1084 



THE VOICE. 



[BOOK IIL 



vous disorders, such as hysteria, are marked by failure of the 

 adductors alone, the characteristic loss of voice being due to 

 this, the first effect of structural changes in the bulb or other 

 parts of the nervous mechanism is to bring about failure of 

 the abductors $ indeed the condition of the larynx as shewn 

 by the laryngoscope may be used as an aid to the diagnosis 

 of commencing organic disease. 



672. When the larynx is used for voice the recurrent 

 laryngeals are brought into play in order to produce the essen- 

 tial condition of voice, the approximation of the vocal cords. 

 The vocal cords having been adequately approximated, low 

 notes may be uttered without any further change in the larynx ; 

 in their natural position of rest the vocal cords are sufficiently 

 tense to permit their being thrown into vibrations when brought 

 near enough together and subjected to a sufficient blast. In 

 order however to utter notes at all high, the tension of the 

 cords must be increased ; and this as we have said is brought 

 about chiefly by means of the superior laryngeal nerves and the 

 crico-thyroid muscles. Hence when these nerves are divided or 

 fail through disease, high notes can no longer be uttered ; and 

 the division or failure of the nerve even on one side only will 

 bring about this result. 



When in using the voice a change has to be made from a 

 higher to a lower note, while the action of the crico-thyroid 

 ceases or is lowered, that of the antagonistic thyro-arytenoid 

 comes into play, and the recurrent laryngeal nerve is again 

 used. 



673. Utterance of the voice is a conspicuously voluntary 

 act and in the vast majority of cases an eminently skilled act. 

 Hence we find, as we have already ( 484 488) seen, an area in 

 the motor region of the cerebral cortex devoted to phonation. 

 This in the monkey (Fig. 123) lies at the lowest part of the as- 

 cending frontal convolution wedged in between the sylvian 

 fissure and the lower end of the precentral fissure ; in man as 

 we have seen (Fig. 136) the more highly developed area for 

 4 speech' is situate at the posterior end of the third frontal 

 convolution, having as we have also seen an importance on 

 the left side of the brain which it does not possess on the 

 right. 



Stimulation of the area in question in the monkey or of the 

 corresponding area in the dog leads to adduction of the cords 

 and closure of the glottis, the resulting movement being bi- 

 lateral. As in the case of other areas, the effect is more 

 pure, the laryngeal movement is less mixed with other move- 

 ments, when the stimulation is strictly limited to a certain 

 part of the whole area, in this case to the lower part. But 

 stimulation of the cortex near the pure centre for phonation 

 leads to an acceleration in the rhythm of and exaggeration of 



