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LARYNGEAL MUSCLES. 921 
inferior cornua, draw the thyroid cartilage forwards, thereby increasing the distance 
between the angle of the thyroid cartilage and the vocal processes of the arytenoid car- 
tilages. W hen the erico- thy roid muscles cease to contract, the relaxation of the cords is 
brought about by the elasticity of the igaments. The thyro-arytenoid muscles must be 
regarded as antagonistic to the crico-thyroid muscles. When they contract they approxi- 
mate the angle of the thyroid cartilage to the arytenoid cartilages, and still further relax 
the true yoeal cords; and when they cease to act the elasticity of the hgaments 
of the larynx again restore the state of equilibrium. The ary-vocales muscles, 
by the insertion of their fibres into the true vocal cords, may tighten portions of these 
cords, whilst they relax at the same time the parts behind. 
The width of the rima glottidis is regulated by the arytenoideus muscle, which draws 
together the two arytenoid cartilages, and this may be done so effectually that the inner 
surfaces of these cartilages come into contact; the glottis respiratoria is thus com- 
pletely closed. ‘The lateral and posterior crico-arytenoid muscles also modify the width 
of the rima glottidis. When they act together they assist the arytenoideus muscle in 
closing the glottis, but when they act independently they are antagonistic muscles. ‘Thus 
the posterior crico-arytenoid muscles, by drawing the muscular processes of the arytenoid 
cartilages outwards and backwards, swing the processus vocales and the vocal cords out- 
wards, and thereby open the rima. The lateral erico- -arytenoid muscles act in exactly the 
Opposite manner. By drawing the muscular processes of the arytenoid cartilages for wards 
and inwards, they approximate the processus vocales and close the rima. 
Closure of the Larynx during Deglutition.— But the muscles of the larynx 
have another function to perform besides vocalisation and regulating the amount of air 
passing to and fro through the glottis. During deglutition it is requisite that the com- 
munication between the pharynx and larynx should be closed, so as to prevent the 
fluid or solid parts of the food entering the respiratory passages. Formerly it was believed 
that this was effected by the folding back of the epiglottis ; that in fact the epiglottis, dur- 
ing the passage of the food, is applied like a lid over the entrance into the vestibule of the 
lary nx. The observations ‘of Professor Anderson Stuart would seem to indicate that this 
view is incorrect. According to Professor Stuart it is not the anterior wall of the vestibule 
which moves; the epiglottis stands erect, whilst the posterior wall formed by the 
arytenoids is carried forwards. In the process of closing the laryngeal entrance the aryte- 
noid cartilages are closely approximated, glide forwards, Sat are then inclined towards the 
epiglottis. “The result of this is that the “laryngeal opening is converted into a T-shaped 
fissure. The mesial limb of the T is formed by the interval between the closely-applied 
arytenoid cartilages, whilst the cross limb, which lies in front, is bounded anteriorly by the 
epiglottis and behind by the aryteno-epiglottidean folds. The apices of the arytenoid 
cartilages, with the cartilages of Santorini, are pressed against the cushion of the epiglottis, 
whilst the lateral margins ‘of the epiglottis are pulled backwards so as to make the trans- 
verse limb of the fissure distinctly concave in a backward direction. |The muscles chiefly 
concerned in producing these movements are the external thyro-arytenoid and the trans- 
verse arytenoid muscles. These form a true sphincter vestibuli. The thyro-ary-epiglotti- 
dean muscles also come into play. They pull upon the epiglottis so as to produce tight 
application of its cushion to the ar ytenoid cartilages and the cartilages of Santorini, and 
they also curve its margins backwards so as to increase its posterior concavity. 
Vessels and Nerves of the Larynx.—Two branches of the vagus nerve, viz. the superior 
laryngeal and the recurrent laryngeal nerves, supply the larynx. The superior laryngeal divides 
into the internal and external laryngeal branches. The external laryngeal nerve supplies the 
crico-thyroid muscle; whilst the internal laryngeal nerve enters the larynx by piercing the 
lateral part of the thyro-hyoid membrane to supply the laryngeal mucous membrane. The re- 
current laryngeal nerve reaches the larynx from below, and supplies all the intrinsic laryngeal 
muscles with the exception of the crico-thyroid. 
The superior laryngeal artery, a branch of the superior thyroid, accompanies the internal 
laryngeal nerve ; whilst the inferior laryngeal artery, which springs from the inferior thyroid, 
accompanies the recurrent laryngeal nerve. These two vessels ramify in the laryngeal wall and 
supply the mucous membrane, the glands, and muscles. 
Growth-Alterations, and Sexual Differences in the Larynx.—A considerable 
amount of variation may be noticed in the size of the larynx in different individuals. 
This is quite independent of stature, and explains to a great extent the difference in the 
pitch of the voice which is observable in different persons. But quite apart from these 
individual variations, there is a marked sexual difference in the size of the larynx. The 
male larynx is not only absolutely but also relatively larger than the female larynx. This 
is noticeable in all its diameters, but more particularly in the antero-posterior diameter, 
