In Poser, the parts form a tree, and likewise in the combined tree if one model is parented to another. But sometimes I need a closed circle of parts that can adjust itself as parts are moved about. One example is a scuba diver or frogman. His breathing tube runs from somewhere on his breathing set (part of his chest) to a mouthpiece or breathing mask (part of his head). Treating the middle of the tube as part of his neck would cause hopelessly bad behavior as his head moved. What I want is to treat the tube and mask as a "tail" of segments with the curve property. but also to order that the tube segment joints must automatically move to keep his mask or mouthpiece attached to his head as his head and neck joints move.