  In this paper we present a theoretical model for the dewetting of ultra-thin
polymer films. Assumming that the shear-thinning properties of these films can
be described by a Cross-type constitutive equation, we analyze the front
morphology of the dewetting film, and characterize the time evolution of the
dry region radius, and of the rim height. Different regimes of growth are
expected, depending on the initial film thickness, and on the power-law index
involved in the constitutive equation. In the thin-films regime, the dry radius
and the rim height obey power-law time dependences. We then compare our
predictions with the experimental results obtained by Debr\'egeas {\it et al.}
[Phys. Rev. Lett. {\bf 75}, 3886 (1995)] and by Reiter [Phys. Rev. Lett. {\bf
87}, 186101 (2001)].
