146 



PHYSIOLOGY 



CHAP. 



preceded by closure of the whole glottis, or of the pars mem- 

 branacea (Fig. 98). 1 Now the emission of tones coincides with 

 the rapid opening and vibration of the vocal cords by the blast of 

 air forced through the glottis by the expiratory muscles. The 

 vibrations of the cords are not limited to their narrow margins, 

 but extend more or less through their entire mass. At the same 

 moment the epiglottis is somewhat raised, particularly in high 

 notes ; the aryteno-epiglottidean folds are stretched ; and the false 

 vocal cords are drawn slightly nearer together and stretched, but 

 they do not vibrate. At the same moment the whole larynx 

 becomes more or less firmly fixed by the action of the extrinsic 

 muscles (thyro-hyoid, sterno-thyroid, pharyngeal, etc.), and rises 

 with the emission of the high notes, and falls with the low notes. 

 During the production of high notes the tongue contracts 

 energetically, the tip being drawn back, and the base lifted. The 

 soft palate is raised towards the posterior wall of the pharynx, 



FIG. '.is. Positions of glottis previous to production of the voice. 



and the pillars of the fauces approximate and narrow its opening. 

 In deep notes, on the contrary, the tongue contracts slightly and 

 remains flat ; the soft palate is raised, and the pillars of the fauces 

 move apart. But the most important of all these changes in the 

 voice-producing apparatus are the vibration of the vocal cords 

 and the form of the membranous glottis, which varies considerably 

 with the pitch, intensity, and register of the voice. 



In order that the vocal cords should vibrate, it is necessary 

 for the air- current passing through them to be at a certain 

 pressure, sufficient to displace them from their position of 

 equilibrium. In a case of tracheal fistula in a woman, Cagnard- 

 Latour, by fitting a manometer into the mouth of the fistula, was 

 able to measure the pressure of the blast of air during the 

 production of sounds of different pitch. He found a pressure of 

 160 mm. H 2 necessary for sounds of medium pitch, of 200 mm. 

 for high, and of 945 mm. for the highest notes. Griitzner 

 obtained approximately the same figures in a young man on 

 whom tracheotomy had been performed. 



Adduction of the vocal cords and narrowing of the glottis 



1 This is not in agreement with some later observations. F. A. W. 



