VOICE. 



1477 



If the larynx of an animal be dissected out, 

 and the vocal cords be stretched, they will 

 vibrate like a piece of caoutchouc or leather 

 in a current of air. In conducting these ex- 

 periments, it is necessary to secure the same 

 conditions as those which are required in the 

 laminae above mentioned ; for instance, the 

 inner edges of the glottis must be turned 

 towards each other till they are in the same 

 plane and parallel to one another before they 

 will produce any sound ; hence we infer, that 

 when the tension of the arytenoid ligaments 

 takes place in the living animal, they turn upon 

 their axes till their planes (which in the state 

 of relaxation are inclined to the axis of the 

 vocal tube) become perpendicular to it, and as 

 the edges of the glottis approximate, and its 

 chink is nearly or entirely closed up, they 

 acquire the true vibrating position. The 

 production of the most simple tones of voice 

 requires the associated actions of a most 

 extensive range of organs ; and it is calculated 

 that in the ordinary modulation of the voice, 

 more than one hundred muscles are brought 

 into action at the same time. 



The lungs having been first supplied with 

 air by the act of inspiration, and the air in 

 the chest and trachea having subsequently 

 been condensed by the muscles of expiration, 

 a portion of the edges of the glottis yields to 

 its pressure, and is curved upwards, so as to 

 form an angle with the axis ( f the vocal 

 tube, leaving between them a narrow aperture 

 through which the air escapes. The tension 

 and elasticity of the vocal ligaments tend to 

 restore them to the plane of the vibrating 

 position ; the air having been rarefied below 

 the glottis during their elevation, becomes 

 condensed on their depression, and the ne- 

 cessary force is again accumulated to re- 

 elevate the vocal ligaments, and thus an oscilla- 

 ting movement, consisting of a partial opening 

 and closing of the glottis, takes place, which 

 being communicated to the contiguous air, 

 the sounds of the voice are produced. 



The relative length of the vibrating edge of 

 the glottis is regulated by the pressure of the 

 column of air in the trachea, and the resistance 

 of the vocal ligaments. The intensity of the 

 voice in the same medium, and under similar 

 collateral circumstances, depends on the 

 pressure of the column of air in the trachea, 

 and the range of motion performed by the 

 vibrating edges of the glottis. The vocal 

 ligaments do not vary the pitch of the voice 

 by their tension alone, but by their variations 

 in length and tension conjointly. The author 

 has learnt this from his own experiments on 

 the vocal functions of the larynx, which have 

 becrn confirmed both by Majendie and Mayo ; 

 the former having observed in the larynx of a 

 dog that a longer portion of the ligaments of 

 the glottis vibrated during the utterance of 

 grave tones, and that the length was dimi- 

 nished as the tones became acute. The latter 

 had an opportunity of inspecting the move- 

 ments of the glottis in a man who had made 

 an attempt to destroy himself by cutting his 



Fig. 89]. 



The Head and Vocal Organs prepared for experi- 

 ments. (After Mttller.) 



The cervical vertebrae are removed, and the oeso- 

 phagus opened behind the arytenoid cartilages, 

 which are fixed together by a strong pin and 

 ligature ; the latter is brought through the open- 

 ing, which is then firmly sewed together, and the 

 lower opening of the oesophagus is also closed up. 

 The larynx is laid bare, and the superior portion of 

 the thyroid cartilage carefully removed so as not 

 to injure the mucous membrane of the larynx. 

 The parts thus prepared are firmly fixed against 

 the column, to which the arytenoid cartilages are 

 also attached by the cord which binds them to- 

 gether. The trachea is connected with a pipe 

 and bellows for the supply of air. 



a, the trachea; b, the os'hyoides; c, the cricoid 

 cartilage ; d, portion of the thyroid cartilage re- 

 maining for the attachment of the cords e, by 

 means of which the vocal cords may be extended ; 

 /, apparatus for compression. 



Fig. 892. 



The apparatus used for the lateral compression of the 

 vocal cords, as seen in fig. 891 f. 

 5 B 3 



