628 THE HUMAN BODY. 



.after destruction of the motor area. These facts are correl- 

 .ated with the relatively larger size of the cortical motor area 

 .and of the pyramidal tracts in monkeys as compared with dogs, 

 and the anthropoid apes as compared with other monkeys. 

 The larger and more highly organized the brain area the 

 greater the part it plays in the life-work of the animal and 

 more noticeable are the results of its absence. In man local 

 paralysis due to local cortical lesion is often only temporary: 

 this may be due to disappearance of the disease; or to the 

 primary paralysis being only a " shock " effect, and not due to 

 actual disease of the motor centre, for it is well known that 

 in animals injury to one region of the brain will often for a 

 considerable time inhibit the activity of other parts: or it may 

 be due to the hemisphere of the opposite side assuming con- 

 trol. Different observers attribute very various values to these 

 three possible factors. \ In this connection reference may be 

 made to cases of what is called aphasia, which in its fully de- 

 veloped state is a loss of the power to apply words to express 

 ideas. The power of speech may, of course, be lost through 

 disease of the larynx or paralysis of the nerves or muscles of the 

 voice organs, but such a condition is not true aphasia: the 

 aphasic person can often articulate perfectly well, but he can- 

 not attach a meaning to his spoken word : in some cases he 

 can write words with meaning, though he cannot say them; in 

 other cases (agr aphid) the power of using written words to 

 express ideas is also lost, though the person can write, and his 

 general conduct shows that he is still guided by .his intelli- 

 gence; he knows quite well what he wants to say, but he can- 

 not set the proper motor apparatus in action to utter the 

 word : if he speaks, the word has no connection with that in 

 his mind, and as soon as he hears himself speaking it he often 

 knows that the word he uses is quite wrong. We find in such 

 cases the power to understand words, and to form ideas of 

 words, and to utter words, but some link between the origin 

 of the idea and the discharge of the motor impulses willed to 

 express it is out of gear. It is as if an injured reflex centre 

 should give a wrong or inco-ordinate efferent response to an 

 afferent impulse. Aphasia is almost invariably connected 

 with disease of the area marked SP in Fig. 179 and known 

 as the third or lower frontal convolution, and the pathological 

 change is on the left side of the brain only. The area, as will 

 be seen, is closely associated with the face area and the tongue 



