322 



SUSTENTACULAR TISSUE OF NERVE-CENTRES. 



periphery, and furnishing at" the same time the points of union between the medullated 

 and non-medullated fibres. In the uni-polar cells of the ganglia upon the posterior 

 roots of the spinal nerves, and in some other situations the single process (which 

 may be much convoluted near the cell and soon acquires a medullary sheath) 

 bifurcates after a longer or shorter course, and its two branches are eventually 

 prolonged in opposite directions along the nerve (fig. 366). 



The nerve-cells in the brain and spinal 

 cord resemble the nerve-fibres in the same 

 parts in being destitute of any nucleated 

 sheath, but in the ganglia each nerve-cell 

 is enclosed in a membranous capsule, 

 having nuclei on its inner surface and 

 apparently continuous with the nucleated 

 sheath of the nerve-fibre or fibres with 

 which the cell is connected (fig. 367). 



Susteiitacular tissue of the nerve- 

 centres ; neuroglia. In the grey matter 

 of the cerebro-spinal centre, the nerve- 

 cells appear at first sight as if imbedded 

 in a sort of matrix of granular substance, 

 interposed between them in greater or less 

 quantity, and traversed in all directions 

 by nerve-fibres. But the appearance of 



Fig. 374. STRUCTURE OF CORTEX OF CEREBELLUM (Sankey), 



a, pia mater ; 6, external layer ; c, layer of corpuscles of Purkinje ; d, inner or granule layer ; e, 

 medullary centre. 



Fig. 375. FROM A SECTION OF CEREBELLUM, STAINED BY THE METHOD OF GOLGI (Ramon y Cajal). 



The figure shows the basket-work of ramifications of the cells of the outer layer of grey matter, 

 enveloping two corpuscles of Purkinje. 



a, axis-cylinder process of one of the corpuscles ; b, basket-work of fibres derived from the axis- 

 cylinder processes, c, of cells of the outer layer. 



granular or molecular matter results from a confused interlacement of fine fibrils and 

 especially of the fine ramifications of nerve-cells, and of the special sustentacular 

 cells immediately to be described ; or from the crushing and breaking down of such 

 fibres in the process of examination. 



The supporting substance which is met with in the white matter of the brain 

 and spinal cord between the nerve-fibres also looks in section like a network T 

 although rather more open than that in the grey matter. It was supposed by 



