  A generalized 3 flavor Nambu-Jona--Lasinio Lagrangian including the explicit
chiral symmetry breaking interactions which contribute at the same order in the
large $1/N_c$ counting as the $U_A(1)$ 't Hooft flavor determinant is
considered to obtain the mixing angles in the $\pi^0-\eta-\eta'$ system and
related current quark mass ratios in close agreement with phenomenological
values. At the same time an accurate ordering and magnitude of the splitting of
states in the low lying pseudoscalar nonet is obtained.
