Small, I think that the picture in your post comes from Pro Pack or Poser 5, I mostly use use Poser 4, which does not provide this graphic display of the "bones". But back here in the stone age I think that this line represents a parent/child relationship between actors (body parts). In a cr2 this relationship is defined in the 'figure' section of the cr2, and would look look somthing like the graphic above (where the blue line represents data that has left out for reasons of space).

As to how you create this parent/child relationship, it could be set up in the PHI file, or you could enter it by hand in the cr2 using a text editor (there may be other ways that I haven't thought of).