ACTION OF THE LARYNGEAL MUSCLES 



503 



Contraction of the cricothyroid increases the tension of the vocal cords by 

 rotating the cricoid cartilage upon the thyroid around an axis running through 

 the articulation which the small (lower) cornua of the thyroid make with the 

 cricoid. Thus the broad posterior plate of the cricoid to which the arytenoids 

 are attached is moved downward and backward, and, the arytenoids being 

 prevented by ligaments from slipping forward, as a consequence the vocal 

 cords are put on a stretch. 



The glottis is widened by moving the vocal processes of the arytenoid 

 cartilages, to which the vocal cords are attached, farther asunder. This is 

 accomplished chiefly by contractions of the posterior crico-arytenoid muscle 

 springing from the cricoid cartilage and attached to the muscular processes 

 of the arytenoid cartilages. The action of this muscle is represented schemat- 

 ically in Fig. 200. It contributes to the tension of the vocal cords by holding 

 the arytenoid cartilage against the muscles which tend to draw it forward 

 (Neuman). In this abducting action the posterior crico-arytenoid is aided 

 to some extent by the vertically directed portion of the lateral crico-arytenoid 

 (Ruhlmann). 



But for the most part the lateral crico-arytenoid is an adductor of the 

 vocal cords (Fig. 201) and the thyro-arytenoid lying over this muscle has 

 the same action. 



The vocalis or internal thyro-arytenoid muscle, regarded by several authors 

 as belonging to the thyro-arytenoid, runs from the angle of the thyroid car- 

 tilage to the arytenoid cartilage and is 

 applied to the outer margin of the vocal 

 cord of each side. It serves first to relax 



FIG. 200. Schematic representation of the 

 action of the posterior crico-arytenoid 

 muscles, after Testut. The red color 

 indicates the position of the vocal 

 cords and of the arytenoid cartilages, 

 when these muscles contract. 



FIG. 201. Schematic representation of 

 the action of the lateral crico-aryte- 

 noid muscle, after Testut. The red 

 color indicates the position of the vocal 

 cords and of the arytenoid cartilages 

 when these muscles contract. 



the vocal cords by approximating the points of their attachment. But a much 

 more important function is to impart the necessary internal tension and firm- 

 ness, as well as to give a favorable form and position to the whole mass of 

 the vocal cord, for intonation (Griitzner). 



