STRUCTURE OF NERVE-CELLS 



77 



from the cell, which is thus rendered somewhat spindle-shaped, but 

 occasionally they emerge at the same part, and the cell, being tapered 

 in their direction, becomes pyriform (fig. 92). In these cases one fibre 

 often coils spirally round the other (fig. 92, b) before they separate to 

 proceed in opposite directions as the axis-cylinders of nerve-fibres. 

 When there are three or more processes, the cell becomes irregularly 

 angular or stellate. Sometimes, as in the sympathetic ganglia (fig. 93), 

 all the processes appear to become nerve-fibres, but in other instances, 

 as in the large cells of the grey matter of the spinal cord, only one 



FIG. 94. NERVE-CELL FROM SPINAL CORD OF ox, ISOLATED AFTER MACERATION 

 IN VERY DILUTE CHROMIC ACID. (Magnified 175 diameters.) 



The cell has a well-defined, clear, round nucleus, and a bright nucleolus. The cell processes 

 are seen to be finely fibrillated, the fibrils passing from one process into another through 

 the body of the cell. , axis-cylinder process broken a short distance from the cell. 



process becomes the axis-cylinder of a nerve-fibre (process of Deiters), 

 the others dividing and subdividing in a ramified manner until their 

 further course can no longer be traced. Their ultimate branches 

 appear to lose themselves in a network which pervades the whole of 

 the grey matter. 



According to the number of their processes, nerve-cells are termed 

 uni-, bi-, or multi-polar. 



Many nerve- cells, and notably those of the spinal cord, have a finely 

 fibrillar structure. The fibrils can be traced into the branches of the 

 cells and into the axis-cylinders of nerve-fibres which are connected 

 with the cells (fig. 95). Otherwise the cells have a finely granular 

 appearance ; often with a clump of black, brown, or yellow pigment- 

 granules placed at one side of the nucleus. 



