These nerves differ from those last described, in the fact that each of them arises from the side of the spinal cord by two roots - one sensitive, the other motor. The sensitive root is the upper one and has upon it a ganglion. The motor root is the one below. They pass out of the spinal canal together through the intervertebral opening, and then the two roots join their fibres to form a compound nerve, a nerve having motor and sentient properties. Each spinal nerve now divides into a superior and inferior division, and from the latter sends a branch to the sympathetic.