CHAPTER V 

 VOICE AND SPEECH 



Voice. Sounds of various kinds are frequently produced by the 

 movements of animals as a whole, or of individual organs. The 

 muscular sound, the sounds of the heart and of respiration, we have 

 already had to speak of. Such sounds may be considered as purely 

 accidental as the footfall of a man or the buzzing of a fly. The 

 wings of an insect beat the air, not to cause sound, but to produce 

 motion; the respiratory murmur is a mere indication that air is 

 finding its way into the lungs, it is in no way related to the oxidation 

 of the blood in the pulmonary capillaries. But in many of the 

 higher animals mechanisms exist which are specially devoted to the 

 utterance of sounds as their prime and proper end. In man the 

 voice-producing mechanism consists of a triple series of tubes and 

 chambers : (i) The trachea, through which a blast of air is blown ; 

 (2) the larynx, with the vocal cords, by the vibrations of which 

 sound-waves are set up ; and (3) the upper resonance chambers, the 

 pharynx, mouth, and nasal cavities, in which the sounds produced 

 in the larynx are modified and intensified, and in which independent 

 notes and noises arise. 



The larynx is a cartilaginous box, across which are stretched, 

 from front to back, two thin and sharp-edged membranes, the (true) 

 vocal cords. In front the cords are attached to the thyroid carti- 

 lage, one a little to each side of the middle line; behind they are 

 connected to the vocal or anterior processes of the pyramidal 

 arytenoid cartilages. The thyroid and the two arytenoids are 

 mounted upon a cartilaginous ring, the cricoid. The arytenoids 



! can rotate on the cricoid about a vertical axis, while the cricoid can 

 rotate on the thyroid cartilage around a transverse horizontal axis. 

 The cricoid can thus be raised by the contraction of the crico- 

 thyroid muscle, and the vocal cords stretched. By the pull of the 

 posterior crico-arytenoid muscles, attached to the external or mus- 



i cular processes of the arytenoid cartilages, the vocal processes are 

 rotated outwards, the cords separated from each other or abducted, 

 and the chink between them, the rima glottidis, widened. When 



:i the vocal processes are approximated by contraction of the lateral 



307 



