PARTS OF THE NERVOUS SYSTEM 



433 



fibers, the pons, which run around into the lower part of the brain 

 or medulla oblongata. The medulla is the enlarged beginning of 

 the spinal cord, and is made up largely of fibers running longi- 

 tudinally. 



Functions of parts of the central nervous system of the frog. 

 From studies of lower animals scientists have learned about the 

 functions of various parts of the central nervous system in man. 



It has been found that if the entire brain of a frog is destroyed 

 or separated from the spinal cord, the frog will continue to live. 

 It will not move or croak, but if acid is placed upon the skin the 

 legs will make movements to push away and to clean off the irritat- 

 ing substance. The spinal cord is thus shown to be a center of 

 defensive movements. If the cerebrum is separated from the 

 rest of the nervous system, the frog seems to act a little differently 

 from the normal animal It jumps when touched, and swims when 

 placed in water. It will croak when stroked, or swallow if food 

 is placed in its mouth. But it manifests neither hunger nor fear, 

 and is in every sense a machine which will perform certain actions 

 after certain stimulations. Its movements are automatic. The 

 cerebellum and medulla then must be the centers of muscular 

 coordination and automatic or involuntary movements. If we 



olfactory.! ; 

 lobes tef 



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 medulla K 



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 cord 



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 medulla} 



spinal 

 Cord 



....... olfactory lobes.. 



cerebral lobes.. 



optic. 

 lobes 

 medulla 



cerefcell 



■medulla- 



Spinal cow- rjf spinal cord 



Brains of a perch, frog, alligator, pigeon, and cat. Can you tell, from diagrams, why a cat has 

 more intelligence than a pigeon or a fish ? 



watch the movements of a frog which has the brain uninjured in any- 

 way, we find that it acts spontaneously. It tries to escape when 

 caught. It feels hungry and seeks food. It acts like a normal frog 

 This shows that the cerebrum is the center of all voluntary activities. 



