PHONATION; ARTICULATE SPEECH. 



625 



The thyro-arytenoid muscle arises from the inferior two-thirds of the 

 inner surface of the thyroid cartilage just external to the median line. From 

 this origin the fibers pass backward and outward, to be inserted into the 

 anterior surface and external angle of the arytenoid cartilage. The inner 

 portion of the muscle lies close to and supports, if it does not constitute a part 

 of, the vocal band. The action of the thyro-arytenoid muscle in conjunction 

 with the lateral crico-arytenoid is to rotate the arytenoid cartilage around the 

 vertical axis and to draw the vocal process forward and inward, thus carry- 

 ing the vocal cord toward the median line. When the muscles of the two 

 sides simultaneously contract, the vocal bands are closely approximated 

 and the space between them, the rima vocalis, reduced to a mere slit, one 

 of the conditions essential to phonation (Fig. 291). 



The arytenoid muscle consists (i) of transversely arranged fibers which 

 arise from and are inserted into the outer surface of the opposite arytenoid 



FIG. 290. GLOTTIS WIDELY OPENED 

 FROM SIMULTANEOUS CONTRACTION OF 

 BOTH CRICO-ARYTENOID MUSCLES, b. 

 Epiglottis, rs. False vocal band. ri. 

 True vocal band. ar. Arytenoid car- 

 tilages, a. Space between the arytenoids. 

 c. Cuneiform cartilages, ir. Interarytenoid 

 fold. rap. Aryepiglottic fold. cr. Car- 

 tilage rings. (Mandl.) 



FIG. 291. POSITION OF THE VOCAL 

 BANDS DUE TO THE SIMULTANEOUS 

 CONTRACTION OF BOTH LATERAL CRICO- 

 ARYTENOID MUSCLES AND BOTH THYRO- 

 ARYTENOID MUSCLES, b. Epiglottis, rs. 

 False vocal band. ri. True vocal band. 

 or. Space between the arytenoid cartil- 

 ages, the glottis respiratoria. ar. Ary- 

 tenoid cartilages, c. Cuneiform carti- 

 lages, rap. Aryepiglottic fold. ir. In- 

 terarytenoid fold. (Mandl.) 



cartilages, and (2) of obliquely directed fibers which arise from the outer 

 angle of one arytenoid to be inserted into the apex of the other. In their 

 course they decussate in the median line. The action of this muscle is to 

 approximate the arytenoid cartilages and thus obliterate that portion of the 

 glottis between the vocal processes, the rima respiratoria, and so direct the 

 expiratory blast of air toward and through the rima vocalis. 



The collective actions of the three foregoing muscles is to close or con- 

 strict the glottis, and for this reason they are spoken of as the adductor or 

 phonatory muscles. 



The crico-thyroid muscle arises from the side and front of the cricoid 

 cartilage and is inserted above into the lower border of the thyroid cartilage. 

 The action of this muscle is to draw up the anterior part of the cricoid car- 

 tilage toward the thyroid, which remains stationary, and to swing the 

 quadrate plate of the cricoid and the arytenoid cartilages downward and 

 backward. This movement has the result of tensing the vocal bands. 

 The cricoid is at the same time drawn backward by the action of the more 

 longitudinally disposed fibers. 

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