The relations of size of the nervous system with the brain are in man and most quadrupeds, in an inverse proportion, as has been observed by Soemmering. In man the brain is much more voluminous than in the others, who have nerves larger than his. It is easy to prove this assertion, in all the animals that we commonly employ for our experiments; in fact, small dogs are used, on account of the size of their nerves in very delicate experiments upon sensibility. This difference is a striking proof of the superiority of man, as it respects the intellectual phenomena, which are all referable to the encephalic mass. On the other hand, many animals are superior to him as it respects motions and the four senses of taste, of smell, of hearing and seeing. Observe however that he surpasses them all in the perfection of the fifth sense, viz. that of touch. Why? Because this sense is entirely different from the others, is consequent to them, and corrects their errors. We touch, because we have seen, heard, tasted and smelt. This sense is voluntary; it supposes reflection in the animal that exercises it, the others do not. Light, sounds, &c. strike the respective organs without any effort of the animal; but he touches nothing without a preliminary act of the intellectual functions. It is not then astonishing, that the perfection of the organs of touch and the great development of the brain, should be in man, in the same proportion, and that in those animals, in whom the brain is more contracted, the touch should be more obtuse and the organs less perfect. ARTICLE FIRST. EXTERNAL FORMS OF THE NERVOUS SYSTEM OF ANIMAL LIFE. I shall consider these forms, 1st. in the origin; 2d. in the course; 3d. in the termination of the cerebral nerves. I. _Origin of the cerebral nerves._ The word origin should only be understood in relation to anatomical arrangement. In fact, the nerves are formed at the same time as the brain; they are rather organs of communication with this viscus, than elongations of it. If we take a view of the functions of one part of the nervous system, we shall see that the termination is at the brain, and the origin is upon the surface. Is it not said that the nerves go towards this or that part, that the arteries take this course, wind about, &c.? These are only metaphorical expressions, the least reflection will determine their meaning.