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.