Joos van Wassenhove, The Last Supper
Medium: The museum label simply says it is "tavola."
Ducal Palace, Urbino
The painting presents the Last Supper as a Catholic Mass. From behind the table, St. John acts as an altar server, placing a cruet of either wine or water beside the chalice. Both vessels are of the type used in the Mass even today.
In front of the table, Jesus' left hand holds a paten (also identical to those used in the divine service) while with his right he distributes round, white hosts to the apostles, who are kneeling as all communicants were required to do when receiving the host. (This requirement ended only in the 20th century.)
Federico da Montefeltro stands on the right behind the kneeling apostles. The boy behind him could be his son Guidobaldo.
This image in full resolution
More of the Last Supper
More of the apostles as a group
Photographed at the site by Richard Stracke, shared under Attribution-NonCommercial-ShareAlike license.