THE LARYNX 345 



is strengthened posteriorly by a strong band which restricts 

 movement of the arytaenoid cartilage. 



Cartilagines Cuneiformes. The cuneiform cartilages are 

 two little rod-shaped nodules of yellow elastic cartilage, which 

 are placed one in each ary-epiglottic fold near its posterior 

 end (Fig. 120). They are not always present. 



Actions of the Laryngeal Muscles. The dissector should 

 now consider the manner in which the muscles of the larynx 

 operate upon the vocal folds, in the production of the voice. 

 Tension of the vocal folds is produced by the contraction of 

 the crico-thyreoid muscles. The straight parts of the muscles 

 pull the upper border of the cricoid cartilage upwards, whilst 

 the oblique portions, through their insertions into the inferior 

 cornua, draw the cricoid cartilage backwards, thereby increas- 

 ing the distance between the angle of the thyreoid cartilage 

 and the vocal processes of the arytoenoid cartilages. When 

 the" crico-thyreoid muscles cease to contract, the relaxation of 

 the vocal folds is brought about by the elasticity of the 

 ligaments. The vocalis and the thyreo-arytaenoideus 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 vocal folds, 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 arytae- 

 noid^us muscle, which draws together the arytaenoid carti- 

 lages. The lateral and posterior crico-arytaenoid muscles 

 also modify the width of the rima glottidis. When they act 

 together they assist the arytaenoid muscle in closing the rima 

 glottidis, but when they act independently they are antago- 

 nistic muscles. Thus the crico-arytanoidei posteriores, by draw- 

 ing the muscular processes of the arytaenoid cartilages back- 

 wards and laterally, swing the processus vocales and the vocal 

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

 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, 



