  The solar and baseline neutrino oscillation data suggest bimaximal neutrino
mixing among the first two generations, and trimaximal mixing between all three
neutrino flavors. It has been conjectured that this indicates the existence of
an underlying symmetry for the leptonic fermion mass textures. The
experimentally measured quantities however, are associated to the latter
indirectly and in a rather complicated way through the mixing matrices of the
charged leptons and neutrinos. Motivated by these facts, we derive exact
analytical expressions which directly link the charged lepton and neutrino mass
and mixing parameters to measured quantities and obtain constraints on the
parameter space. We discuss deviations from Tri-Bi mixing matrices and present
minimal extensions of the Harrison Perkins and Scott matrices capable of
interpreting all neutrino data.
