THE NERVOUS TISSUES. 



79 



neuroglia, a peculiar form of ectodermic tissue, .with, therefore, 

 close relations to the neurogenetic tract. Neuroglia consists of 

 extremely branched elements, or glia-cells, whose numerous pro- 

 cesses break up into 



brush-like bundles of FIG. 95. 



delicate fibrils, which A ^*^ ft 



pass in all directions 

 among the nervous ele- 

 ments, filling more or 

 less completely all inter- 

 stices. The body of the 

 glia-cells is frequently 

 stellate, possessing a nu- 

 cleus and staining in- 

 tensely with certain dyes. 

 The demonstration of 

 these neurosrlia elements 



Supporting tissues of nerve-centres : A , extensions of the 

 peripheral connective tissue of the pia mater ; B, neuroglia- 

 cells, one of which is seen in profile (s ). Golgi staining. 



is very striking in Golgi 



silver preparations, where they appear as dark, spider-like figures 

 which send out delicate fibrils in all directions. In the gray matter 

 the ground-reticulum is composed of the minutely ramifying ter- 

 minal threads of the processes of the nerve-cells, the axis-cylinders 

 of the nerve-fibres, together with the extensions of the neuroglia 

 elements. The groundwork surrounding the nerve-fibres within 

 the white matter serves the purpose of covering as well as of support, 

 and replaces the neurilemma. 



In addition to the dense reticulum formed by the neuroglia, con- 

 stituting the special sustentacular tissue of the nervous system, pro- 

 longations from the enveloping pia mater likewise penetrate within 

 the nervous masses and contribute connective-tissue trabeculae, 

 which form a supporting framework throughout the organs. These 

 connective-tissue ingrowths constitute the septa, which in many 

 places, as conspicuously in the spinal cord, separate the nervous 

 matter into distinct tracts and areas. The finer ramifications of these 

 partitions fade away in delicate extensions which mingle with the 

 fibrils of the neuroglia-cells. It is evident, therefore, that the sup- 

 porting tissue of the nervous system can no longer be regarded 

 simply as a form of connective tissue, since, in addition to the un- 

 doubted connective tissue present, the larger part is contributed by 

 the peculiar ectodermic structure, the neuroglia. 



THE STRUCTURE OF GANGLIA. 



Along the course of certain nervous cords, such as those consti- 

 tuting the sensory roots of the spinal nerves, the trunks of many of 



