What is painted on the ceiling of the dungeon?

When the narrator first wakes up in the dungeon, it is completely dark, and he can't see any part of his cell. This state continues for some time, and he manages to explore his room and avoid falling into the pit. After he is drugged and wakes up again, he finds himself strapped to a wooden platform. First he looks at the walls of the room and sees that they are painted with dull figures...

When the narrator first wakes up in the dungeon, it is completely dark, and he can't see any part of his cell. This state continues for some time, and he manages to explore his room and avoid falling into the pit. After he is drugged and wakes up again, he finds himself strapped to a wooden platform. First he looks at the walls of the room and sees that they are painted with dull figures of menacing monsters and skeletons. Then, looking up, he notices 30 to 40 feet above him the ceiling, and on one of the panels is a painted image of Time personified. This figure, known either as Father Time or the Grim Reaper, is usually pictured in a black robe, not unlike the black-robed judges of the first paragraph, with a scythe (see image at link below). However, the depiction of Father Time the man sees on the ceiling does not include a scythe, but rather a pendulum, like that of a grandfather clock. When the man looks more carefully, however, he can see that the pendulum is not painted on the ceiling, but is actually a three-dimensional object, and it is ever-so-gradually descending toward him.