It follows from this, that the regeneration of the nerves, which has lately been the object of much research, and which Cruikshank, Monro, &c. have particularly demonstrated, has nothing peculiar in it; that it is only a consequence of the general laws of cicatrization, and a proof of the constant uniformity of the operations of nature, though these operations present at first sight different results. A nerve, that is cut out in its whole course, is never reproduced like a nail, or the hair, which take a length, form, and appearance exactly the same as they had before they were removed. It is under the point of view that we have presented them, and not under this last, that the nervous reproductions should be described. ARTICLE FOURTH. DEVELOPMENT OF THE NERVOUS SYSTEM OF ANIMAL LIFE. I. _State of this system in the Fœtus._ The nervous system of animal life is one of the first that is developed. If the heart is the first that has motion, the brain is the first that has any considerable size. The disproportion of the head to the other parts is remarkable in the first periods after conception; its size is monstrous when compared with that of the subsequent ages. Now it is evident, that it is the brain that produces this, and that the increase of the size of the bones and the membranes that surround it, is owing to it. We may say that by creating first the heart and the brain, and developing them much sooner than the other organs, nature wished first to establish the foundations of the organization of the two lives. For on the one hand, it is the brain which is the centre of animal life; it is to this that all the sensations are referred; it is from it that all the voluntary motions proceed. On the other hand, by sending the blood towards all the organs, the heart evidently presides over the circulation, the secretions, exhalations, nutrition, &c. which compose by their union organic life. When these two essential bases exist, nature begins to build, or rather develop around them the double organized edifice, which produces on the one part a communication between the animal and external bodies, and on the other nourishes it.