2/O THE NERVOUS SYSTEM 



The Speech Center. One may not be able to speak be- 

 cause he cannot control the muscles usually involved in such 

 an act, or because he has no comprehension of the meaning 

 of words, or because he is incapable of forming the idea 

 which links the reception of the impression and the muscu- 

 lar act. Aphasia is the term generally applied to inability to 

 express one's self by language. It is to be distinguished, 

 however, from aphonia, which is simply a loss of voice. 

 Ataxic aphasia is an inability to express ideas only by reason 

 of muscular incoordination ; a person so affected may use 

 words, but he cannot tell what sounds he is going to utter ; 

 his ability to receive ideas is unimpaired, and he can express 

 his own ideas in writing. When there is inability to express 

 ideas in writing, because of muscular incoordination, a con- 

 dition of agraphic aphasia is said to exist. There are also 

 cases in which a person cannot comprehend ideas expressed 

 in language and cannot express himself by either speaking 

 or writing; this is known as amnesic aphasia. It is not im- 

 possible that in some instances ideas may be received and 

 there still be an inability to express one's self in any way. 

 It is noted that when the hemiplegia accompanying the 

 aphasia is marked the form is usually ataxic ; when there is 

 no hemiplegia the aphasia is usually amnesic. 



The part of the brain presiding over speech is in the left 

 third frontal convolution near the island of Reil. In left- 

 handed persons its usual situation is almost certainly at a 

 corresponding point on the right side. Why the center is 

 unilateral has -not been explained. It may be that it was 

 originally bilateral, and the growth of the right has been 

 stopped by the superior development of the left side of the 

 brain. It is at least noticed that the right instead of the left 

 side of the brain is heavier in left-handed persons. Fibers 

 from this center (Broca's convolution) pass through the an- 

 terior part of the posterior division of the internal capsule 

 to reach the left crus, leaving which they enter the pons to 

 decussate and go to the right side of the medulla. 



