|The Last Supper
The "Last Supper" of Christ is the Passover meal he took with his apostles on the night before he died. Occasionally a detail in a Last Supper image will serve to remind the viewer of this connection with Passover (example).
The synoptic gospels trace the institution of the Eucharist to the Last Supper. For this reason, we often see eucharistic imagery in pictures of this event. The catacomb painting at left, for example, has baskets and fish representing the multiplication of the loaves and fishes, a miracle that Christ explicitly associated with the Eucharist in the "Bread of Life" discourse (cached) in John's Gospel.
We see an even bolder stroke of Eucharistic imagery when Christ is represented as giving his apostles communion hosts, which they receive on the tongue in the manner of communicants in the medieval mass (examples from the 13th, 15th, 16th, and 17th centuries). Tintoretto's most famous Last Supper manages to combine what look like liturgical vessels, gestures, and lighting effects into an otherwise bustling 16th-century banquet scene.
In medieval examples the apostles are usually arranged around the table, even if this means having some of their backs to the viewer (example). But there is one type of Last Supper in which they all sit on the far side of the table while a small figure on the near side reaches up to hand something to Christ (examples: a 13th century Jesse Tree window and a copper and gold relief in the Cluny Museum). Da Vinci's famous 1498 treatment also arranges the apostles on the far side of the table, though without the small figure.
The Pretty Man
In the da Vinci painting the person on Christ's right hand is most certainly the apostle John. He looks rather girlish to modern eyes, and a recent scandalous book claims that he is really Mary Magdalene. But an understanding of the iconography of St. John provides two excellent reasons for rejecting such a claim.
First, a medieval and Renaissance way of representing a man as young is to show him as beardless and girlish (examples by Castagno and Giotto, also see portraits of St. Sebastian).Clearly then, the pretty young person at Christ's side in the da Vinci painting is not a coded revelation about the Magdalene but simply a recursion to the conventional iconography of St. John.
The Washing of the Feet
Secondary topics treated in other Last Supper images include Christ's washing of the apostles' feet in John 13:4-17. John records that Peter at first demurred from having the Lord wash his feet, but when Jesus insisted Peter asked that he also wash his head and hands. In some 13th-century images Peter puts his hand to his head in reference to the follow-up request (example). Some of Tintoretto's numerous images of the foot-washing present the initial refusal instead (example); one of them collapses the two moments into a single animated colloquy between Peter and Christ.
Feast day: the Thursday before Good Friday
At left, 3rd-century catacombs painting
6th-century mosaic in RavennaScripture: