CHAPTER XXXI 



The Production of Vocal Sounds. Analysis of Sounds. 

 Audition. Semicircular Canals 



Use of the laryngoscope. The laryngoscope consists of a small circular 

 plane mirror fixed to a handle at a suitable angle; a large concave 

 mirror with a hole in the centre is strapped to the operator's forehead. 



Method of procedure. Practise first on an artificial model of the 

 larynx and afterwards on the living subject. The latter is placed on a 

 stool with a lamp over his right shoulder, a little above the level of 

 his mouth. The observer sits opposite and close to the subject with 

 the large mirror attached to his forehead. The subject is asked to 

 open his mouth, incline his head slightly backwards, protrude his 

 tongue, and hold it down with a handkerchief. The observer 

 manoeuvres his head until the back of the subject's throat is brightly 

 illuminated ; he then takes the small mirror in his right hand, warms 

 it slightly in a flame to prevent moisture condensing on its surface 

 (the back of the mirror should be just perceptibly warm to the cheek), 

 and, holding the handle as one does a pen, pushes it horizontally back- 

 wards until it touches the uvula. First the dorsum of the tongue is 

 seen in the mirror, then, as the handle is depressed, the epiglottis ; 

 then the glottis and vocal cords come into view. The image of the 

 larynx thus obtained is an inverted one. In ordinary breathing the 

 glottis is open if the patient is asked to sound a high note the vocal 

 cords may be seen to come together and to vibrate, and if he is asked 

 to take a deep breath they separate ; the interior of the trachea and 

 even its bifurcation may then be seen through the widely open glottis. 



Should there be a tendency to retch when the mirror comes in 

 contact with the soft palate, this may be diminished by the applica- 

 tion of a solution of cocaine to the mucous membrane. 



The movements of the laryngeal cartilages are studied in a model 

 which represents them articulated together. The action of the muscles 

 can be imitated by threads, and the vocal cords by thin flat rubber 

 bands stretched between the thyroid and arytenoids. 



The production of vowel sounds. Notice that the production of 

 the vowel sounds (ah, eh, ee, o, oo) is accompanied by changes in the 



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