  A mathematical model of the distribution function for the discrete 3-disk is
proposed in order to utilize in the statistical evolution equation of the
3-dimensional Universe. The model distribution is constructed based on analyses
in known exact solutions of recursion equations for the generating functions of
the discrete 2-disk.The proposed distribution function is compared with
numerical simulations of the dynamical triangulation with $ S^3 $, and $ D^3 $
topologies.The model distribution exhibits three types of phases characterized
by geometrical nature of the disk with either 1, 2, or 3- dimensional
structure.Transitions between those phases are either cross-over, 1st order, or
2nd order depending on the parameters, which reflect the type of discretization
and matter fields coupled to space.
