158 KERVOUS TISSUE. 



so called) not only contains fibres derived from the brain and cora, but also pro- 

 per or intrinsic fibres which take their rise in the ganglia ; and in its com- 

 munications with the spinal and cranial nerves, not only receives from these 

 nerves cerebro-siDinal fibres, but imparts to them a share of its own proper gan- 

 glionic fibres, to be incorporated in their branches and distributed peripherally 

 with them. Therefore, according to this latter view, the sympathetic nerve, 

 commonly so called, though not a mere oifset of the cerebro-spinal nerves, yet. 

 receiving as it does a share of their fibres, is not wholly independent, and for a 

 like reason the cerel^ro-spinal nerves (as commonly understood) cannot be con- 

 sidered as constituted indeiJendently of the sympathetic ; in short, both the 

 cerebro-spinal and the sympathetic are mixed nerves, that is, the branches of 

 each system consist of two sets of fibres of different and independent origin, one 

 connected centrally with the brain and cord, the other with the ganglia. Hence, 

 if we look to the central connection of their fibres as the essential ground of dis- 

 tinction among nerves, the cerebro-spinal system of nerves might, strictly speak- 

 ing, be considered as consisting of and comprehending all the fibres having their 

 centre in the cerebro-spinal axis, whether these fibres run in the nerves usually 

 denominated cerebral and spinal, or are distributed to the viscera in the branches 

 of the nerve usually named the sjonpathetic ; and, on the same ground, the syin- 

 pathetic or ganglionic sj'stem, strictly and properly so called, would consist of 

 and comprehend all the fibres connected centrally with the ganglia, wherever 

 such fibres exist and into whatever combinations they enter, whether proceeding 

 to the viscera or distributed peripherally with the nerves of the body generally ; 

 the nerve-fibres which emanate from the ganglia on the roots of the spinal and 

 cerebral nerves being reckoned into the system, as well as those from ganglia, 

 usually denominated sympathetic. Wliile ready, however, to acquiesce in the 

 justice of the above distinction, we do not mean to employ the temis already in. 

 use in a sense different from that which is currently received. 



In endeavouring to decide between the two views above stated, it may be fii'st 

 observed that the existence in the sympathetic nerve of fibres connected centrally 

 with the cerebro-spinal axis, is proved not only by tracing bundles of fibres from 

 the roots of the spinal nerves along the communicating branches and into the 

 sjnnpathetic. but by the jjain or uneasy sensations Avhich arise from disease or 

 disturbance of organs, such as the intestines, supplied exclusively, or almost 

 exclusively, by what are considered branches of the sTOipathetic ; by experiments 

 on living or recently killed animals, in which ai"tificial irritation of the roots of 

 the spinal nerves, or of various parts of the cerebro-spinal centre, caused move- 

 ments of the viscera ; and by experiments on the symi^athetic nerve in the neck, 

 by which it is sho^vn that the dilatation of the i^upil and the tonicity of the 

 cutaneous vessels of the head are dependent on fibres which i^ass along the 

 symj^athetic nerve but are centrally connected with the upper part of the spmal 

 cord and medulla oblongata. 



These facts, it is evident, accord with both of the above-mentioned opinions 

 respecting the constitution of the sjTnpathetic ; but it may be further showoi 

 that this nerve contains fibres which arise from the ganglia and take a peripheral 

 course, so that the second of the two opinions approaches nearer to the truth. 

 In support of this assertion we may adduce the actual observation of nerve-fibres 

 proceeding from the nerve-cells of the ganglia in a perij^heral du'ection only ; 

 and there are also other grounds for believing that more fibres pass out of the 

 sjnnpathetic ganglia than can possibly be derived from the brain and cord. This 

 seems to follow from a comparison of the aggregate size of the distributional 

 branches issuing from these ganglia with that of all the branches which can be 

 supposed to enter them. 



Tlie branches of communication which pass between the ganglia or gangliated 

 cord of the sympathetic and spinal nerves, are connected with the anterior and 

 greater branch of each of the latter nerves, a little in advance of the spinal 

 ganglion ; and at the point of connection the communicating Ijranch in most 

 cases divides into two portions, one central, running towards the roots of the 

 spinal nerve and the spinal cord, the other, peripheral, taking an outward course 

 along with the anterior branch of the spinal nerve with which it becomes incor- 

 porated and distributed. It can scarcely be doubted that the central portion, 



