| Definition: |
Dermal bone that is a bilaterally paired and flattened element that supports the branchiostegal membrane. Three dermal branchiostegal rays form in the branchiostegal membrane ventral to the ceratohyal cartilage. The most posterior ray, branchiostegal 3, ossifies first (3.4 mm NL), and the most anterior ray, branchiostegal 1, ossifies last (5.5 mm NL). The most posterior two branchiostegals (2 and 3) insert externally on the ceratohyal; their anterodorsal tips are thickened triangles, and the rays are expanded. The bifurcated tip of the acinaciform anteriormost ray lies at the ventral margin of the ceratohyal. |