A hinge line is an imaginary longitudinal line along the dorsal edge of the shell of a bivalve mollusk where the two valves hinge or articulate. The hinge line can easily be perceived in these images of a mussel shell and an ark shell.[1][2][3]
The hinge teeth, structures which control the articulation of the valves, are often but not always situated along the hinge line.
The hinge of a blue mussel, Mytilidae
Part of the hinge line of one valve of an ark shell, Arcidae
. This article uses material from the Wikipedia article Metasyntactic variable, which is released under the Creative Commons Attribution-ShareAlike 3.0 Unported License.