CHAPTER XXVII. 



VOICE AND SPEECH. 



The human voice is produced by an expiratory blast of air 

 being forced through the narrow opening at the top of the wind- 

 pipe called the glottis. This glottis, which lies in the lower 

 part of the larynx, is bounded on each side by the edges of thin, 

 elastic, membranous folds that project into the air passages. 

 These membranous folds, called the vocal cords, are set vibrating 

 by the current of air from below, and in turn communicate their 

 vibrations as sound to the air in the air passages situated above 

 them. 



ANATOMICAL SKETCH. 



The vocal apparatus is really a musical instrument of the reed- 

 pipe kind. If we compare i$ with the pipe of an organ, we find 

 all the parts of the latter represented. The lungs within the 

 moving thorax act as the bellows. The bronchi and trachea are 

 the supply pipes and air box. The vocal cords are the vibrating 

 tongues ; while the larynx, pharynx, mouth, and nose act as the 

 accessory or resonating pipes. The blast of air is produced and 

 regulated by the respiratory muscles ; and special intrinsic mus- 

 cles of the larynx change the condition of the vocal cords so as 

 to alter the pitch of the notes produced. Other sets of muscles, 

 by altering the condition of the resonating pipes, give rise- to 

 many modifications in the vocal tones, and thus produce what 

 is called speech. 



The larynx, which may be regarded as the special organ of 

 voice, is, in the main, made up of four cartilages, viz., the cricoid, 

 thyroid, and two arytenoids, jointed together so as to allow of con- 

 siderable motion. Of these the inferior, the cricoid, is attached 

 to the trachea, which it joins to the others. It forms a ring, which 

 is thin in front, but deep and thick behind, owing to a peculiar 

 projection upward of its posterior part. The thyroid consists of 

 two side wings so bent as to form the greater part of the anterior 



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