VOICE 



305 



A great deal of our knowledge as to the mode and mechanism of 

 the production of voice has been acquired by means of the laryngo- 

 scope (Fig. 143). This consists of a small plane mirror mounted on 

 a handle, which is held at the back of the mouth in such a position 

 that a beam of light, reflected from a larger concave mirror fastened 

 on the forehead of the observer, is thrown into the larynx of the 

 patient. The observer looks through a hole in the centre of the' 

 large mirror; and an image of the interior of the larynx is seen in 

 the small mirror, in which the parts that are anterior appear as 

 posterior, the arytenoid cartilages in front, the thyroid behind, and 

 the vocal cords stretching between. The small mirror is warmed to 

 body-temperature before being introduced, so as to prevent the 

 condensation of moisture on it. The tendency to retch, which is 



Lamp 



Concave Mirror 



Larynx. 



Fig. 143. Diagram of Laryngoscope. 



caused by contact of the instrument with the soft palate, may be 

 removed or lessened by the application of a solution of cocaine. 



Examined with the laryngoscope during quiet respiration, the 

 glottis is seen to be moderately, though not widely, open, and the 

 vocal cords almost motionless. Although the portion between the 

 arytenoid cartilages has received the name of glottis respiratoria, in 

 contradistinction to the glottis vocalis between the vocal cords, the 

 rima in its whole extent from front to back is really concerned in 

 the respiratory act. In deep expiration the vocal cords come nearer 

 to the middle line, and the glottis is narrowed ; in deep inspiration 

 they are widely separated, and the rings of the trachea, and even 

 its bifurcation, may be disclosed to view. When a sound is produced 

 a note sung, for example the cords are approximated (Figs. 144 

 and 145) ; and with a high note more than with a low. 



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