CHAPTER XXIX 



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 fore- 

 head. The subject is asked to open his mouth, incline his head slightly back- 

 wards, protrude his tongue, and to 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 backwards until it touches the uvul&. 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 be asked to sound a high note the vocal cords may be seen 

 to come together and to vibrate, and if he be asked to take a deep breath they 

 separate, and the interior of the trachea and even its bifurcation may 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 application of a solution of 

 cocaine to the mucous membrane. 



The movements of the laryngeal cartilages are studied in a model which re- 

 presents 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 shape and size of 

 the resonating chamber formed by the throat and buccal cavity. 



The production of consonants. Notice that most of the consonants are 

 produced by an interruption, completed and incompleted, of the blast of air 

 which is producing the vibration of the vocal cords, the interruption occurring 

 either at the back of the palate (gutturals) or at the front of the palate (linguals), 

 or at the lips (labials). Notice also that the character of the interruption is a 

 factor in determining the quality of the consonant : thus, with some, such as 

 k, b, and t, it is sudden or explosive : with others, such as m and n, the nasal 

 cavities are brought in as resonators : with others, such as ch, f, and s, the 

 blast is continuous, but is made to traverse a narrowed part of the cavity : 

 whilst with q there is an actual vibration of the narrowed part. 



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