so 



that ths cerebellum bec^ime establishe'i in its ors^inization 

 quite early in the history of vertebrates. 



Undoubtedly, the key to the significaace of cerebellar 

 structure and physiology is to be looked for in the neurones 

 of PurkiTje. These striking cells, with their characteristic 

 tree-like tops, apparently have all of the other structural 

 elements present arranged contributory to them. Imbedded in 

 the midst of the nervous matter, supported by the interlacing 

 processes of the neuroglia there, a Purkinje neurone sends its 

 great branching dendrites outward into a veritable maze of 

 possible physiological connections, for such the molecular 

 layer really proves to be. We have seen that the granular 

 neurones contribute their axones to a series of fibres passing 

 horizontally through a row of spreading Purkinje dendrites; 

 that the neurones of the molecular layer are themselves radi- 

 ately connecting paths; and, finally, that the incoming nerve- 

 fibres, those arising outside the cerebellum, end, some in the 

 granular layer, others taking a longer course into the molec- 

 ular layer. These several elements evidently have no other 

 purpose than the bringing of all incoming impressions, through 

 one path or another, to bear upon the neurones of Purkinje. 

 The great spreading top of a Purkinje cell is obviously a de- 

 vice for providing a large receptive surface for such impres- 

 sions, thile the many thorn-like gemmules with which the den- 

 drites are stadded serve as a greater extension still of that 

 surface, or, perhaps, make one which is more readily impressed. 



