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NERVOUS SYSTEM 



neurons. The neuron is composed of (i) a cell-body, (2) a neurite, 

 formerly known as the axis-cylinder prolongation, (3) dendrites, formerly 

 called protoplas- 

 mic prolongations 

 and (4) collaterals, 

 given off by the neurites. The 

 neurites are fibrillated, and 

 their terminal fibrils are called 

 teloneurites. In their course 

 they frequently give off large 

 numbers of collaterals. The 

 terminal fibrils of the dendrites 

 are called telodendrites. The 

 cell-body is identical with what 

 has already been described as 

 the nerve-cell. The unstained 

 Fig. 1 10 shows the cell-body, 

 the neurite and the protoplas- 

 mic prolongations, but not the 



Fig. in. Nerve-cells, glia-cells and neuroglia, 

 from the spinal cord of the calf (Lavdowsky). 



collaterals, teloneurites and en< neurites . the neurite from the lower cell gives off a 



telodendrites. It is Supposed process. The arborescent processes are dendrites branch- 

 , , . , . ing among the fibres of neuroglia. 



that nerve-impulses are sent 



out by the cell-body through the neurites and that impressions are received 



by the dendrites. 



Accessory Anatomical Elements of 

 the Nerve-centres. In addition to the 

 neurons, which probably are the only 

 structures directly concerned in in- 

 nervation, are the following accessory 

 anatomical elements : I, outer cover- 

 ings surrounding some of the cells ; 



2, intercellular granular matter ; 



3, peculiar corpuscles called myelo- 

 cytes (Robin); 4, connective-tissue 

 elements ; 5, neuroglia ; 6, bloodves- 

 sels and lymphatics. 



Certain of the cells in the spinal 

 ganglia and in the ganglia of the 

 sympathetic system are surrounded 

 with a covering, removed a certain 

 distance from the cell itself so as to 

 be nearly twice the diameter of the 



Fig. 112. Diagram of a nerve-cell to show the 

 Nissl granules (R. y Cajal). 



<z, axis-cylinder process ; b, Nissl granules ; 

 c, achromatic substance between them ; d, nu- 

 cleus ; e, dendrite with Nissl granule at division. 



