  The effective quark interactions that break explicitly the chiral SU(3)_L X
SU(3)_R and U_A(1) symmetries by current-quark mass source terms are considered
in NLO in $N_c$ counting. They are of the same order as the 't Hooft flavor
determinant and the eight quark interactions that extend the LO
Nambu-Jona-Lasinio Lagrangian, and complete the set of non-derivative and spin
0 interactions relevant for the $N_c$ scheme. The bosonized Lagrangian at meson
tree level describes accurately the empirical ordering and magnitude of the
splitting of states in the low lying pseudoscalar and scalar meson nonets, for
which the explicit symmetry breaking terms turn out to be essential. The strong
interaction and radiative decays of the scalar mesons are understood in terms
of the underlying microscopic multi-quark states, which are probed differently
by the strong and the electromagnetic interactions. We also obtain that the
anomalous two photon decays of the pseudoscalars are in very good agreement
with data.
