The lines of perspective meet in Christ's right eye, thus making him the central figure of the painting. The rest of the scene is organized in order to emphasize this centrality. Leonardo grouped the apostles into four groups of three, with Jesus in the middle. From left to right are, they are:
Group One: Bartholomew, James the Lesser and Andrew form the first group of three, all of them appearing surprised. Andrew holds both of his hand up in front of him in a frightened gesture.
Group Two: Judas Iscariot, Simon Peter and John form the second group of three. Judas is holding a bag of silver in his right hand, while reaching for a piece of bread with his left. Simon Peter is leaning over the shoulder of John, a knife held in his right hand, symbolizing his zealous defence of Jesus. John appears to be swooning.
Group Three: The third group is made of Thomas, James the Great and Phillip. These three appear in varying degrees of shock; Thomas, with his hand raised, and Phillip seem to be requesting some sort of explanation, while James the Great, between them, appears to be recoiling from Jesus in horror.
Group Four: The last three, Matthew, Jude Thaddeus and Simon the Zealot appear to be discussing the matter with each other, in a rendition of Luke 22:23: "They began to question among themselves which of them it might be who would do this."
http://www.abcgallery.com/L/leonardo/leonardo4.html
