6o8 VOICE AND SPEECH. 



can be made the means not only of closing the larynx 

 against the entrance and exit of air to or from the lungs, 

 but also can be stretched or relaxed, shortened or length- 

 ened, In accordance with the conditions that may be 

 necessary for the air in passing over them, to set them 

 vibrating and produce various sounds. Their action in 

 respiration has been already referred to (p. 210), in con- 

 nection with ordinary tranquil respiration, and also (p. 233, 

 et seq,} with other respiratory acts, in which the opening 

 or closing of the glottis, or, in other words, the close 

 apposition or separation of the vocal cords, is an essential 

 part of the performance. In these respiratory acts, how- 

 ever, any sound that may be produced, as in coughing, 

 is, so to speak, an accident, and not performed with 

 purpose. In the present chapter the sound produced by 

 the vibration of the vocal cords is the only part of their 

 function with which we have to deal. 



It will be well, perhaps, to refer to a few points in the 

 anatomy of the larynx, before considering its physiology 

 in connection with voice and speech. 



The principal parts entering into the formation of the 

 larynx (figs. 161 and 162) are (t) the thyroid cartilage ; 

 (c) the cricoid cartilage ; (a) the two arytenoid cartilages ; 

 and the two true vocal cords (A, cv, fig. 165). The 

 epiglottis (fig. 162, e) has but little to do with the voice, 

 and is chiefly useful in falling down as a ' lid ' over the 

 upper part of the larynx, to prevent the entrance of 

 food and drink in deglutition. The false vocal cords 

 (cvs, fig. 165), and the ventricle of the larynx, which is 

 a space between the false^ and the true cord of either side, 

 need be here only referred to. 



The thyroid cartilage (fig. 163, i to 4) does not form a 

 complete ring around the larynx, but only covers the front 

 portion. The cricoid cartilage (fig. 163, 5, 6), on the other 

 hand, is a complete ring ; the back part of the ring being 

 much broader than the front. On the top of this broad por- 

 tion of the cricoid are the arytenoid cartilages (fig. 162, a) 



