Note 17 — Chapter VI · GENERAL DIFFERENCES OF THE TWO LIVES WITH RESPECT TO MENTAL AFFECTION.

Note by the Author.—This nervous network, going principally from the semi-lunar ganglion, belongs to almost the whole abdominal vascular system, whose various ramifications it follows. It is, according to the usual manner of considering it, one of the divisions of the great sympathetic; but it seems to me that the ideas of anatomists respecting this important nerve are not conformable to nature.

Every one considers it as a medullary cord, extending from the head to the sacrum, sending in its course various ramifications to the neck, the thorax and the abdomen, following in its distributions a course analogous to those nerves of the spine, and deriving its origin from those nerves, according to some, and from those of the brain, according to others. Whatever be the name by which it is designated, sympathetic, intercostal, &c.; the manner of describing it is always the same.

I believe that this manner is altogether wrong, that there really exists no nerve analogous to the one designated by these words, and that what is taken for a nerve is only a series of communications between different nervous centres, placed at different distances from each other.

These nervous centres are the ganglions, scattered throughout the different regions, they have all an independent and insulated action. Each is a particular centre which sends in various directions many ramifications, which carry to their respective organs the irradiations of the centre from which they go off. Among these ramifications, some go from one ganglion to another; and as these branches which unite the ganglions form by their union a kind of continuous cord, this has been considered as a distinct nerve; but these branches are only communications, simple anastomoses, and not a nerve analogous to the others.

This is so true, that these communications are often interrupted. There are subjects, for example, in whom is found a very distinct interval between the pectoral and lumbar portions of what is called the great sympathetic, which seems to be cut off in this place. I have seen this pretended nerve cease and afterwards reappear, either in the lumbar or sacral region. Who does not know that sometimes a single branch, sometimes many go from one ganglion to another, especially between the last cervical and the first dorsal; that the size of these branches varies remarkably; and that after having furnished many divisions, the sympathetic is larger than before it gave off any?

These considerations evidently prove that the communicating branches of the ganglions no more suppose a continuous nerve than the branches which go from each of the cervical, lumbar or sacral pair to the two pair which are superior and inferior to them. In fact, notwithstanding these communications, we consider each pair in a separate manner, and do not regard their union as a nerve.

It is necessary to describe in the same way separately each ganglion, and the branches which go off from it.

Hence I shall divide hereafter in my descriptions, in which I have hitherto pursued the ordinary course, the nerves into two great systems, one arising from the brain, and the other from the ganglions; the first has a single centre, the second has a great number of them.

I shall first examine the divisions of the cerebral system; I shall afterwards treat of the system of the ganglions, which may be subdivided into those of the head, the neck, the thorax, the abdomen and the pelvis.

In the head is found the lenticular ganglion, that of Meckel, that of the sublingual gland, &c. &c. Though no communication connects these different centres, either together or with the pretended great sympathetic, yet their description belongs to that of the nerves of which this is the connecting link, as the communications are arrangements merely accidental to this system of nerves.

In the neck there are the three cervical ganglions, sometimes another upon the side of the trachea, in the thorax the twelve thoracic, in the abdomen the semi-lunar, the lumbar, &c. and in the pelvis the sacral; these are the different centres whose ramifications it is necessary to examine separately, as we do those of the cerebral centre.

For example, I shall first describe the semi-lunar ganglion, as we do the brain; then I shall examine the branches, among which, is that by which it communicates with the thoracic ganglions, that is to say, the great splanchnic; for it is very incorrect to consider this nerve as giving origin to the ganglion. In the same way, in the neck and the head, each ganglion will be first described; then I shall treat of its branches, among which are those of communications. The arrangement being nearly the same for the ganglions of the thorax, the pelvis and the loins, the description of each region will be similar.

This manner of describing the nerves, by placing an evident line of demarcation between the two systems, exhibits these two systems such as they really are in nature.

What anatomist, in fact, has not been struck with the differences that exist between the nerves of these two systems? Those of the brain are larger, less numerous, whiter, more compact in their texture and exhibit less variety. On the contrary, the extreme tenuity, great number, especially towards the plexuses, greyish colour, remarkable softness of texture and varieties extremely common are characters of the nerves coming from the ganglions, if we except those of communication with the cerebral nerves and some of those which unite together these small nervous centres.

Besides, this division of the general system of the nerves into two secondary ones, accords very well with that of life. We know in fact that the external functions, the sensations, locomotion and the voice are all dependent on the cerebral nervous system; that on the contrary, most of the organs which perform the internal functions derive from the ganglions their nerves, and with them the principle of their action. We know that animal sensibility and contractility arise from the first, and that where the second alone are found, there is only organic sensibility and contractility.

I have said that the termination of this kind of sensibility and the origin of the corresponding contractility are in the organ in which they are noticed; but perhaps both the termination and origin are more remote, and are in the ganglion from which the organ receives its nerves, as the termination of animal sensibility and the origin of the contractility of the same species are always in the brain. If it be so, as the ganglions are very numerous, we can understand why the forces of organic life do not refer, like those of animal life, to a common centre.

It is evident from these considerations, that there is no great sympathetic nerve, and that what has been designated by this word is only an assemblage of small nervous systems, with distinct functions, but with communicating branches.

We see then what should be thought of the disputes of anatomists respecting the origin of this pretended nerve, placed in the fifth, sixth pair, &c. in those of the neck, back, &c.

Many physiologists have entertained concerning the ganglions opinions similar to those which I have now offered, by considering these bodies as small brains; but it is essential that these opinions should enter into the description, which, as it is now made, gives a very inaccurate idea both of these nervous centres and of the nerves which go off from them.

The expression of nervous branches giving origin to such or such a ganglion, &c. resembles that in which we should consider the brain as arising from the nerves of which it is itself the origin.