VOICE AND SPEECH. 259 



The arytenoid muscle assists in the closure of the aperture of the 

 glottis. 



The inferior laryngeal nerve animates all the muscles of the larynx, 

 with the exception of the crico-thyroid. 



Movements of the Vocal Cords. During respiration the move- 

 ment of the vocal cords differ from those occurring during the pro- 

 duction of voice. 



At each inspiration the true vocal cords are widely separated, and 

 the aperture of the glottis is enlarged by the action of the crico- 

 arytenoid muscles, which rotate outward the anterior angle of 

 the base of the arytenoid cartilages ; at each expiration the larynx 

 becomes passive ; the elasticity of the vocal cords returns them to 

 their original position, and the air is forced out by the elasticity of 

 the lungs and the walls of the thorax. 



Phonation. As soon as phonation is about to be accomplished, 

 a marked change in the glottis is noticed with the aid of the 

 laryngoscope. The true vocal cords suddenly become approximated 

 and are made parallel, giving to the glottis the appearance of a nar- 

 row slit, the edges of which are capable of vibrating accurately and 

 rapidly ; at the same time their tension is much increased. 



With the vocal cords thus prepared, the expiratory muscles force 

 the column of air into the lungs and trachea through the glottis, 

 throwing the edges of the cords into vibration. 



The pitch of sounds depends upon the extent to which the vocal 

 cords are made tense and the length of the aperture through which the 

 air passes. In the production of sounds of a high pitch, the tension 

 of the vocal cords becomes very marked and the glottis diminished 

 in length. When sounds having a low pitch are emitted from the 

 larynx, the vocal cords are less tense and their vibrations are large 

 and loose. 



The quality of voice depends upon the length, size, and thickness 

 of the cords, and upon the size, form, and construction of the 

 trachea, the larynx, and the resonant cavities of the pharynx, nose, 

 and mouth. 



The compass of the voice comprehends from two. to three octaves. 

 The range is different in the two sexes, the lowest note of the 

 male being about one octave lower than the lowest note of the 

 female ; while the highest note of the male is an octave less than the 

 highest note of the female. 



