210 SPECIAL PHYSIOLOGY. 



drawing with it, at the same time, the trachea; but the mode in which 

 the trachea and the attached vocal tube, or parts above the glottis, 

 influence the voice, is not yet determined. The experiments of Muller 

 on the human larynx, show that alterations in the length of the wind- 

 tube and of the attached tube, have but little or no effect on the pitch 

 of the voice; whereas, as already stated, alterations in the length of 

 these tubes modify very considerably the pitch of the notes of arti- 

 ficial, rigid, and membranous tongues. According to this physiologist, 

 the alteration in the 'length of the attached vocal tube, produced by 

 the ascent and descent of the larynx, is not more than an inch, and 

 does not modify the height of the notes, the increase or diminution in 

 the length of the tube, produced by the depression or elevation of the 

 larynx, merely affording increased facility for the formation of the 

 low or high notes. It is, however, maintained by some, that the total 

 length of the trachea, with the cavities above the glottis, is in reality 

 shortened by the ascent of the larynx, the trachea rising out of the 

 thorax, almost as much as the larynx ascends; but, considering that 

 the actual alteration in length is so slight as not to account for the 

 changes in the pitch of voice, they are of opinion that a diminution in 

 the diameter of the trachea, produced by the upward movement of the 

 larynx, together with variations in the tension of its walls, enables it 

 to accommodate itself to the different vocal tones. (Wheatstone and 

 Bishop.) The trachea may, in being drawn upwards, be narrowed by 

 about one-third of its diameter. 



In the production of the higher notes of the voice, the thyro-aryte- 

 noid muscles take an active part. As already stated, the pitch of the 

 note of a membranous tongue is heightened when the calibre of that 

 part of the wind-tube nearest to the tongue is lessened. The thyro- 

 arytenoid muscles, by narrowing the diameter of the larynx, just 

 below the vocal cords, influence the voice in a similar manner. It 

 was found by Muller, that on removing these muscles from the human 

 larynx, and imitating their action, by pressing inwards the thyroid 

 cartilage on each side, below the vocal cords, higher notes were pro- 

 duced. During the ascent of the voice, the soft palate is depressed, 

 and tjie tonsils are approximated. The epiglottis, when depressed, is 

 supposed to influence the pitch of the voice, causing the notes to be- 

 come graver and duller, for partial covering of the end of the attached 

 tube of a wind instrument, as already mentioned, causes a lowering of 

 the pitch. 



The peculiar tone of the voice in different persons, or the personal 

 quality of the voice, is due to the form of the air-passages generally, to 

 the condition of the mucous membrane, and to the power of resonance 

 of those cavities: the peculiar quality of the voice, known as the nasal 

 tone, is due to similar causes. If the nostrils be closed, the natural 

 tone of the voice is not affected, so long as the arches of the palate 

 do not approach each other; when, however, they are approximated, 

 the nasal tone is produced; the larynx, at the same time, ascends 

 much higher than in the production of the natural tones. The nasal 

 tone can also be produced, when the external apertures of the nares 

 are open, whether the mouth be closed or not; the larynx is then 



