178 SYMPATHETIC GANGLIA. [BOOK i. 



longed into a nerve fibre, one end thus being connected with the 

 posterior root and the other with the nerve trunk. In such a case 

 the nerve cell is simply a direct enlargement of the axis-cylinder, 

 with a nucleus placed in the enlargement. The nerve cells above 

 described are similar enlargements, also bearing nuclei, placed not 

 directly in the course of the axis-cylinder, but on one side and 

 connected with the axis-cylinder by the cross limb of the \- piece. 

 Hence the ordinary ganglion cell is spoken of as being unipolar, 

 those of fishes being called bipolar. The former seems to be a 

 special modification of the latter; and indeed when the de- 

 velopment of a unipolar cell is traced in the embryo it is found to 

 be bipolar at first and subsequently to become unipolar. 



In examining spinal ganglia a cell is sometimes found which 

 bears no trace of any process connecting it with a nerve fibre. 

 It is possible that such a cell, which is spoken of as apolar, 

 may be a young cell which has not yet developed its nerve process 

 or an old cell which has by degeneration lost the process which it 

 formerly possessed. 



98. The ganglia of the splanchnic system, like the spinal 

 ganglia, consist of nerve cells and nerve fibres imbedded in connective 

 tissue, which however is of a looser and less compact nature in 

 them than in the spinal ganglia. So far as the characters of their 

 nuclei, the nature of their cell-substance, and the possession of a 

 sheath are concerned what has been said concerning the nerve cells 

 of spinal ganglia holds, in general, good for those of splanchnic 

 ganglia; and indeed, in certain ganglia of the splanchnic system 

 connected with the cranial nerves, the nerve cells appear to be 

 wholly like those of spinal ganglia. In most splanchnic ganglia 

 however, in those which are generally called sympathetic ganglia, 

 two important differences may be observed between what we may 

 call the characteristic nerve cell of the splanchnic ganglion and 

 the cell of the spinal ganglion. 



In the first place, while the nerve cell of the spinal ganglia has 

 one process only, the nerve cell of the splanchnic ganglia has at 

 least two and may have three or even four or five processes ; it 

 is a bipolar or a multipolar cell. 



In the second place, while these processes of the splanchnic 

 ganglion cell may be continued on as nerve fibres, as is the single 

 process of the spinal ganglion cell, the nerve fibres so formed are, 

 in the case of most of the processes of a cell, and sometimes in 

 the case of all the processes, non-medullated fibres, and remain 

 non-medullated so far as they can be traced. In some instances 

 one process becomes at a little distance from the cell a medullated 

 fibre, while the other processes become non-medullated fibres ; and 

 we are led to believe that in this case the medullated fibre is 

 proceeding to the cell on its way from the central nervous system, 

 and that the non-medullated fibres are proceeding from the cell 

 on their way to more peripherally placed parts; the nerve cell 



