270 THE NERVOUS SYSTEM 



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 inco- 

 ordination, a condition of a graphic aphasia is said to exist. There 

 are also cases in which a person cannot comprehend ideas ex- 

 pressed in language and cannot express himself by either speak- 

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

 impossible 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 per- 

 sons 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 develop- 

 ment 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 anterior 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. 



Functions of the Cerebrum. The superior development of 

 the intellect in man is the most predominant characteristic dis- 

 tinguishing him from the lower animals. That many such ani- 

 mals are possessed of a certain degree of intelligence is not usu- 

 ally denied; and the nature of their mental operations, though 

 they are insignificant as compared with man's, may be admitted 

 as identical with his. The most striking difference in the nervous 

 system of man as compared with that of inferior animals is 

 the large size of the cerebrum in the former. This is not sur- 



