STRUCTUEE OF NERVE-CELLS. 



93 



one of them is really derived from another nerve-cell elsewhere, and is 

 passing to end in a ramification which envelops the ganglion-cell ; it 

 may be coiled spirally around the issuing nerve-process as in fig. 109A. 

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

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

 109B), 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 and 

 of the brain, only one process becomes the axis-cylinder of a nerve-fibre 

 (process of Deiters), the others dividing and subdividing in a ramified 

 manner (dendrifes), until they end in an arboresence of fine twigs. 



FIG. 110. 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 large 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. 



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

 uni-, bi-, or multi-polar. 



In the ganglia the nerve-cells have a nucleated sheath (figs. 108B, 

 109) which is continuous with the sheath of the nerve-fibres with 

 which they are connected. In the spinal ganglia, and in many of 

 the ganglia at the roots of the cranial nerves, the cells are unipolar, and 

 the cell -process joins a traversing nerve-fibre by a T-shaped junction 

 (fig. 10 SB). In the sympathetic ganglia they are usually multipolar 

 (fig. 109B). The cells are disposed in aggregations of different size 



