A corner joint particularly for modular cages, which is monolithic and has a substantially L-shaped body that comprises abutments inside the corner region, the transverse cross-sections of its arms being substantially H-shaped. Two channels with curled-in edges for each one of the arms are thus formed. The channels are open outward, on each arm, in opposite directions, and are capable of accommodating with reversible interlocking a total of four converging walls. The corner joint is symmetrical with respect to a central plane that is perpendicular to the converging walls.