NEUROGLIA 



141 



NEUROGLIA 



Both the gray and the white matter of the central nervous system 

 contain a peculiar supporting tissue, the neuroglia, which consists of 

 two elements, the glia cells and the glia filers. The latter are very 

 probably produced by the glia cells, of which they were formerly con- 

 sidered to be processes. They consist of a substance similar to, perhaps 

 identical with, the neurokeratin framework of myelin. 



The Glia Cells. The glia cells, as seen in Golgi preparations, are 

 divisible into two distinct types, the ependyma cells and the astrocytes. 



The EPENDYMA CELLS may 

 be considered as undifferen- 

 tiated relics of the embryonal 

 cells, from which both glia and 

 true nerve or ganglion cells 

 were developed. These cells 

 line the central canal of the 

 spinal cord and the ventricles 

 of the brain, in which latter 

 organ they also form the cover- 

 ing or outer coat of the telau 

 choroideae. 



The ependyma consists of 

 long nucleated columnar cells 

 whose free ends, in fetal and 



FIG. 154. TRANSECTIQN OF THE SPINAL CORD 

 OF A CHILD, FIFTH LUMBAR SEGMENT. 



The central H-shaped gray substance con- 

 sists of nerve cell bodies, dendrons, non-medul- 



lated portions of axons, and neurogliar sup- 

 porting tissue. The enveloping white sub- 

 stance consists of medullated axons supported 

 by neuroglia. Weigert stain. X 7. 



early life, carry a tuft of cilia ; 

 in adult life they are usually 

 non-ciliated. The attached ends 

 of these cells are embedded 



in the surrounding gelatinous tissue, and are frequently prolonged for 

 some distance as a fine branched process. In this way the ependyma of 

 the spinal cord enters into the formation of the central gelatinous sub- 

 stance, in which the branched processes of its cells ramify in a glia-like 

 manner. In the fetus the filamentous processes extend from the central 

 canal all the way to the periphery of the spinal cord. In the adult the 

 ependyma cells are prone to so multiply as to almost occlude the central 

 canal; their processes have apparently become shorter, and now reach 

 the surface of the spinal cord only at its dorsal median sulcus. 



The ASTROCYTES, when stained by the Golgi method, apparently con- 

 sist of a small cell body and an innumerable number of long slender 



