536 ^^- I^- Andriezen, 



As follows: — 



1^*- Diffuse Network: throughout the cortex and medullary 

 substance, (with slight local or topographical variation 

 which will not here be considered). 

 2"'^- Condensation systems. 



«) Surface system — mainly derived from the „caudate" 

 neuroglia cells (see Br. Med. J. loc. cit. Fig. 1) and below 

 Fig. 7. 

 ß) Perivascular system derived from specialised varieties 

 of the stellate fibre-cells, and to some extent fi'om the 

 stellate fibre-cells as will be now detailed. 



The surface ßhre-system is shown in Fig. 7: it is a feltwork of 

 tangential fibres interlacing with one anotlier, derived mainly from the 

 caudate cells — of which 2 are shown in Fig. 7. From the cells 

 of this surface feltwork, processes or fibres stream downward into the 

 depths of the cortex, reaching to the middle of the pyramidal cell- 

 layer, and therefore over a range equivalent to half the thickness of 

 the cortex. The vessels as they dip down from the pia into the cortex 

 can also be seen to be surrounded by a number of longitudinal fibres 

 coursing in the ground substance next to the vessel wall and following 

 the vessel on its downwards path. These perivascular fibres will be 

 more fully entered upon below as they belong to the next or, 



Perivascular fibre-system. This is constituted of at least 3 diffe- 

 rent (and for convenience called) suhvarieties of stellate and elongate 

 cells which are more conspicuous around the vessels in the deeper half 

 of the cortex, and in the medullary substance. It may be mentioned 

 here that the neuroglia fibres are wholly within the brain substance, 

 being imbedded in the ground substance. They have therefore no con- 

 tinuity with connective tissue elements, which like those of the pia and 

 arachnoid are extra-cerebral, or even the vessels which although pene- 

 trating the Brain, are histologically sepai-ate from the ground substance 

 and the elements pervading the ground substance, viz nerve elements 

 and neuroglia elements. 



