part of part of central nervous system axon tract rubroreticular tract MBA:221 UBERON:8440029 Nerve fibers that originate in the magnocellular red nucleus, cross to the other side of the midbrain, and descend in the lateral part of the brainstem tegmentum in the midbrain, and travel through the lateral funiculus of the spinal cord, coursing adjacent to the lateral corticospinal tract.