150 HUMAN PHYSIOLOGY. 



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 diminishes in length. When grave 

 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 the size, form and construction of the trachea, 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 voices, e. g., bass, baritone, tenor, contralto, mezzo- 

 soprano and soprano, are due to the length of the vocal cords ; 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 combination 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 consonantal sounds are produced in the air passages above the larynx 

 by an interruption of the current of air by the lips, tongue and teeth ; the 

 consonants may be divided into: (i) mutes, , d, /,/, /, c> g ; (2) dentals, 

 d,j, s, t, z ; (3) nasals, m, n, ng ; (4) labials, ^, /,_/",#, m ; (5) gutturals, 

 /, g, c> and g hard ; (6) liquids, /, m, n, r. 



