NERVE-CELLS OF THE SPINAL CORD 



467 



The Cells of tbe Grey Matter. — These cells are not 

 scattered uniformly throutrhout the grej' matter, but 

 arranged rather in groups. The largest cells occur in the 

 outer end of the anterior horn (see Figs. 143 and 150), 

 and since these are typical, as regards the main features 

 of their structure, of all the cells of the grey matter, we 

 may take one of them for detailed description. 



Fio. 148. — A Larok Nekve Cell from the Anterior Horn or the 

 Spin.^l Cord. 



n. Nucleus : »', small body, called the nucleolus, inside the nucle\is ; 

 p, branched processes or dendrites ; n.p, unbranched axis-cylinder 

 procesa or axon continued into the neuraxis of a motor nerve fibre. 



The body of each cell is large (varying in diameter from 

 50/x to lOOfx ; 5^0 to 2 50 of an inch), and contains a very 

 conspicuous nucleus (Fig. 148). The cell-body is pro- 

 longed into a varying number (usually many) of processes 

 called dendrites dividing and subdividing into branches, 

 which may b^ traced to some distance from the cell, be- 

 coming finer and finer, and finally ending abruptly. 

 Besides these branching processes the cell bears one 

 process, the axis-cylinder process, which does not divide 

 in this way, passes straight away from the cell and is 

 soon covered by a laj'er of myelin or a medulla ; after 

 its exit from the cord, it acquii'es additionally a neurilemma 



H H 2 



