244 STUDIES IN ADVANCED PHYSIOLOGY. 



rowed. When, now, the air is driven past these stretched 

 membranous flaps they are set in vibration and the tone 

 arises. 



3. Movements which bring aboitt the change of the 

 pitch. Any one familiar with musical instruments is aware 

 that there are two ways in which to heighten the pitch of a 

 string, or in this case a membrane. One method is to in- 

 crease its tension, as we do by tightening a violin string, 

 the other by shortening the string, a procedure also used on 

 the violin, where, by the placing of the finger, the length of 

 the string is varied to suit the pitch. Both of these methods 

 are used in the larynx. 



First, the vocal cords are stretched. This is accom- 

 plished by the contraction of muscles which lie towards the 

 front of the larynx, extending from the cricoid band to the 

 thyroid cartilage above it. This is the crico-thyroid mus- 

 cle, one of which lies on each side of the larynx. When 

 these muscles contract they pull the thyroid cartilage down 

 toward the cricoid. The cricoid band being fastened se- 

 curely to the upper portion of the trachea, is immovable, and 

 so the only motion possible is the downward one of the thy- 

 roid above it. But as the vocal cords are attached in front 

 to the thyroid cartilage they will be pulled down with it and 



Fig. 95. TO SHOW THE MANNER OF PRODUCING CHANGES IN THE PITCH OF HUMAN 



VOICE. (Martin). 



For the explanation of figures see text. 



will therefore be stretched. Reference to Figure 95 will 

 make this clear. Here c is the signet of the cricoid carti- 



