THE LARYNGEAL MOVEMENTS. 207 



cords, 7, are still further increased. When the action of the crico- 

 thyroid and posterior crico-arytenoid muscles ceases, the anterior 

 and posterior points of attachment of the vocal cords to the thyroid 

 and arytenoid cartilages, respectively, are drawn nearer to each other 

 by the lateral crico-arytenoid, c, and especially by the thyro-arytenoid 

 muscles, d ; thus the cords are relaxed, and they become, by virtue of 

 their elasticity, shorter. By some anatomists certain fibres of the 

 thyro-arytenoid muscles are described as entering or mixing with the 

 elastic tissue of the vocal cords ; and these muscles are believed by 

 them to be able thus to tighten the cords, even when they become 

 shortened. The lateral crico-arytenoids are, in that case, when acting 

 alone, said merely to shorten the vocal cords, without tightening them. 

 These two muscles may also act together. 



The narrowing of the glottis is effected by the single arytenoid 

 muscle, Fig. 56, b, which, passing across the middle line, draws the 

 arytenoid cartilages, *, together, and, in this manner, approximates 

 the vocal cords, or may even completely close the glottis. Besides 

 this, the lateral crico-arytenoid muscles, c, also narrow the glottis ; 

 for, by their contraction, they draw forward the lateral processes of 

 the arytenoid cartilages, and thus swing inwards their anterior pro- 

 cesses, approximate the vocal cords, and bring them into a state of 

 parallelism. 



With regard to the opening of the glottis, it may be observed that 

 each arytenoid cartilage is, as we have seen, Fig. 56, furnished with 

 an anterior projection for the attachment of the corresponding vocal 

 cord, 7, and with a lateral process for the insertion of the lateral, c, 

 and posterior, a, crico-arytenoid muscles; moreover, it is so articulated 

 on the upper surface of the cricoid cartilage, that besides being able 

 to move backwards and forwards, and from side to side, it can also per- 

 form a movement of rotation upon its vertical axis, that is to say, upon 

 an imaginary line passing through it from above. Hence, the outer 

 fibres of the posterior crico-arytenoid can pull the lateral processes of 

 the arytenoid cartilages backwards, swing their anterior processes out- 

 wards, and, in this manner, separate the vocal cords from each other 

 posteriorly, and so widen the glottis, especially behind. 



When, in tranquil breathing, the glottis is open and triangular, 

 only a soft sound is produced by the passage of the air through its 

 aperture ; the vocal cords are at rest, but still in a certain state of 

 tension, and not loose or relaxed ; during very rapid and powerful 

 expiration, however, a blowing or panting sound is audible, caused by 

 the friction of the air against the walls of the air-passages. The human 

 vocal apparatus is analogous to a wind instrument with a double mem- 

 branous tongue, the bronchi and trachea representing the wind-tube, 

 the vocal cords the double membranous tongue, and the parts above the 

 glottis the attached tube. For the production of vocal sounds, even 

 the feeblest, more air must pass through the glottis than in respira- 

 tion ; and this current of air must undergo periodic interruptions in its 

 passage through that fissure. The vocal cords, moreover, are made 

 more or less tense, and are approximated, so as to be parallel to each 

 other, and the fissure of the glottis is converted into a fine chink-like 



