On making a section of the first cervical ganglion, previously hardened by alcohol, fibres will be perceived, which, although se parated from each other by irregular interstices filled with grey matter, are still continued uninterruptedly from une to the other ex tremity. There arc, however, besides these, other fibres, which are so complex that it is almost impossible to demonstrate their exact disposition. 1 believe, however, that, inde pendently of those fibrils which run through the ganglion, there are some which terminate in, and others which arise from the grey matter in its interior.
b. What. is the nature ty" the fibres which are connected with the ganglia? The very interesting inquiries of Brown, Darwall, Teale, Stanley, and others into the nature of those frequent affections now generally known under the term of neuralgic diseases, by which a new and unexpected light has been thrown on a most obscure branch of pathology, render this part of the present investigation of pre-eminent importance. The mutual in fluence excited by the cerebro-spinal axis and the great sympathetic on each other, in consequence of which disease of the brain and spinal chord may cause morbid actions and conditions of the organs of digestion, circulation, and secretion, and vice versa, can only be experienced by a reference to the relations which exist between these two great divisions of the nervous system. Unfortu nately, however, this question, so important both as regards physiology and pathology, is not easily resolved on account of the difficulty in the present state of our knowledge of dis tinguishing from each other the different species of fibres which enter into these organs. I shall in the first place speak of the fibres which are perceptible to the naked eye, and afterwards point out the information that has been afforded by microscopical examination.
The intervertebral ganglia (and these ob servations may be applied to those of the fifth pair, of the glosso-pharyngeal, and of the pneumo-gastric) receive fibres only from the posterior roots of the spinal nerves, which, since the researches of Bell, Magendic, and Mayo, have been regarded as being subordinate to sensation. But if the important principles announced by Dr. M. Ilall be susceptible, as I believe they are, of that confirmation from anatomical examination of which at present they stand in need, then to the true sensiferous fibrils which enter these ganglia we must add what are called by Dr. llall incident filaments.
IL is also a question which yet remains to, be decided, whether the twigs that are known to run between the posterior roots of the spinal, nerves and the sympathetic ganglions pass in reality from the former to the latter or from the latter to the former ; if, as appears most probable, these threads are furnished by the sympathetic, then it is to be presumed they are subsequently continued to the intervertebral ganglions.
With respect to the sympathetic ganglions, the following are the only facts that are at this time established.
1. There are longitudinal commissural fila ments by which the ganglia are joined to each other, and by which they are formed, however remote they may be from one another, into one great and extensive system.
2. There are fibrils which extend between the motiferons part of the cerehro-spinal axis And the sympathetic, but whether they are derived from the former or the latter is not de cided.
3. There arc sentient fibrils observing a similar disposition.
AN the anatomical facts by which these facts are established will be found under the head SYMPATHETIC NEHVE, only a few remarks are required in this place.
1. With respect to the longitudinal corn missural blues, they are as necessary here as in other parts of the nervous system ; and although Bichat speaks of this connexion of the ganglions being occasionally absent, such deficiencies are extremely rare, and if they do really exist, must be regarded as an ab normal state. The importance of this con nexion is rendered apparent by the union of the several nodules placed on the trunk of the sympathetic, which is so constant that anato mists were for a long time so far misled by it as to compare this gangliated cord with the common nerves of the body ; but it is perhaps still more striking in the commissural fibres, which are so invariably noticed passing from the sympathetic to the small ganglia of the head.
2 and 3. In consequence of the motor and sentient nerves of the head usually forming distinct trunks, the ophthalmic ganglion offers a natural analysis, as it were, of the connexion between the great sympathetic and the cerebro spinal axis. One twig passes between this small body and the nasal nerve of the fifth pair (sentient); a second extends between it and the lower division of the third pair (motor): The dissections of Arnold prove that a similar connexion exists in the spheno-palatine, the otic, and the submaxillary ganglia" Mayo has also ascertained that the branches placed between the ganglia of the great sympathetic and the compound nerves of the spine are of a twofold character, one set being attached to the sentient and the other to the motor root. The adjoining figure (fig.172), copied from a dissection I made for this purpose, shows the mode of communication in the thorax.