418 THE NERVOUS SYSTEM 



externally applied stimuli, and is also the path of sensoiy 

 impulses to the brain. In higher animals similarly treated 

 this reflex response is less apparent, and indicates that in 

 such animals the reflex action of the cord is more depen- 

 dent upon control from higher parts of the system. 



Cerebellum. — Experiments upon the cerebellum of 

 the pigeon develop the following facts concerning this 

 organ. When all the cerebellum is removed the animal 

 can still execute voluntary movements, but these move- 

 ments instead of being definite and coordinated are sprawl- 

 ing, uncertain, and throw the animal into all sorts of 

 grotesque positions, while it is totally unable to fly. From 

 these experiments and others upon higher forms it appears 

 that while the cerebellum does not originate motor im- 

 pulses it does have the power to regulate and coordinate 

 these impulses, and is thus responsible for orderly move- 

 ment. An animal still retains sensation when the cere- 

 bellum is sliced away. 



Cerebrum. — In the cortex of the cerebral hemispheres 

 is the seat of all the psychical reactions which we include 

 under the name of intelligence, memory, will, and the 

 emotions. It is also the seat of conscious sensation, and in 

 it originate the impulses which produce voluntary move- 

 ments. Involuntary movements or reflexes may, how- 

 ever, take place when these hemispheres are removed. A 

 pigeon whose hemispheres are removed becomes a stupid, 

 drowsy creature, which, when thrown into the air, recovers 

 its equilibrium and flies, and it may even be made to feed 

 by properly applied external stimuli. If starved, how- 

 ever, it becomes restless and pecks aimlessly at the ground, 

 but does not seem to be able to locate or recognize food 

 for itself. In other words, it has lost all those responses 



