part of overlaps develops from start stage end stage sphenoid region pterosphenoid Paired cartilage bones, flat and hexagonal in shape that contact the orbitosphenoid anteriorly. Roofed by the frontal and bordered posteriorly by the prootic and sphenotic, the pterosphenoid bears foramina that accommodate branches of the trigeminal and facial nerves. zebrafish_anatomy pterosphenoids ZFA:0000419 TAO:0000419 chondrocranium taenia marginalis posterior endochondral bone prootic-pterosphenoid joint parasphenoid-basioccipital joint unknown adult