  Published parametric models of the Einstein Cross gravitational lens
demonstrate that the image geometry can be reproduced by families of models. In
particular, the slope of the mass-profile for the lens galaxy is unconstrained.
However, recent models predict a dependence of image flux ratios on the slope
of the mass profile. We use this dependence to constrain the mass profile by
calculating the likelihood of the slope using published mid-IR flux ratios
(including microlensing variability). We find that the galaxy is likely to be
flatter than isothermal, and therefore that the mass-to-light ratio is
decreasing in the inner kpc.
