754 



VOICE AND SPEECH 



[OIL LV. 



verge upwards and outwards, and are inserted into the outer angle of the base of the 

 arytenoid cartilage behind the attachment of the lateral crico-arytenoid muscle. 

 Near their insertion the upper fibres are blended with the lower fibres of the ary- 

 tenoid muscle. 



These muscles draw the outer angles of the arytenoid cartilages backwards and 

 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. Its upper part is more or less 

 blended with the thyro-arytenoid, and a few of its fibres are continuous round the 

 outer side of the arytenoid cartilage with the arytenoid muscle. 



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 



Lig. ary-epiglott. 



Cart. Wrisbergii 

 Cart. Santorini 



mm. Aryten. obliqu. 



Crico-arytenoid. post. 



Cornu inferior 

 Lig. cerato-cric. 



Pars post. inf. membrani j 



Pars cartilag. 



Fio. 555. The larynx as seen from behind. To show the 

 intrinsic muscles posteriorly. (Stoerk.) 



