[TA] short nerves arising from the initial portion of the anterior primary rami of the thoracic and upper lumbar spinal nerves through which all presynaptic sympathetic nerve fibers must pass to reach the sympathetic trunks; also conveyed by the white rami communicantes are visceral afferent (sensory) fibers that were conveyed to the sympathetic trunks in splanchnic nerves. Most fibers conveyed by the white rami communicantes are myelinated. SYN: rami communicantes albi [TA], communicating branches of spinal nerves, rami communicantes nervorum spinalium.