The Medulla Oblongata is the upper enlarged end of the spinal cord, and from it and the Cerebrum branch forth the Cranial Nerves which reach to various parts of the head, to the organs of special sense, and to some of the thoracic and abdominal organs, and to the organs of respiration.
The Spinal Cord, or spinal marrow, fills the spinal canal in the vertebral column, or "backbone." It is a long mass of nerve tissue, branching off at the several vertebrae to nerves communicating with all parts of the body.

The Spinal Cord is like a large telephone cable, and the emerging nerves are like the private wires connecting therewith.
The Sympathetic Nervous System consists of a double chain of Ganglia on the side of the Spinal column, and scattered ganglia in the head, neck, chest and abdomen.

(A ganglion is a mass of nervous matter including nerve cells.) These ganglia are connected with each other by filaments, and are also connected with the Cerebro-Spinal System by motor and sensory nerves.

From these ganglia numerous fibers branch out to the organs of the body, blood vessels, etc.

At various points, the nerves meet together and form what are known as plexuses.