44-8 



SYMPATHETIC NERVE. 



main or gangliated cord they all run in a 

 downward direction towards the pelvic ex- 



Fig. 294. 



, c 



Fibres from the root of intercostal nerve of a Rabbit. 



Towards c (in fig. 293.), the nerve chiefly con- 

 sisted of fibres similar to those indicated by B ; 

 towards b it consisted chiefly of broad fibres, A ; o 

 fibres from the communicating branch. (Mag. 250 

 diam.) 



tremity, none passing upwards towards the 

 cephalic extremity. After thus running for 

 a greater or shorter distance in the main cord, 

 they then pass off from it in the peripherical 

 branches, the point at which they leave the 

 cord being always situated lower down than 

 the point at which they entered it. This 

 arrangement was termed by him the lex pro- 

 gressns : he endeavoured to support it by 

 experiments on the niotory action of the 

 fibres contained in the sympathetic, showing 

 that when different parts of the cerebro-spinal 

 axis, as well as the rami communicantes, are 

 irritated, the contractions produced in the 

 viscera follow a certain order, which favours 



the opinion that the fibres are disposed in the 

 manner he states. This view is opposed b}' 

 Bidder and Volkmann*, on the ground that 

 it is at variance with what is actually ob- 

 served in regard to the course of these fibres 

 on joining the sympathetic. On examining 

 with the microscope the communicating 

 branch at its point of junction with the sym- 

 pathetic, they find that in so far as it consists 

 of cerebro-spinal fibres it divides into two 

 portions, one of which is directed downwards 

 in the direction of the pelvis, while the other 

 passes upwards towards the head. In small 

 animals, such as the rabbit or mouse, it is not 

 difficult, when one of the thoracic commu- 

 nicating branches is examined with the micro- 

 scope, to observe that the fibres are disposed 

 in the manner in which Volkmann and Bidder 

 describe, some passing upwards, others down- 

 wards into the main cord of the sympathetic, 

 and in which they may be traced for some 

 distance, and, according to Kolliker, into the 

 peripheral branches. That they all gradually 

 pass off from the main trunk of the sympa- 

 thetic into its peripheral branches is pro- 

 bable, as Kolliker observes, from the fact that 

 most of these contain a greater or smaller 

 number of fibres resembling those in question. 

 Peripherical Distribution. The different 

 branches of the sympathetic contain the same 

 structures as those which have been already 

 described as constituting the main trunk of 

 the nerve, viz. broader and finer tubular nerve- 

 fibres and fibres of Remak. These, however, 

 vary in the proportion in which they are pre- 

 sent in the different branches. In the whiter 

 branches of the sympathetic, such as the 

 splanchnic nerves, the number of tubular 

 nerve-fibres, as compared with the number 

 of the fibres of Remak, is much the same as 

 in the main trunk. The grayer branches, on 

 the other hand, such as the ascending or 

 carotid branches of the superior cervical gan- 

 glion, the nervi molles as well as the arterial 

 branches generally contain a large number of 

 the fibres of Remak. Many of them appear 

 to be entirely composed of these and fine 

 tubular fibres. The nerves which are distri- 

 buted to the heart are also chiefly composed 

 of fine tubular fibres and fibres of Remak. In 

 the heart of the sheep many of the branches 

 which run along the surface of the ventricles 

 are chiefly composed of the latter variety of 

 fibres, there being few tubular fibres present. 

 As already mentioned, numerous small gan- 

 glia have been described by Remak as oc- 

 curring on the cardiac nerves, both on the 

 surface and also in the substance of the organ. 

 As regards the fibres on the inner surface of 

 the heart, they cannot be distinguished by the 

 naked eye. If, however, the lining membrane 

 is dissected carefully off from the muscular 

 substance, and then, after addition of diluted 

 solution of soda, examined with a power of 

 250 diameters, they may frequently be ob- 

 served. They consist of tubular nerve-fibres 

 belonging to the finer variety, and are arranged 



* Die Selbstandegkeit, &c., p. 31. 



