chiasma

Chiasm \Chi"asm\ (k[imac]"[a^]z'm), Chiasma \Chi*as"ma\ (k[-i]*[a^]z"m[.a]), n. [NL. chiasma, fr. Gr. chi`asma two lines placed crosswise, fr. ? to mark with a [chi].] (Anat.) A commissure; an intersection or crossing of two tracts; especially, the optic commissure, or crucial union of the optic nerves. -- Chi*as"mal, a.. [1913 Webster] chiasmatic chiasmal