2033. As all formations have become symmetrical through and in accordance with the vascular system, so does the vegetative nervous system separate into two parallel stems which accompany the arterial trunk. They are called intercostal nerves. These ramify and form plexuses that accord with the visceral organs, which they govern. b. _Animal Nervous System._ 2034. The animal nervous system is the repetition of the vegetative, and is combined therewith to constitute an unity. The nervous cyst that was previously dissevered in a reticular manner, becomes a closed tube, which is placed upon the light-exposed side of the other animal systems, and thus upon the vertebral column. This closed nervous tube is called the _myelon_, or _spinal cord_. 2035. The spinal cord is worth as much as all the visceral nerves taken together; it is the felted system of intercostal nerves; and is, properly speaking, none other than the posterior double cord of ganglia. It consists therefore also of ganglia and plexuses, but both have coalesced, on account of the increase of the mass and its endeavour towards the attainment of union. 2036. The ganglia form a tube, which is inclosed by the tubes of the plexuses. The ganglion-tube is the gray, the plexus-tube the medullary substance. 2037. If the gray substance appear to reside within the medulla, this is the result only of involution or a folding in. The parietes of the spinal marrow stand therefore in everlasting tension with each other, like ganglia and plexuses, and like arteries and veins. 2038. The spinal marrow is the content of the bones and muscles, like the intercostal nerves or the visceral cord are the contents of the abdominal cavity, and as the blood is that of the internal and fibrous coat of the arteries. Bones and muscles are the animal parietes of the nerves, as the two vascular membranes are the vegetative walls of the blood. The skin, as branchia, incloses all, like the cellular membrane does the vessels. 2039. As the intercostal ganglia give off plexus-forming ramules; so does the spinal marrow; there are the spinal nerves. The spinal marrow is, first of all therefore, the coalescence of the two intercostal nerves. 2040. These spinal nerves are, however, animal plexuses, which partly encroach upon the visceral nerves, and partly pass to the animal systems. 2041. There are therefore two kinds of spinal nerves, vegetative and animal, and as many of them as there are divisions in the viscera and in the animal systems. 2042. The nerves pass off symmetrically from the spinal cord, because the nervous mass belongs to the symmetrical osseous system. They form therefore rings both anteriorly and posteriorly.