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CONTRIBUTIONS TO ZOOLOGICAL PATHOLOGY. 
The thyro-arytenoidei anteriores et posteriores are the special 
muscles that produce oblique inversion of the arytenoid cartilages, 
and thus carrying them towards the central line of the laryngeal 
cavity, tend to relax the vocal chords and close the rima glottidis. 
Associated with them in this function are the arytenoidei, which, 
by approximating the cartilages superiorly, firmly and securely 
shut this important isthmus of the air passages. 
The thyro-arytenoidei transversi, on the other hand, produce 
oblique eversion of the apices of the arytenoid cartilages and their 
cuneiform appendages, and thus they increase the size of the rima 
glottidis and render tense the vocal chords. 
The aryteno-epiglottidei muscles have a double function to per- 
form. When taking their fixed points above, at the arytenoid 
cartilages, they will tend to depress the epiglottis on the anterior 
aperture of the larynx ; if below, at the epiglottis, they will invert 
the arytenoids, and tend to relax the vocal chords ; but if both 
ends of the muscles be fixed, they will then compress the external 
parietes of the laryngeal ventricles, and empty them of their 
mucous or other accidentally acquired contents into the general 
cavity of the larynx, where such matters will be carried forwards 
into the nose or mouth by the instinctively forced expiration or 
cough that is always and instantly induced by any irritation being 
excited in this very sensitive membrane. The hyo-epiglottidei 
will only act in elevating and bracing, upwards and forwards, the 
epiglottis to the base of the tongue. 
Excluding, therefore, the thyro-hyoidei, the aryteno-epiglottidei, 
and the hyo-epiglottidei muscles, as possessing trifling influence 
over the movements of the arytenoid cartilages, and the indirect 
conditions of the vocal chords and rima glottidis, the remaining 
seven pairs of muscles may be arranged under two groups, viz. the 
C Crico-thyroidei 
Muscles opening rima glottidis < Crico-arytenoidei superiores 
( Thyro-arytenoidei transversi. 
( Thyro-arytenoidei superiores 
, , . • ) Thyro-arytenoidei inferiores 
Muscles closing rima glottidis + Ar ^ eno -j ei 
( Crico-arytenoidei inferiores. 
It will thus be seen that those muscles that produce oblique in- 
version of the arytenoid cartilage, and consequent diminution in 
the size of the rima glottidis, are apparently more numerous than 
those that produce the opposite conditions of these structures ; but 
when we come to observe the great influence which the position of 
the thyroid cartilage indirectly possesses over the state of the rima 
glottidis, and the very considerable power exerted over the carti- 
