nucleus of medulla oblongata retroambiguus nucleus neuronames:2319 retroambiguus nucleus HBA:9650 nucleus retroambiguus FMA:77096 UBERON:0016848 The term retroambiguus nucleus refers to a group of neurons in the medulla at the caudal end of the nucleus ambiguus, from which the cranial part of the accessory nerve originates ( Crosby-1962 ). nucleus retroambigualis