posterior ethmoidal foramen posterior ethmoidal foramen lateral to either olfactory groove are the internal openings of the anterior and posterior ethmoidal foramina (or canals). posterior ethmoidal foramenbase of the skull. upper surface. (on the left, "posterior ethmoidal foramen" is the 9thlabel from the right.1 foramen ethmoidale, 2 canalis opticus, 3 fissura orbitalis superior, 4 fossa sacci lacrimalis, 5 sulcus infraorbitalis, 6 fissura orbitalis inferior, 7 foramen infraorbitaledetailsidentifierslatinforamen ethmoidale posteriusta98a02.1.00.080ta2485fma53136anatomical terms of bone the posterior ethmoidal foramen opens at the back part of this margin under cover of the projecting lamina of the sphenoid, and transmits the posterior ethmoidal vessels and nerve.