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Medical Definition of White rami communicantes
1. Short nerves arising from the initial portion of the ventral primary rami of the thoracic and upper lumbar spinal nerves through which all presynaptic sympathetic nerve fibres must pass to reach the sympathetic trunks; also conveyed by the white rami communicans are visceral afferent (sensory) fibres which were conveyed to the sympathetic trunks in splanchnic nerves. Most fibres conveyed by the white rami communicantes are myelinated. Synonym: rami communicantes nervorum spinalium, communicating branches of spinal nerves. (05 Mar 2000)