The fibres in the different communicating branches, as shown by Wiitzer, Midler, and others, are connected both with the anterior and posterior roots of the spinal nerves, and it seems probable that the fibres which are sent from the cerebro-spinal system are de rived from both. Volkmann #, however, as will be afterwards noticed, believes that all the fibres sent to the sympathetic are derived from the posterior root alone.
As regards the further course of the fibres which are derived by the sympathetic from the cerebro-spinal system, Valentint, holding the view that this nerve is entirely composed of such fibres, believed that on joining the main or gangliated cord they all run in a downward direction towards the pelvic ex, 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 gressus : he endeavoured to support it by experiments on the motory 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 by Bidder and Volkmann 41,, 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 Ktiilliker, 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 Milker observes, frotn 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 Rernak, 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 in bundles conttking from six to three tubes forming a widely-meshed network. The rami intestinales present much the same racters as the nerves of the heart. Many of the fibres seem to become lost in the muscular coats of the intestine; a few slender twigs, particularly in the stomach, can be traced through these to the mucous or submucous coats. The nerves of the unimpregnated uterus also contain a considerable number of the fibres of Remak. In the impregnated uterus of the cow, some of the tsNigs which run along the cervix of the organ consist almost entirely of fine tubular nerve-fibres ; in others the fibres of Remak are more numerous than the tubular nerve-fibres. Ganttlia have been observed by Remak on the nerves distributed to the mus. cular substance of the cervix uteri in the pig. Small ganglia are also present in the impreg nated cow's uterus, both on the nerves passing to the organ and also in the tvvigs which pass upwards along the posterior wall of the cervix of the uterus. Some of them contain as few as from six to nine ganglionic corpuscles: they seem to be more numerous, and are larger near the point where the cervix uteri becomes continuous with the vagina. Divi sions of the fine tubular nerve-fibres have been observed by Kilian*; he describes a fibre belonging to the finer variety as dividing into two branches, and each of these, after running a short distance, as again dividing. As regards the nerves of the urinary bladder, in that of the ox they are very numerous, especially towards the neck and posterior aspect of the organ, and present a more or less white appearance. Some run beneath the peritoneal coat, others between the deep and superficial layers of muscular fibres ; and some inay be traced through these to the mucous coat. At first the branches contain both broad and fine tubular fibres : in their farther course, only fine fibres appear to exist. There are present, especially towards the cervix of the organ, a number of small ganglia similar to those in the uterus. Ganglia have also been described by Midler as occurring on the nerves distributed to the cavernous tissue of the penis.