THE CEREBRUM. 



303 



Tangential 

 fibre-layer 



The cells of Martinotti are of small size and triangular or spindle- 

 form in outline and particularly distinguished by the unusual direction of 

 their axones. These processes pass towards the surface and within the 

 stratum zonale divide into branches, which are continued horizontally in the 

 feltwork of tangential fibres. As in other parts of the central nervous sys- 

 tem, 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, 

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

 elements, which they then support, the arrangement of the fibrillae is fairly 

 definite in certain strata. Thus with- 

 in the subpial condensation of the 

 neuroglia, the glia cells send most 

 of their processes as inwardly directed 

 brushes. The cells within the deep- 

 er 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 uniform 

 layer, but as radially disposed bun- 

 dles which gradually become less 

 distinct as 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 predominate, are 

 largely the centrally directed axones 

 of the pyramidal and the polymor- 

 phic 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 corticipetal 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 they assist in producing the tangential zone. 



Radial fibres 



FIG. 350. Section of cerebral cortex stained to 

 show nerve fibres ; the cells are not seen but lie be- 

 tween the strands of fibres. X 21. 



