Just above the skeleton it reads "IO FU[I] G[I]A QUEL CHE VOI S[I]ETE E QUEL CH['] I[O] SONO VO[I] A[N]C[OR] SARETE" (I once was what you are and what I am you also will be). This memento mori underlines that the painting was intended to serve as a lesson to the viewers.
Sue Duran