19th Century engraved bone triptych of the Madonna

The triptych is engraved on bone, which is mounted onto a hinged wooden frame. Of arch form, the triptych opens outward to display three pictorial panels - one large central panel and two narrower flanking panels, all of which are bordered by an engraved scrolling foliate pattern. The central panel is the largest and depicts the Madonna wearing a crown with a halo, seated holding a book backed with swathed material. The left flanking panel depicts a young woman standing holding a casket, and the right flanking panel depicts a young man standing holding a vase. The central panel is monogrammed to the left of the Madonna with the initials 'JP.'