THE TELENCEPHALON. 



1179 



in other parts of the central nervous system, so too in the cerebral cortex there is 

 found a sprinkling of Golgi' s cells of type II. Although both dendrites and 

 axones of these cells undergo elaborate arborization, the axone is confined to a 

 limited territory in the vicinity of the cell and, therefore, never reaches the 

 stratum zonale. 



Neuroglia cells are present in all parts of the cerebral cortex and, whilst in 

 a general way they send fibrils in all directions between the nervous elements, 

 which they then support, the arrangement of the fibrillse is fairly definite in certain 

 strata. Thus within the subpial condensation of the neuroglia, the glia cells send 

 most of their processes as inwardly directed brushes. The cells within the deeper 

 part of the cortex give off their processes in two chief groups, one extending 

 towards the periphery and the other towards the white core. 



The Nerve-Fibres of the Cortex. When viewed in suitably stained sections 

 cut parallel with their general course, the cortical nerve-fibres do not appear as a uni- 

 form layer, but as radially disposed bundles which gradually become less distinct as 



FIG. 1017. 



Tangential 

 fibre-layer 



Outer stripe 

 of Baillarger 



they traverse the cortex and finally disappear 

 at about the level of the outer border of the 

 layer of large pyramidal cells. The radial 

 fibres are partly afferent and partly efferent. 

 The corticifugal components, which predomi- 

 nate, are largely the centrally directed axones 

 of the pyramidal and the polymorphic cells 

 which are continued as the axis-cylinders of 

 the fibres composing the subcortical white 

 matter. The peripherally coursing axones of 

 the cells of Martinotti also contribute to the 

 production of the fibre- radii. The cot ticipetal 

 constituents of these tracts include the nerve- 

 fibres which are derived from cells situated 

 more or less remote from the convolution in 

 which the fibres (their axones) end. Such, 

 for example, are the thalamo-cortical and the 

 tegmento-cortical fibres, as well as the many 

 commissural fibres that arise in the opposite 

 hemisphere and cross by way of the corpus 

 callosum. Although for the most part the 

 corticipetal fibres end at various levels in 

 arborizations around the pyramidal cells, some 

 are continued into the stratum zonale where, 

 breaking up into horizontal fibrillae, they assist 

 in producing the tangential zone. 



The spaces between these radial bundles 

 are occupied by a delicate interlacement, the 

 interradial felt-work, which is composed 

 in large part of the lateral and collateral 

 processes of the cells. Within the third 

 layer, the horizontally coursing collaterals 

 and processes of the large pyramidal cells 

 form a complex of unusual intricacy, which 

 condensation gives rise to the outer stripe 

 of Baillarger. Beyond the outer ends of the radial fibre-bundles, the intercel- 

 lular ground-work is occupied by a second delicate interlacement of processes 

 and collaterals, the supraradial felt-work of Edinger ; whilst immediately 

 beneath the narrow subpial neurogliar zone innumerable delicate terminal fibrillae 

 course horizontally and parallel with the surface and constitute the tangential 

 fibre-layer. The components of this layer are the terminal branches of the 

 dendrites of the pyramidal and polymorphic cells and the axones of the cells of 

 Martinotti, as well as the main and secondary processes of the fusiform elements 

 of the stratum zonale. 



Radial fibres 



Section of cerebral cortex stained to show fibres. 

 X 21. 



