  An exact form is presented for the axial-vector Bethe-Salpeter equation,
which is valid when the quark-gluon vertex is fully dressed. A Ward-Takahashi
identity for the Bethe-Salpeter kernel is derived therefrom and solved for a
class of dressed quark-gluon vertex models. The solution provides a
symmetry-preserving closed system of gap and vertex equations. The analysis can
be extended to the vector equation. This enables a comparison between the
responses of pseudoscalar- and scalar meson masses to nonperturbatively
dressing the quark-gluon vertex. The result indicates that dynamical chiral
symmetry breaking enhances spin-orbit splitting in the meson spectrum.
