This is a nonplanar mechanism. Imagine the four bar linkage on the surface of a sphere with all the rotary axes intersecting at the center of the sphere. In this model, (similar to C1), the linkage can be demounted and each of the four links can be fixed using the pedestal H2. See more about this in "Mathematics of four bar linkages".
Reference : Loeffler, Kent (Technician)Models :
