1454 THE VOICE. [BOOK m. 



If the voice, and especially if a high note, be uttered the view 

 changes (Fig. 186 A); besides an alteration in the form of the 

 laryngeal aperture, the vocal cords are seen to be brought close 

 together and nearly parallel so that the glottis becomes a mere slit. 

 If no voice is being uttered and a deep inspiration be taken 

 changes of another kind may be observed (Fig. 186 C) ; the glottis 

 becomes a wide aperture with the form of a truncated rhomboid, 

 the obtuse angle on each side marking the attachment of the 

 vocal cord to the processus vocalis ; through this wide opening the 

 tracheal rings are clearly visible, and indeed with an appropriate 



C'tion of the mirror the bifurcation of the trachea into the 

 ichi may under favourable circumstances be observed. When 

 changes in the voice or in the breathing are being made, the white 

 glistening vocal cords may be seen to come together or to go apart 

 like the blades of a pair of scissors. 



905. Laryngoscopic observation then teaches that the larynx 

 is used not only for the utterance of voice, for phonation, but also for 

 breathing ; and indeed in speaking of respiration ( 336) we called 

 attention to this ; but the former is its more important use and we 

 may chiefly dwell on this, referring incidentally to the respiratory 

 functions. 



In order that the membranous edges of an aperture may be 

 readily thrown into sonorous vibrations by a blast of air, the edges 

 should be brought near together and the aperture reduced to a 

 mere slit. Hence the fundamental condition for the formation of 

 the voice, and indeed speaking generally of voices of all kinds, 

 is the approximation and consequent more or less parallelism of 

 the vocal cords. 



In the voice, as in other sounds (cf. 841), we distinguish three 

 fundamental features : (1) Loudness. This depends on the strength 

 of the expiratory blast. (2) Pitch. This depends on the rapidity 

 of the vibrations, and this we may in a broad way consider as 

 determined on the one hand by the length and on the other 

 hand by the tension of the vocal cords. What we may call the 

 natural length of the vocal cords is constant, or varies only 

 with age ; and the influence of this factor bears on the general 

 range of the voice, not on the particular note given out at any one 

 time. The tension of the vocal cords on the contrary is very 

 variable, and the pitch of any particular note uttered depends 

 in the main on this; hence great importance attaches to the 

 mechanisms by which changes in the tension of the vocal cords 

 are brought about. But, as we shall see, the problems connected 

 with the compass of a voice and with changes of pitch are very 

 complex ; in considering these things we have to do with much 

 more than mere variations in the tension of the vocal cords along 

 the whole of what we have called their natural length. These 

 matters however we shall deal with later on, and may for the 

 present consider tension as the main factor of changes in pitch. 



