312 THE NERVOUS SYSTEM 



the shape of the resonator through movements of the cheeks, lips 



and tongue. 



Consonants are produced by resisting the passage of au- after it 

 has passed the vocal cords. This may take place at the tip of the 

 tongue and lips (dentals), between the tongue and the hard palate 

 (labials), and at the fauces (gutturals). Explosives (?j, t, k, b, cl, g) 

 are formed by the sudden release of resistance; aspirates (/, s, I, 

 sh, V and z) by passing the air through a small slit; m and n by 

 nasal breathing. _ 



In whispering, the vocal cords do not vibrate, the sounds being 

 produced entirely in the mouth. 



The Central Mechanism of Speech 



It is probable that the development of the power of 

 speech in the human race occurs, as in each civihsed child, 

 in three stages. (1) The cry. This is used to express the 

 emotions, and in lower animals to make signs of warning. 

 The cry is probably represented centrally in the lower 

 part of the brain, since Goltz's dog, which had been 

 deprived of both cerebral hemispheres, was able to snarl, 

 bark and growl. Its doing this to friend and enemy ahke 

 showed that it was ignorant of the significance of the 

 sounds it made. (2) Vocalisation. This is the production 

 of simple vowel sounds. It is beheved to be represented 

 bilaterally in the cortex. (3) Articulation. This develops 

 with the growth of intelUgence. 



The power of speech is closely associated with the use 

 of the hands, in gestures among primitive and in gestures 

 and writing among civilised races. 



Speech is a means of forming auditory symbols, and 

 graphic records are a means of forming visual symbols 

 for objects and ideas. The child learns to talk through 

 hearing sounds. It then acquires the habit of imitating 

 these sounds, and finally it learns to associate with 

 certain visual images the sounds which others make and 

 which it copies. When the name of an object is pronounced 

 to an adult a complex mental process is set going— an audi- 

 tory image, the corresponding visual image, and memories 

 and associations connected with his past experience of the 



