Cradles without front structural supports (4)

I believe the answer is:

ribs

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'supports' is the definition.
(rib is a kind of support)

I don't understand how the rest of the clue works.

(Other definitions for ribs that I've seen before include "cage" , "Pairs of curved bones" , "Bones in chest, may be floating" , "Spurs?" , "Arched bones in the upper body" .)

I've seen this clue in The Independent.

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