156 



ZOOLOGY. 



themselves. In the interior of the organ, this mucous 

 membrane forms four folds, two superior!} 7 ', called the false 

 vocal cords, and two inferiorly, called the true vocal cords. 



Fig. 110. White-throated Sapajou, or Sajou, Cebus hypoleucos. 



It is here, upon the edge of these folds, by the air impinging 

 and causing them to vibrate, that the voice is formed. 

 (Figs. 112 and 113.) 



These folds are in consequence called the vocal cords or 

 ligaments of the glottis, the space between the true ligaments 

 being called the glottis or rima glottidis } the true vocal cords 

 are formed interiorly of folds of mucous membrane, and ex- 

 teriorly of elastic ligaments, which stretch from the interior 

 of the salient angle of the thyroid cartilage to the arytsenoid 

 cartilages. By the muscular apparatus attached to the larynx, 

 not only the entire larynx can be moved up and down in the 

 neck, but these ligaments or true vocal cords can be made 

 tense or relaxed, so as to diminish, enlarge, or all but close 

 the aperture called rima glottidis, through which the air must 

 pass and repass in its way to and from the lungs. Between 



