VOICE AND SPEECH. 231 



VOICE AND SPEECH. 



The larynx is the organ of voice. Speech is a modification of voice, and 

 is produced by the teeth and the muscles of the lips and tongue, coordinated 

 in their action by stimuli derived from the cerebrum. 



The structures entering into the formation of the larynx are mainly the 

 thyroid, cricoid, and arytenoid cartilages; they are so situated and united by 

 means of ligaments and muscles as to form a firm cartilaginous box. The 

 larynx is covered externally by fibrous tissue, and lined internally with mu- 

 cous membrane. 



The vocal bands are four ligamentous bands,running anteroposteriorly 

 across the upper portion of the larynx, and are divided into the two superior 

 or false vocal bands, and the two inferior or true vocal bands; they are attached 

 anteriorly to the receding angle of the thyroid cartilages, and posteriorly to 

 the anterior part of the base of the arytenoid cartilages. The space between 

 the true vocal bands is the rima glottidis. 



The muscles which have a direct action upon the movements of the vocal 

 bands are nine in number, and take their names from their points of origin and 

 insertion viz., the two crico-thyroid, two thyro-arytenoid, two posterior 

 crico-arytenoid, two lateral crico-arytenoid, and one arytenoid muscles. 



The crico-thyroid muscles, by their contraction, render the vocal bands 

 more tense by drawing down the anterior portion of the thyroid cartilage 

 and approximating it to the cricoid, and at the same time tilting the posterior 

 portion of the cricoid and arytenoid cartilages backward. 



The thyro-arytenoid, by their contraction, relax the vocal bands by drawing 

 the arytenoid cartilage forward and the thyroid backward. 



The posterior crico-arytenoid muscles, by their contraction, rotate the ary- 

 tenoid cartilages outward and thus separate the vocal bands and enlarge the 

 aperture of the glottis. They principally aid the respiratory movements 

 during inspiration. 



The lateral crico-arytenoid muscles are antagonistic to the former, and by 

 their contraction rotate the arytenoid cartilages so as to approximate the 

 vocal bands and constrict the glottis. 



The arytenoid muscle assists in the closure of the aperture of the glottis. 



The inferior laryngeal nerve animates all the muscles of the larynx, with 

 the exception of the crico-thyroid. 



Movements of the Vocal Bands. During respiration the movements of 

 the vocal bands differ from those occurring during the production of voice. 



At each inspiration the true vocal bands are widely separated, and the aper- 

 ture of the glottis is enlarged by the action of the crico-arytenoid muscles, 

 which rotate outward the anterior angle of the base of the arytenoid cartilages; 



