part of develops from start stage end stage orbitosphenoid zebrafish_anatomy ZFA:0000253 orbitosphenoids TAO:0000253 Large median unpaired cartilage bone consisting of two diverging plates. Positioned medial to the eye. The orbitosphenoid develops from the Trabeculae communis and forms the anterior and anteriolateral boundary of the orbital foramen and constitutes a significant part of the sidewalls and floor of the cranial cavity. Bordered by the lateral ethmoid anteriorly, and the pterosphenoid posteriorly, The orbitosphenoid may extend ventrally to meet the parasphenoid. In the adult, the orbitosphenoid is fused ventrally to the parasphenoid via a thin sheet of bone. sphenoid region chondrocranium taenia marginalis anterior neurocranium endochondral bone palate unknown adult