136 



PHYSIOLOGY 



CHAP. 



which are thrown into vibration by the expiratory blast, remain 

 regular. 



The two true vocal cords which extend from their anterior 

 insertion on the thyroid to the vocal processes of the arytenoids, 

 into which they are inserted posteriorly, form the pars vocalis of 

 the glottis, the average length of which in the adult male is 18 '2 

 mm. according to Miiller, 17'5 mm. according to Harless, in the 

 female 12*6 mm. according to Miiller, 13'5 mm. according to Harless. 

 The posterior part of the glottis, which is 7'8 mm. long, and 



FIG. 91. Larynx from behind, after removing a portion of the aryepiglottidean fold and upper 

 posterior portion of left thyroid cartilage. (Henle.) Taep, thyro-ary-epiglottidean muscle ; 

 Cap, posterior crico - arytenoid muscle; A, arytenoid muscle; x, kerato cricoid muscle; 

 kcps, posterior, superior, kerato-crieoid ligament ; oo, cartilage of Santorini ; *, mucous glands 

 in the aryepiglottic fold. 



extends from the posterior ends of the vocal cords to the intra- 

 arytenoid fold, is bounded by the arytenoids, and is known as the 

 rima glottidis respiratoria or intercartilaginea. 



The laryngeal muscles dilate and constrict the glottis, and 

 extend and relax the vocal cords. These effects for the most, part 

 depend not on the action of a single muscle, but on the co-ordinated 

 play of several, which makes it harder to obtain any exact know- 

 ledge of the function of each separate muscle when they are 

 working together. 



The two posterior crico-arytenoid muscles are the chief, if not 

 the only dilators of the glottis; owing to their attachments 

 and the oblique course of their fibres they rotate the bases of the 



