CHAPTER XI 



STRUCTURE, NERVE CONNECTIONS, AND FUNCTIONS OF 

 THE CEREBRUM 



The Cerebrum in Relation to Muscular Activity. In the pre- 

 ceding chapter two classes of reflexes, spinal and cerebellar, have 

 been described. A fact it is important we should grasp, is that a 

 large part of all the activities of all animals belong to one or the 

 other of these classes. Indeed as we go down the animal scale and 

 examine such animals as fish, frogs, and turtles, it is a matter of 

 some difficulty to prove that any of their acts involve higher ner- 

 vous manifestations. In man and the higher animals, however, we 

 recognize many activities which cannot be assigned to either 

 category. Among these are all acts which we describe as volitional. 

 For the performance of these the cerebrum is essential. We will 

 get an idea of the significance of the cerebrum in relation to mus- 

 cular activity, by noting the way in which it may modify such 

 activity. 



A Normal Animal Compared with a " Reflex " One. Let us 

 imagine that we have side by side before us two living animals of 

 the same species, one normal in every respect, the other in the 

 " reflex" condition; that is, having had the cerebrum destroyed 

 but the remainder of the nervous system uninjured. Disregarding 

 for the present the phenomenon of consciousness and looking at 

 both animals simply as pieces of machinery three striking differ- 

 ences between them are manifest: 1. The "reflex" animal always 

 responds to adequate stimulation by a predictable response; 

 the intact animal sometimes responds and sometimes does not. 

 2. The "reflex" animal does not move except when stimulated, 

 while the intact animal often moves without any apparent rea- 

 son. 3. The amount of response given by the "reflex" animal 

 bears some relation to the intensity of the exciting stimulus, 

 whereas in the normal animal an apparently feeble stimulus may 

 arouse a vigorous and long-continued response. An example of 



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