PRODUCTION OF VOCAL SOUNDS. 481 



contraction, pulls together the upper parts of the arytenoid 

 cartilages between which it extends. 



The placing of the vocal cords in a position parallel one 

 with the other, is effected by a combined action of the various 

 little muscles which act on them the thyro-arytenoidei having, 

 without much reason, the credit of taking the largest share in 

 the production of this effect. Fig. 172 is intended to show the 

 various positions of the vocal cords under different circum- 

 stances. Thus, in ordinary tranquil breathing, the opening 

 of the glottis is wide and triangular, becoming a little wider 

 at each inspiration, and a little narrower at each expiration 

 (Fig. 172, see also p. 166). On making a rapid and deep 

 inspiration the opening of the glottis is widely dilated, as in 

 c, Fig. 172, and somewhat lozenge-shaped. At the moment 

 of the emission of sound, it is more narrowed, the margins of 

 the aryteuoid cartilages being brought into contact, and the 

 edges of the vocal cords approximated and made parallel, at 

 the same time that their tension is much increased. The 

 higher the note produced, the tenser do the cords become 

 (Fig. 172, A); and the range of a voice depends, of course, in 

 the main, on the extent to which the degree of tension of the 

 vocal cords can be thus altered. In the production of a high 

 note, the vocal cords are brought well within sight, so as to be 

 plainly visible with the help of the laryngoscope. In the ut- 

 terance of grave tones, on the other hand, the epiglottis is 

 depressed and brought over them, and the aryteuoid cartilages 

 look as if they were trying to hide themselves under it (Fig. 

 175). 



The epiglottis, by being somewhat pressed down so as to cover 

 the superior cavity of the larynx, serves to render the notes 

 deeper in tone, and at the same time somewhat duller, just as 

 covering the end of a short tube placed in front of caoutchouc 

 tongues lowers the tone. In no other respect does the epiglottis 

 appear to have any effect in modifying the vocal sounds. 



The degree of approximation of the vocal cords also usually 

 corresponds with the height of the note produced ; but probably 

 not always, for the width of the aperture has no essential in- 

 fluence on the height of the note, as long as the vocal cords 

 have the same tension ; only with a wide aperture, the tone is 

 more difficult to produce, and is less perfect, the rushing of the 

 air through the aperture being heard at the same time. 



No true vocal sound is produced at the posterior part of the 

 aperture of the glottis, that, viz., which is formed by the space 

 between the arytenoid cartilages, for, as Miiller's experi- 

 ments showed, if the arytenoid cartilages be approximated in 

 such a manner that their anterior processes tpucfy each other, 



