138 



PHYSIOLOGY 



CHAP. 



the arytenoids, where they cross in the median line, and then 

 run along in the aryteno-epiglottidean fold to be inserted in 

 the base of the epiglottis. The two latter start from the lower 

 part of the internal angle of the thyroid, and turn backwards 

 and upwards to the muscular processes of the arytenoid. The 

 chief function of these muscles is to constrict the glottis, and 

 reinforce the transverse arytenoid muscle. 



The lateral crico-arytenoid muscle also aids in the abduction 

 of the vocal cords. This muscle runs obliquely from behind and 



CO 



M cap 



Fin. 93. Side view of larynx, utter exarticula- 

 tion and removal of left plate of thyroid 

 cartilage. (Henle.) Sat, articular surface of 

 thyroid with cricoid ; (jap and ( 'al, crico- 

 arytenoid muscles, posterior and lateral ; 

 co, cartilage of Santorini, below which the 

 arytenoid and thyro-epiglottidean muscles 

 (Fig. 91) are seen in profile. 



ct 



Fie. 94. Frontal section of larynx, the anterior 

 half viewed from behind. (Henle.) t, thyroid; 

 cr, cricoid ; a, plica ary-epiglottica ; Taep, 

 thyro-ary-epiglottidean muscle ; Toe and 

 Tai, thyro-aryitenoid muscles, external and 

 internal : 1, tubercle of epiglottis ; 2, 3, ven- 

 tricle ; 4, plica thyreo-arytaenoidea superior 

 or false vocal cord; 5, plica thyreo-ary- 

 taenoidea inferior, or true vocal cord. 



above, forward and downward, viz. in the opposite direction to the 

 posterior crico-arytenoid or abductor of the glottis. 



The tension of the vocal cords is especially due to the crico- 

 thyroid muscles, which in contracting raise the front part of the 

 cricoid towards the thyroid, and depress the posterior part of 

 the cricoid and consequently of the two arytenoids which rest 

 upon it (Longet). The effect of this rotation of the cricoid on 

 its transverse horizontal axis is to increase the distance between 

 the points of insertion of the vocal cords and thus to stretch 

 them. In order that the vocal cords may be stretched, it is necessary 

 that the two arytenoid cartilages should be firmly fixed, so that 



