CHAPTER XVI. 



THE VOICE AND SPEECH. 



The Larynx. In nearly all air-breathing vertebrate animals there 

 are arrangements for the production of sound, or voice, in some parts of 

 the respiratory apparatus. In many animals, the sound admits of being 

 variously modified and altered during and after its production; and, in 



Cornumin: 



Cornu sup; - 



,i, Sterno-hyoideua, 



m. Stcmo-hyoideua, 



. Sterno-hyoidexia, 



. Crico-tliyroideus* 



g : crico-thyr. med; 



Cart: cricoidea-. 

 lag: crico-tracheae. 



Cart: tracheale. <- 



Fio. 302. The Larynx, as seen from the front, showing the cartilages and ligaments. The 

 muscles, with the exceptions of one crico-thyroid, are cut off short. (Stoerk.) 



man, one such modification occurring in obedience to dictates of the 

 cerebrum, is speech. 



It has been proved by observations on living subjects, by means of 

 the laryngoscope (p. 441), as well as by experiments on the larynx taken 

 from the dead body, that the sound of the human voice is the result of 

 the vibration of the inferior laryngeal ligaments, or true vocal cords (A, 

 cv, Fig. 307) which bound the glottis, caused by currents of expired air 

 impelled over their edges. If a free opening exists in the trachea, the 

 sound of the voice ceases, but it returns if the opening is closed. An 

 opening into the air-passages above the glottis, on the contrary, does not 

 prevent the voice being produced. By forcing a current of air through 

 the larynx in the dead subject, clear vocal sounds are elicited, though 



