THE CEREBELLUM 605 



The cerebellum through this system of efferent and afferent fibers is 

 Bought into relation with many different regions of the cerebrum, pons, 

 [edulla, and spinal cord. Each half of the cerebellum is connected with the 

 [regoing structures of the same side, and of the opposite side. 



THE FUNCTIONS OF THE CEREBELLUM. 



! From the observations of the results of experimental lesions, from the 

 Jialysis of clinico-pathologic facts, and from the comparative anatomic 

 bvelopment in different animals, the deduction has been drawn that the 

 trebellum coordinates and harmonizes the action of those muscles the 

 i:tivities of which are necessary to the maintenance of body equilibrium 

 oth during station and progression. 



By equilibrium of the body is understood a condition which may be main- 

 lined for a variable length of time without displacement, and is possible only 

 i) long as a vertical line passing through the center of gravity falls within the 

 [ase of support. The support offered by the earth to the feet neutralizes and 

 [imnteracts the force of gravity. In standing, when the body is in the erect or 

 hilitary position, the arms by the side, the center of gravity lies between the 

 Ficrum and the last lumbar vertebra, and the line of gravity falls between the 

 [;et and within the base of support. The entire skeleton for the time being 

 I rendered .fixed and rigid at all its joints by the combined action of the 

 mscles connected with it. That this position may be maintained all the 

 ifferent groups of antagonistic but cooperative muscles must be accurately 

 Dordinated in their actions. Any failure in this respect is at once attended 

 y a disturbance of the equilibrium and displacement. 



In progression, walking, running, dancing, etc., the body is translated 

 rom point to point by the alternate action of the legs. Whether the direction 

 f the translation be rectilinear or curvilinear, as the legs change their position 

 :om moment to moment, the center of gravity also changes, and at once the 

 quilibrium is menaced. If it is to be maintained and displacement prevente 

 Here must be a prompt readjustment in the relation of all parts of the 

 lody so that the line of gravity falls again within the base of support. 

 nore complicated the moments of progression, or the 'narrower the base ot 

 upport, the greater is the danger to the equilibrium, and hence the necessity 

 br rapid and compensatory changes in coordinated muscle activity. All 

 movements of this character, in man at least, are primarily volitional and 

 lequire for their performance the constant exercise of the attention. With 

 requent repetition they gradually come to be performed independently c 

 oSciousness and fall info the category of secondary or acquired reflexes. 



Though coordinating power is exhibited by the spinal cord, med 

 aid basal ganglia, it is only in the cerebellum that this power attains it 

 highest development and differentiation. To it is assigned the power 

 Defecting and grouping muscles, not in any restricted P^.^^f^ 

 ,he body, and coordinating their actions in such a manner as to pr( 



iqU The Results of Experimental Lesions.-If the cerebellum in its totality 

 Coordinates and harmonizes the action of the muscles on the 





