CEREBELLUM. 293 



also networks of medullated nerve fibres. A part of these fibres 

 run at right angles, while others lie parallel to the surface. Among 

 ihe former are the axones derived from the pyramidal cells, 

 as well as those fibres proceeding to the cortex from lower down 

 in the central nervous system. These fibres run in bundles 

 through the third arid fourth layers up to the layer of small 

 pyramidal cells. They form the so-called radial bundles. 

 The strands of fibres running parallel to the surface are de- 

 rived from many sources. The outermost forming the tangen- 

 tial fibres, and those contained in the small pyramidal cell 

 layer, as well as those belonging to the so-called supraradial 

 network, represent largely the side branches of fibres running 

 from below up to the brain surface. 



The deeper fibres cross the radial bundles and form the 

 .so-called interradial bundles. Some of these run in the large 

 pyramidal cell layers, and form there the horizontal fibre tracts 

 of Gennari or Bail larger. The fibres of the interradial network 

 are formed from collaterals of axones of the pyramidal cells. 



The neuroglia distributed unequally in the different layers 

 of the brain consists of two elements, the glia cells and glia 

 fibres. By means of the Golgi method the following forms 

 of glia cells have been made out : short-rayed cells (Fig. 219, 

 G1 2 ), which lie in the gray matter and possess much-branched 

 processes ; long-rayed cells (G1 3 ), which lie mainly in the white 

 matter and possess fine processes branched only slightly ; and 

 arborescent cells (Gli), which lie at the surface of the cortex 

 and send their processes outward. 



Weigert's method which gives a special differentiation to the 

 glia fibres, shows in the outer layer of the cortex a thick corti- 

 cal sheath, composed of a rich tangentically placed plexus of 

 glia fibres In the deeper layers of the cortex the glia fibres 

 are not so abundant, while in the medullary substance they 

 form again a, dense network. 



D. Cerebellum. 



The layers of the cerebellum are marked off much more 

 sharply from one another than those of the cerebrum (Figs. 



