210 f HUMAN PHYSIOLOGY 



whose bases are movably articulated with the posterior parts 

 of the upper surface of the cricoid. 



The vocal cords are foldlike processes of the inner wall 

 of the larynx, which in front are attached to the posterior 

 wall of the thyroid ; at the rear they are attached to the vocal 

 processes, which are anterior processes of the triangular 

 bases of the arytenoids. During quiet breathing the space 

 between the vocal cords and the two arytenoids, called the 

 glottis, is open. The glottis has the form of an isosceles 

 triangle (Fig. 16, I). When the glottis, for production of 

 voice, must be narrowed, the arytenoids approach each 

 other until they come into contact and the vocal cords are 

 tense. 



A. In the closing of the glottis, the following parts func- 

 tion: 



1 . The transverse and oblique arytenoid muscles, which are 

 inserted on the posterior side of the two arytenoids and by 

 their contraction draw the posterior parts of the arytenoids 

 toward the median line (Figs. 15 and 16, II and III). 



2. The lateral crico- arytenoid on both sides, which pro- 

 ceeds from the lateral surface of the cricoid upward and 



]==j^._ M.aryt.tr.et obi. backward to the muscular pro- 

 cesses (lateral angle of the base 

 of the arytenoids). By the con- 

 traction of the muscles the 

 t arytenoids are turned about a 



-M.cnc.ary.post J 



vertical axis and the vocal pro- 

 cesses are drawn toward the 

 FIG. is. POSTERIOR VIEW OF ,. ,. T , ... 



LARYNX. median line. Its antagonist is 



M. aryt. tr. et obi., transverse and the posterior crico- arytenoid, 

 ^ J^rSj-^ which alone turns the vocal 

 muscle. processes outward and, in con- 



junction with the lateral, turns the whole arytenoid outward. 

 In this manner the glottis is opened. 



B. To render the vocal cords tense, the following parts 

 function : 



I. The crico-thyroid muscle, which pulls the thyroid 



