| Definition: |
The quadrate is the dorsal bone in the jaw joint with the anguloarticular of the lower jaw. Ossification of the quadrate, a cartilage bone, begins as a posteriorly projecting membranous spine between the symplectic cartilage and the preopercle (5.1 mm NL). The body of the quadrate ossifies first at the ball-and-socket articulation with the anguloarticular (6.5 mm). The adult quadrate is shaped roughly like an inverted triangle with a long, posteriorly projecting spine off its posteroventral edge. The presence of a posteroventral or posterior process of the quadrate is a synapomorphy of Teleostei.
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