STRUCTURE OF THE LARYNX. 
519 
681. To these arytenoid cartilages are attached two ligaments 
of elastic fibrous substance (§ 23), which pass forwards to he 
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 (l 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 (<?, 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 (y, 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, wdiich 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 
