clx NERVOUS SYSTEM. 



by the pain or uneasy sensations which arise from disease or disturbance of organs, 

 such as the intestines, supplied exclusively by what are considered branches of the 

 sympathetic ; by experiments on living or recently killed animals, in which artificial 

 irritation of the roots of the spinal nerves, or of various parts of the cerebro spinal 

 centre, caused movements of the viscera; and by experiments of the sympathetic 

 nerve in the neck, by which it is shown that the dilatation of the pupil and the tonicity 

 of the cutaneous vessels of the head are dependent on fibres which pass along the 

 sympathetic nerve but 'are centrally connected with the upper part of the spinal cord. 



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

 ing the constitution of the sympathetic ; but it may be further shown 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 peripheral direction only ; and there are also other grounds for 

 believing that more fibres pass out of the sympathetic ganglia than can possibly be 

 derived from the brain and cord. This seems to follow from a comparison of the 

 aggregate size of the branches issuing from these ganglia with that of all the branches 

 which can be supposed to enter them. To explain this, however, we must first con- 

 sider the mode of communication between the sympathetic and spinal nerves. 



The branches of communication which pass between the ganglia or gangliated cord 

 of the sympathetic and the 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 branch 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 incorporated and distributed. It can 

 scarcely be doubted that the central portion, whilst it may contain fibres sent by the 

 sympathetic to the spinal nerves or to the spinal cord, must necessarily contain all 

 those which proceed from the cord to the sympathetic, and that, on the other hand, 

 the peripheral division must consist of fibres immediately proceeding from the sympa- 

 thetic and distributed peripherally with the spinal nerve. It is further observed, that 

 in some of the junctions with the spinal nerves, the central and peripheral divisions 

 of the communicating branch are about equal in size, and that in others the central 

 part is greater than the peripheral, whilst in others, again, the peripheral prevails over 

 the central. Now, in an animal such as the frog, in which the spinal nerves are of 

 small size and few in number, it is possible, with the aid of the microscope, to com- 

 pare by measurement the central and peripheral divisions of the communicating 

 branch in all the communications between the sympathetic and the spinal nerves, or 

 even to count the fibres when the branches are very fine ; and by such a comparison 

 Volkmann and Bidder have shown, that, after making all reasonable deductions and 

 allowances, the whole amount of the fibres, or at least the aggregate bulk of the 

 fasciculi, which obviously pass from the sympathetic and run outwards with the spinal 

 nerves, considerably exceeds that of the central fasciculi which must contain the fibres 

 contributed to the sympathetic from the cerebro-spinal system : and if to these peri- 

 pheral fibres we add the branches distributed to the viscera, it seems plain that more 

 fibres must proceed from the ganglia than can possibly be supposed to enter them 

 from the spinal nerves or spinal cord, and that consequently the ganglia must them- 

 selves be centres in which nerve-fibres take their rise. It is worthy of remark, that 

 in the frog, according to the observations of the anatomists just named, the central 

 division of the communicating cord greatly exceeds the peripheral in the connections 

 with the upper spinal nerves, but that lower down it gradually diminishes, absolutely 

 as well as in comparison with the peripheral, and at length disappears altogether, so 

 that the 'fasciculi connected with 'the eighth and ninth spinal nerves are entirely 

 peripheral in their course. 



Another circumstance still remains to be noticed respecting the communications of 

 the sympathetic and spinal nerves. It has been long known that in most of these 

 communications there are usually two connecting cords passing between the sympa- 

 thetic and the spinal nerve ; and it has been remarked also by various observers, that 

 these cords contain grey as well as white fasciculi. More recently, however, Todd 

 and Bowman have called attention to the fact that one of the two connecting cords is 



