice is 

 being produced the arytenoids are drawn together, and so 

 the vocal cords become parallel, and the aperture between 

 them becomes merely a narrow slit. At the same time the 

 vocal cords are tightened by the crico-thyroid muscle increas- 

 ing the distance of the front of the thyroid from the arytenoids 



FIG. in. 



I. View of the human larynx from above as seen hy a small mirror held at the back 



of the mouth when light is reflected down the throat. A, condition when voice 

 is being produced, />, when no voice is being produced, e, epiglottis, cv, vocal 

 cords; ens, so-called false vocal cords, folds of mucous membrane lying above 

 the real vocal cords ; a, elevation caused by arytenoid cartilages ; s, in, elevations 

 caused by small cartilages connected with the arytenoids ; /, root of tongue. 



II. Diagrams of the glottis in the two conditions. 



in the manner already explained. By the stronger or weaker 

 action of these muscles, with the opposite effect produced by 

 the muscles which slacken the vocal cords (such as the thyro- 

 arytenoid muscles running parallel with them), the tension of 

 the vocal cords can be varied within wide limits. On this 

 depends the pitch of the note produced, when the cords are set 

 in vibration by a blast of expired air. A good singer can 



