Page:Encyclopædia Britannica, Ninth Edition, v. 24.djvu/300

Rh 276 VOICE distinctions are of more importance practically than as implying any marked physiological differences in the mechanism of the larynx during the production of the tones in the different registers. By means of the laryn goscope it is possible to see the condition of the rima glottidis and the cords in passing through all the range of the voice. In 1807 Bozzini first showed that it was possible to see into the dark cavities of the body by illumining them with a mirror, and in 1829 Babington first saw the glottis in this way. In 1854 Garcia investigated his own larynx and that of other singers, and three years later Tiirck and especially Czermak perfected the construction of the laryngoscope. In 1883 Lennox Browne and Emil Behnke obtained photographs of the glottis in the living man. The laryn goscope is a small mirror, about the diameter of a shilling, fixed to the end of a long handle at an angle of 125 to 130. This mirror is gently pushed towards the back of the throat, and if sufficient light be thrown into the mouth from a lamp, and if the eye of the observer be in the proper position, by angling the small mirror it is not difficult to get a view of the glottis. The light from the lamp is reflected by the mirror down on the glottis, from this it is reflected back to the mirror, and then by the mirror it is finally reflected to the eye of the observer. Usually the observer has in front of his eye a mirror by which a powerful beam of light can be thrown from a lamp into the mouth and throat. In the centre of the mirror there is a small hole through which the eye of the observer sees the image in the small mirror at the back of the throat. By placing a second plane mirror in front of the face, an observer can easily study the mechanism of his own larynx. 1 Suppose the picture of the larynx to be examined in the small mirror at the back of the throat, an image will be seen as in fig. 4. During calm breathing, the glottis is lance-shaped, between the yellowish white cords. A deep inspiration causes the glottis to open widely and in favourable circumstances one may look into the trachea. When a sound is to be made, the vocal cords are brought close together, either along their whole length, as in fig. 7, or only along the ligamentous portion, the space between rap Fig. 7. 8. Fio. 7. Arrangement of glottis previous to emission of a sound. 6, epiglottis ; rs, false cord ; ri, true vocal cord ; ar, arytenoid cartilages. (From Mandl.) FJG. 8. Closure of the ligamentous portion of glottis, b, epiglottis ; rs, false cord ; ri, true vocal cord ; or, space between arytenoids ; ar, arytenoid cartilages ; c, cuneiform cartilages ; rap, ary-epiglottic fold ; ir, inter-ary tenoid fold. (From Mandl.) the arytenoids being still open, as in fig. 8. Then when the sound begins the glottis opens (fig. 4), the form of the opening influencing the kind of voice, whilst the degree of tension of the cords will determine the pitch. During inspiration the edges of the true vocal cords may occasionally be close together, as in sobbing, and it has been pointed out by various observers that during inspiration the false cords are easily separated, even when they touch, and during expiration, owing to dilatation of the ventricles, they come together and may readily close. Thus, from the plane of the cords, the true cords are most easily closed during inspiration and the false cords during expiration. Wyllie clearly showed in 1865 that the false vocal cords play the chief part in closure of the glottis during expiration (Edin. Med. Jour., 1866). Lauder Brunton and Cash have confirmed Wyllie s results, and have shown further that the function of the false cords is to close the glottis and thus fix the thorax for muscular effort ; and they adduce many facts from comparative 1 A cheap and efficient form of auto-laryngoscope was constructed by the late Dr David Foulis, and may be had from Messrs. W. B. Hilliard & Son, 65 Rcnfield Street, Glasgow. anatomy in favour of this view, these cords being strongly developed in those animals whose habits render fixation serviceable, whilst, on the other hand, they are absent or weakly developed in animals where fixation is of little or no service (Jour. Anat. and Physiol., vol. xvii.). During the production of the chest voice, the space between the arytenoid cartilages is open, and between the vocal cords there is an ellipsoidal opening which gradually closes as the pitch of the sound rises (see figs. 9, 10, 11). Fig. 9. Fig. 10. FIG. 9.- Chest voice, deep tone, b, epiglottis ; or, glottis ; rs, false vocal cord ; ri, true vocal cord ; rap, ary-epiglottidean fold ; ar, arytenoid carti lages. (From Mandl.) FIG. 10. Chest voice, medium tone, orl, ligamentous portion of glottis ; ore, portion of glottis between arytenoids ; remaining description as in fig. 7. (From Mandl.) During head voice, the opening between the arytenoids is completely closed ; the portion between the vocal cords is I Fig. 11. Fig. 12. FIG. 11. Chest voice, high tone ; description same as for (igs. 7 and 8. (From Mandl.) FIG. 12. Head voice, deep tones. I, tongue ; c, epiglottis ; pe, pharyngo-epi- glottidean folds ; ae, ary-epiglottic folds ; rs, false cords ; ri, true vocal cords ; g, pharyngo-laryngeal groove*; ar, arytenoid cartilages ; c, cuneiform carti lages ; o, glottis ; r, inter-arytenoid folds. (From Mandl.) open, but in place of being almost a narrow straight slit as in chest voice, it is wide open so as to allow an escape of more air (see fig. 12). The condition of the cords during falsetto is, according to Miiller, one in which the cords can only vibrate at their margins, and especially in the middle, in consequence of the false cords pressing downwards upon them. Oertel, on the other hand, states that in falsetto the cords vibrate throughout their length, &quot; but that they form nodal lines parallel to the free borders of the loops or bellies of vibration &quot; (Beaunis). Probably in these circumstances the membranes become much thinner. Oertel also found that during the falsetto voice the epiglottis became erect, the apices of the arytenoids were directed backwards, and the whole larynx became narrower but longer from before backwards. Behnke says that, in the production of the &quot;small register,&quot; the mechanism consists in the formation of an oval orifice in the front part of the glottis which contracts the more the higher the voice ascends, the vocal ligaments being, in the hinder part, pressed together so tightly that scarcely any trace of a slit remains&quot; (Lennox Brown and Behnke, op. cit.). Illing- worth is of opinion that falsetto (and even the ordinary voice) is produced in the &quot;same way as the mouth is used in whistling&quot; (see Edin. Med. Jour., 1876). This view may be true to some extent as regards falsetto, but it will not hold good for the ordinary voice. The crico-thyroid muscle is supplied by the superior laryngeal branch of the pneumogastric nerve, and all the other muscles by the inferior or recurrent laryngeal branch