The necessary interaction of the conscious and subconscious mind requires a similar interaction between the corresponding systems of nerves.
According to J. Troward the beautiful method in which this interaction effected is: The cerebro-spinal system is the organ of the conscious mind and the sympathetic is the organ of the subconscious. The cerebro-spinal is the channel through which we receive conscious perception from the physical senses and exercise control over the movements of the body. This system of nerves has its center in the brain.
The Sympathetic System has its center in a ganglionic mass at the back of the stomach known as the Solar Plexus, and is the channel of that mental action which unconsciously supports the vital functions of the body.
The connection between the two systems is made by the Vagus nerve which passes out of the cerebral region as a portion of the voluntary system to the thorax, sending out branches to the heart and lungs, and finally passing through the diaphragm, it loses its outer coating and becomes identified with the nerves of the Sympathetic System, so forming a connecting link between the two and making human physically a “single entity”