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 a 

 ring with the broad part on the 

 posterior side (cr, Fig. 14). 



2. The thyroid (tk) consists of 

 two perpendicular plates which 



meet at a right angle in front; the FlG I4 

 posterior border is continued up- 

 ward as the large horn, and down- 

 ward as the small horn (a). The ar, arytenoid ; ' m, processus 



points of the small horns form joints 

 with the sides of the cricoid. The coid ; 



/-,,..., i., ment of the thyroid cartilage 



axis Of this joint around which the during con raction of the crico- 



thyroid turns is horizontal from th 7 roid ( M - cric > thyr.}. 

 right to left. 



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



m 



M.cric.thyr. 



PROFILE OF THE 

 LARYNX. 



th, thyroid cartilage; a, smaller 

 horn of the thyroid cartilage; 



direction of move- 



