ACTIONS OF THE LARYNGEAL MUSCLES. 611 



contraction they tend to pull together the outer angles 

 of the aryfcenoid cartilages in such a fashion as to rotate the 

 latter at their joint with the cricoid, and of course to throw 

 asunder their anterior angles to which the vocal cords are 

 attached. 



These posterior crieo-arytenoid muscles are opposed by 

 the crico-arytenoidei laterales, which, pulling in the opposite 

 direction from the other side of the axis of rotation, have 

 of course exactly the opposite effect, and close the glottis 

 (fig. 167, 4 and 5). 



The aperture of the glottis can be also contracted by 

 the arytenoid muscle (s, fig. 166, and 6, fig. 167), which, 

 in its 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-aryte- 

 noidei having, without much reason, the credit of taking 

 the largest share in the production of this effect. Fig. 165 

 is intended to show the various positions of the vocal cords 

 under different circumstances. 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. 165, see also p. 210). On 

 making a rapid and deep inspiration the opening of the 

 glottis is widely dilated, as in c, fig. 165, and somewhat 

 lozenge-shaped. At the moment of the emission of sound, 

 it is more narrowed, the margins of the arytenoid 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. 165, 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 



