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A TEXTBOOK OF PHYSIOLOGY 



1. Hear the noise The receiving mechanism. 



2. Appreciate the meaning of the noise (the words) 



3. Associate it with former stored impressions 



4. By judgment formulate the answer 



5. Clothe the answer in words 



6. Associate this answer with the motor centres 

 concerned in the activation of the muscles taking part 

 in the production of speech movements lips, tongue, 

 Jarynx, etc. } 



1. Send impulses down the efferent tracts to the nerves to 

 these parts, and cause the muscles to functionate The discharging 

 mechanism. 



The 



association 

 mechanism. 



JIG. 445. DIAGRAM OF LKFT CEREBKAL HEMISPHERE, SHOWING APPROXIMATE 

 POSITIONS OF THE CENTRES CONCERNED IN SPEECH. (From Purves Stewart's 

 "Diagnosis of Nervous Diseases.") 



Similarly, a great number of processes are concerned in the appre- 

 ciation of written words and in the power to express the answer in 

 writing. It was at one time believed that a certain part of the brain, 

 known as Broca's area, was especially concerned, as the special co- 

 ordinating centre, in speech. This area is unilateral, and is situated 

 in a right-handed person in the left inferior frontal convolution. It 

 is undoubtedly in intimate connection with the neighbouring motor 

 areas concerned in the movements of the tongue, lips, and larynx, 

 but it has been shown that it may be diseased without any disorder 

 of speech (aphasia) resulting. The cases of " motor " aphasia, which 

 were said to be the result of a lesion of Broca's area, are now said to 

 be due to a lesion of the lenticular nucleus, and to a varying extent 

 of an area known as Wernicko's area. The former lesion involves 

 the external capsule, and possibly the anterior part of the internal 

 capsule, and causes an inability to articulate (anarthria). 



Wernicke's area is situated in the supramarginal and angular 

 gyri, comprising the " visual word centre," and in the posterior part 

 of the superior temporal sphenoidal lobe, comprising the " auditory 

 word centre." A lesion of the area results in " sensory aphasia," 



