in PHONATION AND AKTICULATION 143 



movements can therefore be excited independently of the centre 

 for the thoracic respiratory movements. Unilateral stimulation 

 of this centre invariably produces bilateral effects, i.e. abduction 

 of both vocal cords and widening of the glottis. 



The movements of phonation have also a separate centre in the 

 bulb. After separating the brain from the bulb, Vulpian was able 

 reflexly to elicit cries, as though the animal still reacted to the 

 painful effects of stimulation. Semon and Horsley on stimulating 

 the ala cinerea and upper margin of the calamus scriptorius, 

 obtained energetic closure of the glottis, or adduction of both 

 vocal cords, when the animal was not too profoundly narcotised. 



Since phonation is a voluntary act, perfected by practice, it is 

 regulated by special cortico- cerebral centres which control the 

 action of the bulbar laryngeal centres. 



The cortical centres in the Macacus monkey lie in the lowest 

 part of the pre-central or ascending frontal convolution ; and in 

 dogs, in the lowest part of the pre-crucial part of the sigmoid 

 gyrus. Electrical stimulation of this area, in either hemisphere, 

 produces adduction of both vocal cords which lasts as long as the 

 stimulation (Semon and Horsley). But if this is unduly pro- 

 tracted the need of breathing causes a pronounced dilatation 

 of the glottis, which momentarily interrupts its closure. 



In man the area of phonation and articulate language is far 

 more developed ; it lies at the foot of the third frontal convolution, 

 and acquires a much higher functional significance in the left 

 hemisphere than in the right. This important subject will be 

 discussed more fully in Chapter IX. 



Extirpation of both cortical speech centres does not paralyse 

 the glottis in animals. After unilateral extirpation stimulation 

 of the centre in the other hemisphere produces the same effect 

 closure of the glottis as was previously obtained. 



Unduly strong or protracted stimulation of the cortical centre 

 of phonation may induce an epileptic attack which begins in the 

 vocal cords, and then spreads to the muscles of the face, neck, and 

 limbs. The scream with which ordinary epileptic attacks begin 

 probably depends on the initial excitation of this centre in 

 the cortex. 



IV. Ferrein (1741) was the first who attempted acoustic 

 experiments on the excised larynx of recently killed dogs, by 

 bringing the walls of the glottis artificially together, and blowing 

 forcibly through the trachea. 



Johannes Miiller (1839) successfully resumed the study of the 

 formation of sounds in the larynx of dead bodies. He fixed 

 threads to the two arytenoid cartilages so that he could alter 

 the width of the glottis by bringing them more or less closely 

 together, and produced different degrees of tension in the vocal 

 cords by pulling the thyroid cartilage forward by weights. 



