232 HUMAN PHYSIOLOGY. 



at each expiration the larynx becomes passive; the elasticity of the vocal bands 

 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 bands suddenly become approximated and are made parallel, giving to 

 the glottis the appearance of a narrow slit, the edges of which are capable 

 of vibrating accurately and rapidly; at the same time their tension is much 

 increased. 



With the vocal bands thus prepared the expiratory muscles force the column 

 of air into the lungs and trachea through the glottis, throwing the edges of 

 the bands into vibration. 



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

 very marked and the glottis diminished in length. When sounds having a low 

 pitch are emitted from the larynx, the vocal bands are less tense and their 

 vibrations are large and loose. 



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

 bands, 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. 



The varieties of voice e. g., bass, baritone, tenor, contralto, mezzo- 

 soprano, and soprano are due to the length of the vocal bands, being longer 

 when the voice has a low pitch, and shorter when it has a high pitch. 



Speech is the faculty of expressing ideas by means of combinations of sounds 

 in obedience to the dictates of the cerebrum. 



Articulate sounds may be divided into vowels and consonants. The 

 vowel sounds, a, e, i, o, u, are produced in the larynx by the vocal cords. The 

 consonant sounds are produced in the air-passages above the larynx by an in- 

 terruption of the current of air by the lips, tongue, and teeth; the consonants 

 may be divided into: 



1. Mutes, b, d, k, p, t, c, g. 



2. Dentals, d, j, s, t, z. 



3. Nasals, m, n, ng. 



4. Labials, b, p,f, v, m. 



5. Gutterals, k, g, c, and g hard. 



6. Liquids, /, m, n, r. 



