1028 HISTOLOGY OF CORTEX. [BOOK in. 



Another kind of cell, the 'fusiform cell,' which is found in 

 all regions of the cortex has a characteristic spindle shape, the 

 cell-substance being prolonged at the opposite poles into tapering, 

 ultimately branched processes. The long axis of the cell is gene- 

 rally placed horizontally, following the curvature of the cortex, 

 and being thus at the sides of the sulci vertical to the surface 

 of the brain ; it is however at times inclined at various angles. 



Still another kind of cell, the 'granule cell' or 'nuclear 

 cell/ is one in which the nucleus is surrounded by a relatively 

 small quantity of cell substance, 9 //- by 7 //,, more or less spherical 

 in form in ordinary preparations, but probably breaking up into 

 delicate branched processes. Cells of this kind are sparsely scat- 

 tered throughout the cortex generally, but in particular regions, 

 e.g. the occipital, are crowded together into a layer, which in 

 many respects resembles the nuclear layer of the cerebellum, and 

 has been called the ' granular ' or ' nuclear ' layer. 



Lastly throughout the cortex are found besides indubitable 

 nerve cells and indubitable neuroglial cells, numerous small some- 

 what irregular cells, concerning which it may be debated whether 

 they are really nervous or simply neuroglial in nature. Moreover 

 in using the names given above for the various kinds of nerve cells, 

 it must be remembered that many transitional forms are observed; 

 cells for instance may be seen intermediate in form between pyra- 

 midal cells and ' fusiform ' or ' angular ' cells. 



The medullated nerve fibres which take part in the cortex may 

 be considered provisionally as forming two categories. In the 

 first place fibres sweep up vertically into the cortex from the 

 subjacent 'central white matter' taking at first a curved course 

 as they enter into the grey matter and then appearing to run 

 straight towards the surface. These are arranged in the deeper 

 levels in bundles, leaving vertical columns of the grey matter 

 between them ; but at more superficial levels the bundles spread 

 out and are gradually lost to view. Besides these distinct 

 vertical fibres and bundles of fibres, of the ordinary medullated 

 kind, which we have reason to think are the ends (or beginnings) 

 on the one hand of fibres of the pedal and tegmental systems and 

 on the other hand of fibres of the corpus callosum, or the other 

 commissural fibres spoken of as 'association' fibres ( 635), an 

 exceedingly large number of fibres of the peculiar fine medullated 

 kind run in various directions forming a dense network in the 

 ground substance of the grey matter between the cells. We may 

 add that this system of fine medullated fibres is of late growth 

 and is not fully developed in man until two or three years after 

 birth. Many of the medullated fibres, coarse as well as fine, take a 

 horizontal direction parallel to the surface, and in certain regions 

 are specially developed into a layer or into two layers so as to 

 form a horizontal streak or streaks. 



The vascular pia mater invests closely as we have said the 



