520 ACTIONS OF THE LARNYX : VOICE. 



larynx sets them in vibration, in a manner very much resem- 

 bling that in which the reed of a Hautboy or Clarionet, or the 

 tongue of an Accordion or Harmoninm, is set in vibration by 

 the current of air that is made to pass beneath them. The 

 rapidity of the vibrations, and consequently the pitch of the 

 sound ( 523), depends on the degree of tension or tightness 

 of the vocal ligaments ; and this is regulated by muscles which 

 act upon the thyroid and arytenoid cartilages. If the thyroid 

 cartilage be drawn forwards, and the arytenoid cartilages back- 

 wards, the two ends of the vocal cords will be further sepa- 

 rated from each other, and they will consequently be tightened ; 

 by the contrary movements they will be relaxed. 



683. It is on account of the greater length of the vocal 

 cords, that the pitch of the voice is much lower in Man than 

 in Woman ; but this difference does not arise until the end 

 of the period of childhood, the size of the larynx being about 

 the same in the Boy and Girl up to the age of 14 or 15 years, 

 but then undergoing a rapid increase in the former, whilst it 

 remains nearly stationary in the latter. Hence it is that Boys, 

 as well as Girls and Women, sing treble ; whilst Men sing 

 tenor which is about an octave lower than the treble, or bass 

 which is lower still. 



684. The cause of the variations of timbre or quality in 

 different voices, is not certainly known ; but it appears to be 

 due, in part, to differences in the degree of flexibility and 

 smoothness in the cartilages of the larynx. In women and 

 children these cartilages are usually soft and flexible, and 

 their voices clear and smooth ; whilst in men, and in women 

 whose voices have a masculine roughness, the cartilages are 

 harder, and are sometimes almost completely ossified. The loud- 

 ness of the voice depends in part upon the force with which the 

 air is expelled from the lungs ; but the variations in strength 

 of voice which exist among different individuals, are in some 

 measure due to the degree in which its resonance is increased 

 by the vibration of the other parts of the larynx and of the 

 neighbouring cavities. In the Howling Monkeys of America, 

 there are several pouches which open from the larynx, and are 

 destined to increase the volume of tone that issues from it ; 

 one of these i excavated in the substance of the hyoid bone 

 itself, which is very greatly enlarged ; and to this bony drum 

 seems due the mournful plaintiveness which characterises the 



