STRUCTUEE OF THE LARYNX. 519 



681. To these arytenoid cartilages are attached two ligaments 

 of elastic fibrous substance ( 23), which pass forwards to be 

 attached to the front of the thyroid cartilage, where they meet 

 in the same point. These are the instruments concerned in the 

 production of sound, and also in the regulation of the aperture 

 by which air passes into the trachea; and they are termed 

 the vocal cords or ligaments (fig. 263, li). By the meeting of 

 these ligaments in front and their separation behind, the usual 

 aperture has the form of a V ; but it may be narrowed by the 

 drawing-together of the arytenoid cartilages, until the two 

 vocal ligaments touch each other along their whole length, 

 and the aperture is completely closed. In this manner, the 

 amount of air permitted to pass through the larynx is regu- 

 lated ; and a protection is afforded against the entrance of 

 solid substances. An additional guard is afforded by the 

 doubling of the lining membrane, in such a manner as to form 

 a second pair of folds (I s, fig. 263), above the preceding ; and 

 over the space between these (which is much wider than that 

 between the vocal cords) there is a valve-like flap, the epi- 

 glottis (e, fig. 262), which is pushed-down upon it in the act 

 of swallowing, so as to prevent the entrance of solid or fluid 

 particles into the space beneath, which is called the glottis. 

 From the causes formerly mentioned ( 193), such particles 

 are occasionally drawn into the glottis ; and they excite, by a 

 reflex action, an involuntary and extremely violent cough, 

 which tends to expel them again. Sometimes, however, solid 

 bodies of no inconsiderable size find a lodgment in the wide 

 spaces (v, fig. 263) between the upper and lower pair of liga- 

 ments, which are termed the ventricles of the larynx ; and 

 occasionally they pass through the opening between the vocal 

 cords, which is termed the rima glottidis or fissure of the 

 glottis, into the wind-pipe. 



682. In the ordinary acts of inspiration and expiration, the 

 arytenoid cartilages are wide apart, so that the aperture is as 

 large as possible ; but for the production of vocal sounds, it 

 is necessary that the aperture should be narrowed, and that 

 the flat sides, rather than the edges, of the vocal ligaments 

 should be opposed to one another. This is accomplished by 

 a peculiar movement of the arytenoid cartilages, occasioned 

 by the contraction of certain muscles. When these ligaments 

 are thus brought into position, the air in passing through the 



