One key point to note is that the BackJoint and Spine bodyparts are not physically connected - it is just the maths that keeps them together. In my early attempts it kept breaking apart because I'd made mistakes in the maths !

If you look at the Hierarchy Editor you'll see that the Book bodypart (which has no physical mesh attached to it - it's just a dummy) has three direct children: PageBlock4; BackCover; and BackJoint. The rest of the PageBlocks, the FrontCover, FrontJoint, and Spine are in a chain under PageBlock4

(I'm not sure why the FrontCover bone doesn't show up in the image above - I think it's similar to the BackCover bone)

This shows in principle how it's possible, using just valueOps, to create a skeleton where the last bone joins back to the first, i.e. a loop. Of course this example only has one degree of freedom, zRotation, and 2 or 3 degrees of freedom would make it far more complex. But in principle it's possible.

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The 3Dcheapskate* occasionally posts sensible stuff. Usually by accident. And it usually uses Poser 11, with units set to inches. Except when it's using Poser 6 or PP2014, or when its units are set to PNU or something else.
*soon only to be available in two flavours -  DAZ and Renderosity