MICROSCOPIC STRUCTURE OF THE LAMINAE. 



87 



and a cortex of grey matter consisting of two layers, an inner and outer, the latter 

 being covered superficially by pia mater. Between the inner and outer layers of 

 grey matter is an incomplete stratum of large nerve-cells, the corpuscles of Purkinje. 

 The fibres of the white matter are medullated, and are disposed in bundles which 

 have a parallel course as they pass from the principal offshoots of the white centre 



Fig. 63. SECTION OP CORTEX OF CEREBELLUM. 

 (Sankey. ) 



a, pia mater ; b, external layer ; c, layer of 

 corpuscles of Purkinje ; d, inner or granule 

 layer ; e, medullary centre. 



of the organ into the secondary laminae. 

 This parallelism is maintained in their 

 passage through the centre of the 

 laminae, but the fibres gradually turn 

 off obliquely into the grey matter, so 

 that the white core gradually thins off 

 towards the extremities of the laminae. 

 Owing to the turning outwards and 

 passage into the grey matter of these 

 bundles of white fibres, the white core 

 is not sharply marked off under the 

 microscope from the grey cortex but 

 it is more distinctly marked off at the 

 bottom of the fissures which separate 

 the laminas than in the laminae them- 

 " selves. As the fibres pass radially into 

 the grey- matter they lose their parallel 

 arrangement, and tend to branch 

 amongst the small nerve -cells of the 

 adjacent inner layer of the grey matter ; 

 many pass through this and end in the 

 axis-cylinder processes of the cells of 

 Purkinje, whilst others pass beyond 

 these cells into the outer or " mole- 

 cular " layer of the grey matter. 



The grey matter of the cerebellar 

 cortex is disposed, as already intimated, 



in two distinct layers. The inner or granule layer is so called because it contains 

 numerous small nerve-cells known as " granules : " this layer has a reddish or 

 yellowish-brown colour in the fresh condition, hence it is sometimes termed the 

 " rust-coloured " layer. The granules are more closely packed in the outer part of 

 the layer ; near the medullary centre of the lamina they are separated by the 

 entering bundles of white fibres, between which they may penetrate for some distance 

 within the white centre. Besides small nerve-cells the granule-layer includes a few 

 glia-cells. The outer or molecular layer has, under the microscope, a finely punctated 

 (molecular) appearance. It is of fairly uniform thickness, whereas the granule-layer 

 is thicker near the extremities of the laminae than in the furrows. It contains 

 nerve-cells, but they are neither so numerous nor so small as the " granules " of the 

 inner layer, many nerve-fibres, mostly running parallel to the surface, and also a 

 number of fibres which run vertically to the surface (Bergmann's fibres), and end 

 below the pia mater. These fibres are derived from cells which are situated in the 

 granule-layer, and which are usually regarded as glia-cells (see p. 92). 



