The medullary substance of the nerves is not arranged in filaments. It appears to be analogous to the white substance of the spinal marrow which is a real jelly, stagnant in the canal of the pia mater, which serves as a reservoir for it. Besides, examination proves this assertion in the optic, auditory, olfactory nerves, &c. In general I think, that this substance, as well as the cerebral, would be ranked, if they were deprived of the vessels that run through them, rather among the fluids than the solids, or they would form a medium of connexion between the two. II. _Parts common to the organization of the nervous system of animal life._ _Cellular texture._ The nerves are entirely destitute of this texture in the interior of the cranium, and the spine; but out of these they have a great quantity of it. A large external layer, first covers and then connects them with the neighbouring parts. This layer is looser than that which surrounds the arteries. Fat often accumulates in it; sometimes, though rarely it is the seat of dropsical effusions. From this common layer go off different elongations which communicate with the cellular texture of the neighbouring organs, and form a medium of union between the nerve and these organs. Within, there are other elongations that go between the nervous cords, and separate them from each other, and form for them kind of canals. When a nerve has been macerated some time in diluted nitric acid, the cords become separated from their sheath, which is to them what the layer of which we have spoken is to the whole nerve. These cellular canals often contain also fat in the great nerves, in the sciatic there is always some of it. Hence it is that when we dry these organs, there is almost always as I have observed, a fatty exhalation upon their surface; and that, when they are immersed in any alkaline solution, they have evidently an unctuous and truly saponaceous deposit. Finally new elongations going from the cellular canals that surround the cords, cover the nervous filaments with canals still smaller. Here, there is never any fat or serum, and the cellular texture has in part that peculiar nature which characterizes the sub-arterial, the sub-nervous texture, &c.; perhaps even the nervous coat is nothing but this texture considerably condensed. Besides, the cellular texture so connects the one to the other, the cords of the nerves, and the filaments of these cords, that no motion can take place there. _Blood vessels._ Each nerve receives its vessels from the surrounding trunks, which send to it branches which penetrate from all sides to the interior. The optic is an exception to this rule; the membrane that surrounds it prevents the vessels from entering it laterally. An artery passes through it in the course of its axis and sends out different branches.