Bones placed in a circle (5)

I believe the answer is:

radii

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'bones' is the definition.
(radius is a kind of bone)

I can't explain the rest of the clue.

(Other definitions for radii that I've seen before include "Halves of diameters" , "Halves of diameter" , "Half-diameters" , "They meet in the middle of a circle" , "Lines from the centre to the circumference of a circle" .)

I've seen this clue in The Globe and Mail.

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