Complex sentence: The small Philadelphia panel is painted with oil on vellum mounted on parchment similar to those seen in contemporary illuminated manuscripts, and gives the illusion of the viewer looking through a window into the landscape.
Split into simpler sentences: The small Philadelphia panel is painted with oil on vellum. The Philadelphia panel is painted with oil on vellum mounted on parchment similar to those seen in contemporary illuminated manuscripts, and gives the illusion of the viewer looking through a window into the landscape.