The term ambiguous nucleus refers to a long narrow group of neurons embedded in the medullary reticular formation from the spinomedullary junction to the level of the inferior olivary complex. Defined by Nissl stain, it is undivided in the human ( Koutcherov-2004 ) and the mouse ( Hof-2000 ). In the macaque some authors subdivide it into three parts: a rostral compact part of the ambiguous nucleus, an intermediate subcompact part of the ambiguous nucleus and a caudal loose part of the ambiguous nucleus ( Paxinos-2009 ). In the rat it is divided into two parts: the dorsal division of the ambiguous nucleus, one of the neuroendocrine motor zone, somatic motor neuron pools, and the ventral division of the ambiguous nucleus, one of the preganglionic autonomic pools, parasympathetic component ( Swanson-2004 ).