Commissure : When a white matter tract crosses the median plane (Henle, 1855) in animals with bilateral symmetry and then assumes a transverse course, the crossing segment is called a commissure. Generally, a commissure forms connections between the same or nearby gray matter regions on the right and left sides. The term was used in this sense as long ago as Willis (1664, see translation by Pordage, 1681, p. 159). Also see Nauta & Feirtag (1986, p. 82, note).