intramembranous scleral ossicle os opticus Gemminger's ossicle UBERON:0010308 os nervi optici Scleral element located at the posterior pole of the scleral cartilage surrounding the foramen through which the optic nerve fibers pass. the internal architecture of this bone reveals a cancellous marrow cavity with fatty tissue. At present, it has been documented in 219 species from 35 families, including perching birds, woodpeckers, hummingbirds, toucans, kingfishers, and falcons (Tiemeier, 1950). Morphologically, this element varies in shape from a complete encircling element in some woodpeckers (e.g., Melanerpes eryth- rocephalus) to an abbreviated arc in Gallus