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ELEMENTARY PHYSIOLOGY 



rabbit, the cerebrum is small in proportion to the brain as a whole, 

 and its surface is smooth. In the ape, the cerebral hemispheres 

 are proportionately larger, and their surfaces are drawn up into a 

 number of convolutions ; while in man they are large and still more 

 convoluted. We derive our knowledge of the functions of the cere- 

 brum partly from cases of injury and disease of that organ, and 

 partly from observations on the lower animals. When the cere- 

 brum is diseased or injured, the power of manifesting mental 

 faculty is more or less lost ; when the cerebrum of an animal is 

 injured, the animal is deprived of all power of voluntary move- 

 ment, and remains in a state of stupor ; it retains, however, the 

 power of performing complicated actions involuntarily. 



The cerebellum or lesser 

 brain also consists of two 

 hemispheres, each composed 

 of an external layer of grey 

 matter surrounding white 

 fibrous substance. The grey 

 matter is also convoluted, but 

 in a different manner, and 

 the pia mater dips into the 

 fissures in its surface. 



The chief function of the 

 cerebellum appears to be the 

 regulation or co-ordination of 

 all muscular movement. It 

 is the organ by which the 

 mind gains a knowledge of 

 the conditions and positions 

 of the muscles, which know- 

 Fig. i6 7 .-Section through the led S e is essential to their bar- 

 Cerebellum. monious action, especially in 



Showing the peculiar arrangement of the white and SUch Complicated movements 

 grey matter, forming what is known as the arbor as Walking and running. 

 vitce (tree of life). -ITTI i_n c 



When the cerebellum of an 



animal is injured, it can move any voluntary muscle at will, but 

 it cannot walk or fly, nor can it balance its own body, since 

 the muscles do not act with any regularity. Thus, voluntary 

 movements do not originate in the cerebellum, but only the 

 power of co-ordinating these movements. An animal retains sen- 

 sation when its cerebellum is injured, and injury to this portion 

 of the brain causes no pain. 



The medulla oblongata is a mass of white and grey matter 

 which connects the brain with the spinal cord. It is about an 

 inch in length, and is broader above where it is continuous with 



