Reliquaire (reliquary)

An often richly decorated container holding the remains of a saint.
The whole or almost the whole corpse of a saint is normally stored in a châsse (chasse).
Small singular parts (heart, nails) are normally kept in a smaller container, the reliquaire.
The box in the picture contains the remains of Saint-Philibert (Saint-Philibert in Tournus).

Saint-Philibert - Tournus