SPECIAL PHYSIOLOGY OF THE MUSCLES 



209 



zontal plane is about 3 kilogrammetres for each step; during 

 running it is more. This work is, however, not lasting, 

 since, during each step, the elevation of the body is lost. 



3. VOICE AND SPEECH 



1. Production of voice. The larynx with the vocal 

 cords forms a reed organ with membranous reeds. During 

 the production of voice the inner borders of the vocal cords 

 approach each other and are stretched. When, now, the 

 expired air passes through the larynx, the vocal cords 

 vibrate. By this vibration of the cords, the glottis alter- 

 nately opens and closes so that the expired air is emitted 

 intermittently. In this manner, vibrations of the air are 

 produced which are strengthened by the resonance of the 

 pharynx and mouth and can be perceived as sounds by the 

 ear. 



(a) The mechanism of 'the vocal chords. The cartilages 

 concerned in the study of the vocal 

 cords are : 



The cricoid, a cartilaginous ring 

 at the upper part of the tracheal 

 wall; it has the form of a signet 

 ring with the broad part on the 

 posterior side (cr, Fig. 14). 



2. The thyroid (t/i) consists of 

 two perpendicular plates which 

 meet at a right angle in front ; the 

 posterior border is continued up- 

 ward as the large horn, and down- 

 ward as the small horn (a). The 

 points of the small horns form joints 

 with the sides of the cricoid. The 



M.cric.thyr. 



FIG. 



14. PROFILE OF THE 



LARYNX. 



///.thyroid cartilage; a, smaller 

 horn of the thyroid cartilage; 

 a>\ arytenoid ; ///, processus 

 muscular is ; r, processus voca- 

 lis ; <//, vocal chords; cr, cri- 

 coid; />-/>, direction of move- 

 cartilage 



c ,. . . . A ment of the thyroid 



axis ol this joint around which the during contraction of the crico- 

 thyroid turns is horizontal from thyroid (J/. eric. Mrr.). 

 right to left. 



3. The arytenoids (ar) arc two three-sided pyramids 



