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Heart is mainly protected by the rib cage.

Spinal Cord
Spinal Cord is protected by 33 pairs of vertebrae which collectively form the bony structure called Vertebral Column which contains Cerebrospinal Fluid.

Brain is protected by a bony box of skull called Cranium and three pairs of membranes surrounding it called Meninges. There is also Cerebrospinal Fluid which absorbs shocks.