Weingarten Abbey Scriptorium
The Berthold Sacramentary: Pentecost
Pierpont Morgan Library, accession M710, folio 64 verso
The image pictures the Pentecost event recounted in Acts 2. The dove descends from the top of the arch, bearing a cruciform halo like that seen in images of Christ. The main figures are Saints Peter with his keys and Paul with his book. Paul became an Apostle only later in the Acts narrative, but it was not uncommon to picture him in the Pentecost group.
Of the other ten Apostles eight share the circular bench with Paul and Peter, while two sit apparently on the floor. The bearded man sitting at Paul's left is probably St. Andrew, identified by the cowlick on his forehead; it was traditional to picture him with wild hair. The beardless man sitting across from him on Peter's right would then possibly be Andrew's brother John.
In Acts 2:2 a sound comes upon the Apostles "as of a mighty wind." This is represented by the vase-bearers in the four corners. It was traditional to picture the four winds in this way, as for example in this diagram:
Read more about images of Pentecost.
Source: Wikimedia Commons