The ventral root (motor root) of each spinal nerve consists of axons from motor neurons whose cell bodies are found within the gray matter of the spinal cord. A ventral root and a dorsal root unite to form a spinal nerve, which passes outward from the vertebral canal through an intravertebral foramen (bone opening). A posterior branch (posterior ramus) of each spinal nerve turns toward the posteriormycontentbreak to innervate muscles and skin of the back. The main portion of the nerve, the anterior branch (anterior ramus), continues forward to supply muscles and skin on the front and sides of the trunk and limbs. The spinal nerves in the thoracic and lumbar regions have a fourth or visceral branch, which is part of the autonomic nervous system.