The nerve-centres of the Cerebro-Spinal System are grouped closely together, while those of the Sympathetic System are scattered about the body, each organ having its appropriate centre or tiny-brain. The heart, the liver, the kidneys, the spleen, the brain, the intestinal tract, the bladder, the generative organs, have each its own particular nerve-centre of the Sympathetic System--each its tiny-brain--each, however, connected with all the others. And more than this--in addition to the tiny-brains in each of the important vital organs, there are found scattered through the trunk a number of _ganglia_, or knots of gray nervous matter, arranged longitudinally in two lines extending from just in front of the spinal column from the base of the skull to the end of the spinal column, each vertebra having its appropriate ganglia. In some cases several of these ganglia are grouped together, the number ranging from two to three. Each ganglion is a distinct centre giving off branches in four directions. There is also one place in which are grouped together several very large ganglia, forming what is known as the Solar Plexus, or Abdominal Brain, which is situated at the upper part of the abdomen, behind the stomach and in front of the aorta and the pillars of the diaphragm, and from which issue nerves extending in all directions. By some authorities the Solar Plexus is regarded as the great centre of the Sympathetic System, and the main seat of the Subconscious Mind. Dr. Byron Robinson bestowed upon this centre the name "The Abdominal Brain," saying of the use of the term: "I mean to convey the idea that it is endowed with the high powers and phenomena of a great nervous centre; that it can organize, multiply, and diminish forces." One of the most interesting and significant features of the ganglia is that of their connection with the nerve centres of the Cerebro-Spinal System, indicating the reciprocal action existing between the two great nervous systems. From each one of the ganglia in the two great lines forming the system, issues a tiny filament which connects with the spinal cord; and at the same time it receives from the spinal cord a tiny filament in return, thus establishing a double line of communication. It is held by some authorities that one of these filaments acts as a sending wire, and the other as a receiving wire between the two systems. Be this as it may, the inter-communication between the two systems is clearly indicated.