504 HEARING, VOICE AND SPEECH 



With the exception of the crico-thyroid muscle which is innervated by the 

 superior and median laryngeals, the latter arising from the pharyngeal branch 

 of the vagus, the muscles of the larynx receive their nerve supply from the 

 recurrent laryngeal. 



2. VOICE PRODUCTION 



Production of sound in the larynx presupposes that the glottis is closed 

 and that the vocal cords are placed in a state of tension. If then air is 

 driven from the lungs under sufficient pressure, it forces its way through the 

 glottis and as it does so sets the vocal cords in vibration. 



Caginard-Latour and Griitzner have estimated the air pressure necessary 

 for this purpose. On patients with tracheal fistula? they connected a manome- 

 ter with the trachea by means of a tracheal cannula and demonstrated for 



FIG. 202. Laryngpscopic picture of the human throat, as seen during quiet inspiration. En- 

 larged twice (Heitzmann). 



a tone of medium height and strength a pressure of 140 to 40 mm. of water ; 

 for very loud tones, as in shouting at the top of the voice, a pressure as high 

 as 945 mm. of water was obtained. 



The power which produces this pressure comes from the muscles of expira- 

 tion, chiefly the abdominal muscles. It is said that good singers use only 

 the thoracic muscles of expiration. 



The sound produced in the larynx is modified as to its timbre but not as 

 to pitch, by the resonance chambers pharynx, mouth, nasal cavities, etc. 

 and the task of the voice culturist, besides that of inculcating correct habits 

 of breathing, consists merely in training the pupil to so shape these cavities 

 as to impart the most agreeable quality. 



3. REGISTERS OF VOICE 



Before the invention of the laryngoscope, our knowledge of the behavior 

 of the vocal cords, etc., in the production of voice was based mainly on 

 observations made with dissected preparations. But with the invention of 



