  We investigate the motions of a bar structure consisting of two congruent
tetrahedra, whose edges in their basic position form the face diagonals of a
rectangular parallelepiped. The constraint of the motion is that the originally
intersecting edges should remain coplanar. We determine all finite motions of
our bar structure. This generalizes our earlier work, where we did the same for
the case when the rectangular parallelepiped was a cube. At the end of the
paper we point out three further possibilities to generalize the question about
the cube, and give for them examples of finite motions.
