176 SYMPATHETIC GANGLIA. [Boon i. 



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

 ganglia, consist of nerve cells and fibres imbedded in connective 

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

 them than in the spinal ganglia. As 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 may 

 have and frequently has two, three or even four or five processes ; 

 it is a multipolar cell. 



In the second place while these processes of the splanchnic 

 ganglion cell are 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, iion-medullated fibres, and remain 

 non-medullated as 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 

 seems to serve as a centre for the division of nerve fibres, and also 

 for the change from medullated to non-medullated fibres. 



In consequence of its thus possessing several processes the 

 splanchnic ganglion cell is more or less irregular and often star- 

 like in form, in contrast to the pear shape of the spinal ganglion 

 cell. But in certain situations in certain animals, for instance in 

 the frog, in many of the ganglia of the abdomen, and in the small 

 ganglia in the heart, pear-shaped splanchnic ganglion cells are met 

 with. In such cases the nucleated sheath is distinctly pear-shaped 

 or balloon-shaped, and the large conspicuous nucleus is placed, as in 

 the spinal ganglion cell, near the broad end, but the cell substance 

 of the cell is gathered at the stalk not into a single fibre but into 

 two fibres one of which is straight and the other twisted spirally 

 round the straight one. The two fibres run for some distance 

 together in the same funnel-shaped prolongation of the nucleated 

 sheath of the cell but eventually separate, each fibre acquiring a 

 sheath (sheath of Henle) of its own. Generally, if not always, one 

 fibre, usually the straight one, becomes a medullated fibre, while 



