TISSUES OF SPECIAL FUNCTION. 95 



1. Ganglion- or Nerve-cells (Figs. 80 and 81). Nerve-cells vary 

 greatly both in shape and size. They are rich in cytoplasm, and con- 

 tain an unusually large nucleus, generally spherical in shape, within 

 the reticulum of which there is nearly always at least one conspicu- 



FIG. 81. 



Section of unipolar nerve-cell from gray matter of spinal cord. (Flemming.) This figure 

 shows the fibrillation of the axis-cylinder process and the cytoplasm of the cell, as well 

 as the prominent chromophilic granules in the latter. 



ous nucleolus. The cell-bodies may be spherical, ovoid, polyhedral, 

 or stellate in form, and are prolonged into one or more long pro- 

 cesses. Some of these taper and branch repeatedly, the ultimate 

 delicate fibrils terminating in free extremities lying in the inter- 

 cellular substance, "dendritic processes." At least one of the 

 processes emanating from each cell is coarser than these dendritic 

 processes, and is prolonged into a nerve-fibre, forming the essen- 

 tial constituent of that structure. This process is called the 

 " axis-cylinder process." It does not branch as freely as the 

 other processes, but may give off one or more lateral twigs near 

 its origin. 



It is customary to divide the nerve-cells into unipolar, bipolar, 

 and multipolar cells, according to the number of processes proceed- 

 ing from them. The unipolar cells are connected by their single 

 processes with nerve-fibres, and many of the bipolar cells, which 

 have a fusiform shape, lie in the course of a fibre with which 

 the two processes are continuous. In such cases one of the 



