802 



VOICE AND SPEECH 



[CH. LVII. 



inwards, and thus rotate the anterior or vocal processes outwards, and widen the 

 rima glottidis. They come into action during deep inspiration. If they are paralysed, 

 the lips of the glottis approach the middle line and come in contact during each 

 inspiration, so that dyspnoea is produced. 



3. Lateral crico-arytenoid. This arises from the sloping upper border of the 

 cricoid cartilage, and is inserted into the muscular process of the arytenoid carti- 

 lage, and the adjacent part of its anterior surface. 



These muscles draw the muscular processes of the arytenoid cartilages forwards 



and downwards, and thus ap- 

 proximate the vocal cords. They 

 are antagonistic to the posterior 

 crico-arytenoids. 



4. Thyro - arytenoid. This 

 consists of two portions, inner 

 and outer. The inner portion 

 arises in the lower half of the 

 angle formed by the alae of the 

 thyroid cartilage, and passing 

 backwards is attached behind to 

 the vocal process and to the ad- 

 jacent parts of the outer surface 

 of the arytenoid cartilage. These 

 fibres are joined internally by 

 short fibres which are attached 

 in front to the vocal cord, and 

 behind to the vocal process. 

 Some oblique fibres pass from 

 the sloping portion of the crico- 

 thyroid membrane below the 

 vocal cord, upwards, outwards, 

 and somewhat backwards, to 

 end in the tissue of the false 

 vocal cord. The fibres of the 

 outer portion arise in front from 

 the thyroid cartilage close to the 

 origin of the inner portion and from the crico-thyroid membrane. They pass back- 

 wards to be inserted in part into the lateral border and muscular process of the 

 arytenoid cartilage, and in part they pass obliquely upwards towards the aryteno- 

 epiglottidean fold, ending in the false vocal cord. The portion of this muscle which 

 extends towards the epiglottis is often described as a separate muscle (thyro- 

 epiglottidean) ; it resembles the crico-arytenoid in that some of its fibres are con- 

 tinuous with those of the arytenoid muscle. 



The antero-posterior fibres will tend to draw forward the arytenoid cartilage, 

 and with it the posterior part of the cricoid cartilage, rotating the latter upwards 

 and antagonising the action of the crico-thyroid muscle, the effect being to relax the 

 vocal cords. But if the latter are kept stretched those fibres of the inner portion of 

 the muscle which are inserted into the vocal cord may serve to modify its elasticity, 

 tightening the parts of the cord in front of, and relaxing those behind, its attach- 

 ment. The vertical fibres of the muscle which extend from the crico-thyroid mem- 

 brane across the base of the vocal fold and over the ventricle into the false vocal 

 cord, render the free edge of the former more prominent. Then the fibres which are 

 inserted into the muscular process and outer surface of the arytenoid cartilage will 

 tend to draw the arytenoid cartilage forwards and rotate it inwards ; finally, the fibres 

 which pass into the aryteno-epiglottidean fold may assist in depressing the epiglottis. 

 If these muscles are paralysed, the lips of the glottis are no longer parallel, but 

 are curved with the concavity inwards, and a much stronger blast of air is required 

 for the production of the voice. 



5. Arytenoid. When the mucous membrane is removed from the back of the 

 arytenoid cartilages, a band of transverse fibres is exposed, on the dorsal surface of 

 which are two slender decussating oblique bundles. These are often described as 



Lig. ary-epiglott. 



Cart. Wrisbergii - 

 Cart. Santorini 



mm Aryten. obliqu. 



Crico-arytenoid. post. 



Cornu inferior 



Lig. cerato-cric. 



Pars post. inf. membrani 



Pars cartilag 



FIG. 502. The larynx as seen from behind. To show the 

 intrinsic muscles posteriorly. (Stoerk.) 



