part of adult optic lobe optic chiasma OCH optic chiasm FBbt:00003921 The projection of axons between the lamina and medulla (first optic chiasma) or between the medulla and lobula (second optic chiasma). The linear order of axons along each horizontal row of retinotopic cartridges or columns is reversed by the chiasma. VFB:FBbt_00003921 fly_anatomy.ontology chiasma