The term medial part of the medial mammillary nucleus refers to the more medial of two parts of the medial mammillary nucleus in the human ( Saper-2004 ), the macaque ( Paxinos-2009a ), the rat ( Paxinos-2009b ), and the mouse ( Franklin-2008 ). In the human it is considerably larger than the lateral part of the medial mammillary nucleus from which it is separated by fibers of the fornix ( Saper-2004 ). In the macaque, rat, and mouse the medial and lateral parts are more equal in size. Some authors do not divide the medial mammillary nucleus of the rat ( Swanson-2004 ) and mouse ( Hof-2000 ) into medial and lateral parts. The combination is equivalent to the body of the medial mammillary nucleus in their parcellation. Functionally the medial mammillary nucleus is part of the behavior control column of the brainstem motor system ( Swanson-2004 ).