chiasmatic groove chiasmatic groove the superior surface of the body of the sphenoid bone is bounded behind by a ridge, which forms the anterior border of a narrow, transverse groove, the chiasmatic groove (optic groove, prechiasmatic sulcus), above and behind which lies the optic chiasma of cranial nerve 2 (the optic nerve). chiasmatic grooveethmoid bone. upper surface. (sulcus chiasmaticus labeled at center)base of the skull. upper surface. (sphenoid bone is yellow; chiasmatic groove labeled at center left, fourth from the top of the labels near the yellow region.)detailsidentifierslatinsulcus praechiasmaticus, sulcus chiasmaticusta98a02.1.05.005ta2588fma75760anatomical terms of bone the groove ends on either side in the optic foramen, which transmits the optic nerve and ophthalmic artery into the orbital cavity. chiasmatic groove