500 VOICE AND SPEECH. 



undergoes a marked change. A nearly passive organ, open- 

 ing widely for the passage of air into the lungs, because the 

 inspiratory act has a tendency to draw its edges together, 

 and entirely passive in expiration, it has now become a sort 

 of musical instrument, presenting a slit with borders capable 

 of accurate vibration. 



The approximation of the posterior extremities of the 

 vocal chords and their tension by the action of certain of 

 the intrinsic muscles are accomplished just before the vocal 

 effort is actually made. The glottis being thus prepared for 

 the emission of a particular sound, the expiratory muscles 

 force air through the larynx with the required power. It 

 seems wonderful how a carefully-trained voice can be modu- 

 lated and varied in all its qualities, including the intensity of 

 vibration, which is so completely under control ; but when we 

 consider the changes in its quality, we must remember, in 

 explanation, the varying conditions of tension and length 

 of the vocal chords, the differences in the size of the larynx, 

 trachea, and vocal passages generally, and the different 

 relations that the accessory vocal organs can be made to 

 assume. The power of the voice is simply due to the force 

 of the expiratory act, which is regulated chiefly by the antag- 

 onistic relations of the diaphragm and the abdominal muscles. 

 From the fact that the diaphragm, as an active inspiratory 

 muscle, is exactly opposed to the muscles which have a ten- 

 dency to push the abdominal organs, with the diaphragm 

 over them, into the thoracic cavity, and thus diminish the 

 pulmonary capacity, the expiratory and inspiratory acts can 

 be balanced so nicely that the most delicate vocal vibrations 

 can be produced. It is unnecessary to refer more in detail 

 to the action of these muscles, as we have already treated of 

 this subject fully in another volume. 1 



The glottis, thus closed as a preparation to a vocal act, 

 presents a certain amount of resistance to the egress of air. 

 This is overcome by the action of the expiratory muscles, 



1 See vol. i., Respiration, p. 385, et seq. 



