THE TONGUE 429 



nodules of yellow elastic cartilage, which are placed one in 

 each ary<-epiglottic fold near its posterior end. They are not 

 always present. 



Action of the Laryngeal Muscles. The dissector should now consider 

 the manner in which the muscles of the larynx operate upon the vocal 

 ligaments in the production of the voice. Tension of the vocal cords is pro- 

 duced by the contraction of the crico-thyreoid muscles. The oblique parts 

 of the muscles pull the upper border of the cricoid cartilage upwards, 

 whilst the straight portions, through their insertions into the inferior cornua, 

 draw the cricoid cartilage posteriorly, thereby increasing the distance 

 between the angle of the thyreoid cartilage and the vocal processes of the 

 arytasnoid cartilages. When the crico-thyreoid muscles cease to contract, 

 the relaxation of the cords is brought about by the elasticity of the 

 ligaments. The vocalis and the thyreo-arytsenoideus must be regarded 

 as antagonistic to the crico-thyreoid muscles. When they contract they 

 approximate the angle of the thyreoid cartilage to the arytsenoid cartilages, 

 and still further relax the cords, and when they cease to act, the elastic 

 ligaments of the larynx again bring about a state of equilibrium. 



The width of the rima glottidis is regulated by the arytsenoideus muscle, 

 which draws together the arytsenoid cartilages. The lateral and posterior 

 crico-arytsenoid muscles also modify the width of the rima glottidis. When 

 they act together they assist the arytsenoid muscle in closing the glottis, 

 but when they act independently they are antagonistic muscles. Thus the 

 crico-arytcenoidei posteriores, by drawing the muscular processes of the 

 arytsenoid cartilages postero-laterally, swing the processus vocales and the 

 vocal folds laterally, and thus open the rima. The crico-arytcenoidei 

 laterales act in exactly the opposite manner. By drawing the muscular 

 processes in an opposite direction they close the rima. 



But the muscles of the larynx have another function to perform besides 

 that of vocalisation. It was formerly thought that the superior aperture 

 of the larynx was closed, during deglutition, by the folding back of the 

 epiglottis ; that in fact the epiglottis, during the passage of the bolus of 

 food, was applied like a lid over the entrance to the vestibule of the larynx. 

 The investigations of Prof. Anderson Stuart have shown that the superior 

 aperture of the larynx is closed during swallowing by the close apposition 

 and the forward projection of the two arytsenoid cartilages, which are 

 forced against the tubercle of the epiglottis. The muscles chiefly concerned 

 in this movement are the thyreo- arytsenoid muscles and the transverse 

 arytoenoid muscle. These muscles form a true sphincter vestibuli. The 

 ary-epiglotticus muscle also assists in the closure. 



THE TONGUE. 



The tongue is a muscular organ placed on the floor of 

 the mouth. It has important duties to perform in connection 

 with the functions of mastication, deglutition, and articulation. 

 Moreover, the mucous membrane which covers it is specially 

 modified, in certain localities, in connection with the peripheral 

 terminations of the nerves of taste. The root of the tongue 

 is attached to the hyoid bone ; the pointed anterior extremity 



