His bones are as strong pieces of brass; rather, as tubes of bronze. The great thigh-bones— μηρία of the Greeks—are probably intended. These are hollow, being filled with marrow, and are so strong that they may be well compared to "tubes of bronze."
His bones (rather, his ribs) are like bars of iron. Either the ribs, or the solid bones of the lower leg, forearm, etc; are intended.