264 A MANUAL OF PHYSIOLOGY 



mental tone. The others are called partial or over-tones, 

 or harmonics of the fundamental tone, their vibration 

 frequency being twice, three times, four times, etc., that of 

 the latter. Now, the fundamental tone of a compound note 

 or clang produced by two musical instruments may be the 

 same, while the number, period, and intensity of the har- 

 monics are different ; and this difference the ear recognises 

 as a difference of timbre or quality. The timbre of the voice 

 depends for the most part on partial tones produced or in- 

 tensified in the upper resonance chambers. 



FIG. 93. DIAGRAM OF LARYNGOSCOPE. 



A great deal of our knowledge as to the mode and 

 mechanism of the production of voice has been acquired 

 by means of the laryngoscope (Fig. 93). 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 



