the Physiology of the Human Voice. 275 



vocal tube in which it is placed, the manner in which they are 

 adjusted to each other, and the acoustic effects resulting from 

 this reciprocal action, present an interesting field of inquiry. 



Although it has been demonstrated that the glottis is capa- 

 ble of producing all the range of tone without the aid of the 

 rest of the vocal organs, its function becomes more limited 

 when placed in the vocal tube, for in that position it can vi- 

 brate in perfection only when in unison with the pitch of the 

 tube. 



When the vocal tube has by any means lost its power of 

 vibrating in accordance with the glottis, the consequence is, that 

 the glottis will either merely reach phonation, produce dis- 

 cordant tones, or become silent altogether. 



Magendie mentions a person who having a small aperture 

 in the trachea, was obliged to tie a cravat tightly round it, to 

 restore the power of adjustment, and enable him to speak. 



I lately witnessed an analogous case of loss of voice owing 

 to a fistulous orifice below the glottis. 



The glottis being situated near the superior extremity of the 

 vocal tube, does not alter the fundamental pitch of the voice ; 

 hence Mr.Wheatstone* very justly remarks that the trachea 

 exerts the same influence below the glottis as it would above 

 itf. 



When the voice is raised in the scale from grave to acute, 

 a corresponding elevation takes place in the larynx, towards 

 the base of the cranium. 



By placing the finger on the pomum Adami, this motion 

 can be easily felt, and at the same time the thyroid cartilage 

 is drawn up within the os hyoides, and presses on the epi- 

 glottis ; the small space between the thyroid and the cricoid 

 closes X ; the pharynx is contracted ; the velum palati is de- 

 pressed and curved forwards ; the tonsils approach each other, 

 and the uvula is folded upon itself §. 



The reverse of these phsenomena takes place during the de- 

 scent of the voice. 



These are the principal phsenomena which can be recog- 

 nised by external observation ; the other changes being, on 

 account of their situation, invisible. 



* See Mayo's Physiology. 



+ Those physiologists who would assign to the thyroid ghind the mecha- 

 nical office of acting as a damper to stifle the reverberations of sounds in 

 the chest, must have very erroneous notions of the functions of the vocal 

 tube. 



: See fig. 7. 



§ Gerdy (Bulletin Universcl des Sciences,) remarks, " La luette se ra- 

 courcissegraducllement jusqu'ii s'efTaccr entierenient, lorsque lavoixmonte 

 tres-haut. ' Sec also Bcnnati, Rechcr. sur la Foi.r. 



2I2 



