(pl. rami communicans) A bundle of nerve fibers passing from one nerve to join another. – White ramus communicans – communicating ramus (containing lightly myelinated, preganglionic fibers) between a mixed spinal nerve and one of the ganglia of the sympathetic chain. – Gray ramus communicans – communicating ramus (containing unmyelinated, postganglionic fibers) between one the ganglia of the sympathetic chain and a mixed spinal nerve.