RESPIRATION 



269 



are not completely blocked off, the voice assumes a nasal 

 character in pronouncing certain of the vowels ; and in some 

 languages this is the ordinary and correct pronunciation. 



Many animals have the power of emitting articulated 

 sounds ; a few have risen, like man, to the dignity of 

 sentences, but these only by imitation of the human voice. 

 Both vowels and consonants can be distinguished in the 

 notes of birds, the vocal powers of which are in general 

 higher than those of mammalian animals. The latter, as a 

 rule, produce only vowels, though some are able to form 

 consonants too. 



The nervous mechanism of voice and speech will have to be 



OU 



FIG. 96. 



FIG. 97. 



Fir,. 98. 



considered when we come to study the physiology of 

 the brain and spinal cord. But the curious physiological 

 antithesis between the functions of abduction and of adduc- 

 tion of the vocal cords may be mentioned here. The abductor 

 muscles are not employed in the production of voice; they are 

 associated with the less specialized, the less skilled and pur- 

 posive function of respiration. The adductor muscles are not 

 brought into action in respiration ; they are associated with 

 the highly-specialized function of speech. Corresponding to 

 this difference of function, we find that the adductors only 

 are represented in the cortex of the brain, the abductors in 

 the medulla oblongata. Stimulation uf an area in the lower 

 of the ascending frontal convolution, near the fissure of 



