THE NERVOUS SYSTEM 323 



muscle-fibres at a considerable distance. Small cells could 

 not do the work. Precisely similar reasons can be given for 

 the large size of the cells of Purkinje in the cerebellum, which 

 transmit the elaborated product, as we may term it, of this 

 organ to the great brain ; and for the dimensions of the large 

 pyramids of the great brain, which convey its decisions to 

 the spinal cord. The small pyramids of the cortex of the great 

 brain distribute the first crude impressions of sensations to 

 neighbouring (association) areas of the cortex. A cell of 

 Purkinje (Fig. 23) has a more complicated, and at the same time 

 a more regular, form than any other nerve-cell. It resembles 

 an exceedingly richly branched espalier pear-tree, set at right 

 angles to the narrow convolutions of the cerebellum ; a dispo- 

 sition easily accounted for, when the structure of the cortex of 

 this organ is considered. Its outer layer in which the espalier 

 processes ramify is traversed longitudinally by an infinity of 

 nerve-threads, the bifurcated axons of granules. These granules 

 are small neurones which take up impulses from afferent 

 (" mossy ") fibres, and distribute them to the dendrites of 

 the Purkinje cells each collecting from a few fibrils only 

 of the sensory channels. (The word " sensory " is used to 

 indicate that sense-organs are their provenance, and not that 

 their messages become sensations.) The numerous spreading 

 branches of a Purkinje cell, disposed in a transverse plane, are 

 obviously arranged to hold up and keep apart these myriads 

 of longitudinal threads. A cerebral pyramid is shaped like a 

 fir-tree. It is placed in a definitely stratified layer. By its 

 branches it collects impulses from the superficial strata, which 

 it transmits through its stem to the white matter beneath the 

 cortex. The various parts of the central nervous system have 

 work of different kinds to do, and we find interposed in the 

 circuits which compose the several parts cells of various types. 

 We speak of the large cells as " motor," the granules as " sen- 

 sory," the small pyramids as " association " cells such terms 

 indicating the positions which they occupy in the arcs, but not 

 defining their functions. Of specialization of function the 

 physiologist cannot obtain a hint. He cannot classify nerve-cells 

 in groups concerned in reflex action, in feeling, in remembering, 

 in willing, in thought. On the contrary, he can assert with 

 confidence that such distinctions are not to be drawn. 



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