PRONATION 551 



quiet respiration, the glottis is moderately large, becoming smaller 

 on expiration. Moreover, by forced inspiratory efforts, the size of 

 this communication may be increased in such a measure that the upper 

 rings of the trachea, and even the bifurcation of the bronchi, are brought 

 intg view. Movements of the vocal cords also result in consequence 

 of various accessory respiratory efforts, such as are made necessary 

 during the acts of coughing, sneezing, and hiccoughing. 



The production of sounds requires not only a varying approximation 

 of the vocal cords, but also a very precise adjustment of their tenseness. 

 The former effect which, as has been pointed out above, is based 

 upon the rotation of the arytenoid cartilages around their vertical 

 axes, seems to constitute a more accurate mechanism than the latter 

 which is largely dependent upon the backward movement of these 

 cartilages in consequence of the contraction of the cricothyroid 

 muscles. 



The different laryngeal parts having been properly set, the air 

 stored in the lungs is forced outward through the narrow glottis, 

 thereby imparting a vibratory motion to 

 the vocal bands. In order to overcome 

 the resistance interposed at this level, it 

 has been found that the air-pressure in the 

 trachea necessary to cause a sound of ordi- 

 nary pitch and loudness, must be raised 

 to between 140 and 240 mm. of water. 

 Loud sounds require a pressure of as much 

 as 950 mm. of water. It should also be 

 remembered that the vibrations are not ,, ^^«- 2 7 3 .-Position of 



,.,,.,, , 11, 1 Vocal Cords on Uttering a 



restricted to the vocal cords, but are also high Note. (Landois.) 

 transferred to the air contained in the outer 



respiratory passage as well as to that filling the trachea and bronchi. 

 Thus, we speak of a chest voice and a falsetto voice. Chest sounds 

 always impart a fremitus to the wall of the thorax which may be 

 perceived by placing the hands over the lower air-passage, from which 

 the resonance is obtained. Falsetto sounds derive their resonance 

 principally from the pharyngeal, oral and nasal cavities. In general, 

 therefore, it may be said that the vocal mechanism embraces: (1) 

 the motive expiratory blast of air, (2) the larynx which gives rise 

 to the fundamental sound, (3) the thorax, pharynx, mouth and nose 

 which modify the primary sound and give color to it, and (4) the 

 organs employed in articulating the sounds. 



The Characteristics of Sounds. — The action of the vocal cords 

 may be imitated in a crude way by placing a short tube of a diameter 

 of about 2 cm. against the palmar surfaces of two adjoining fingers. 

 By blowing into the free end of this tube a sound will be produced 

 in consequence of the vibrations of the folds of skin along the two fingers. 

 A similar purpose is served by the so-called artificial larynx which 

 consists of a piece of tubing, one end of which is partially closed by 



