It is not only at their exit that the spinal nerves thus communicate. The different cords of which each nerve is formed have precisely the same arrangement, as may be easily seen in the great trunks, as in the median, the cubital, the radial and especially the sciatic. By separating the different cords of these nerves, we see that they are not only in apposition longitudinally, but that they send numerous filaments to each other. These communications do not resemble those of the arteries, in which there is always continuity between the communicating branches. Here there is only contiguity, and each of the cords forming the nervous trunk is, as we shall see, composed of filaments; now it is these filaments that frequently go from the cord to which they belong to a neighbouring one; so that after a short distance, the cords that began the nerve are not composed of the same filaments as those that finish it; the whole becomes mingled together in the course of the nerve. Thus the cords of the branches of the brachial plexus, at its origin, are not arranged like those of the branches that terminate it. For there is this difference between the very evident plexuses formed by the nerves themselves and those that are less evident formed during their course in their interior even, viz. that in the first, it is the cords that go off and form the interlacing, and in the second it is the filaments. I once amused myself in tracing the filaments of the sciatic for a short distance; now those which composed above the external cords, were found for the most part below in the cords of the centre. This remark proves that there are not nervous cords destined to sensation and others to motion, and that if the same nerves do not serve the double use, the difference is in the filaments, and not in the cords. In the interior of the vertebral canal, in which the nervous cords are much insulated, for the want of cellular texture, the filaments that compose them do not thus communicate with each other; there is not, as without, a plexus in the interior of the nerve. This is remarked particularly at the extremity of the canal, where the nerves run a long course, as I have before said. The communication of the nerves at their exit from their osseous cavities is so general, that under this point of view it may be said that they form on every side a kind of organ every where continuous, an organ to which the optic, the olfactory, and the auditory nerves only are strangers. Besides, these kinds of communications, which are all made by juxta-position, do not appear to have much influence upon the functions of the nerves. Each of their cords, though belonging in its course to many different trunks, can perform its functions in an insulated manner; so can each filament, though concurring in its course to form many cords of the same nerve.