  Independent of assumptions about the form of the quark-quark scattering
kernel, K, we derive the explicit relation between the flavour-nonsinglet
pseudoscalar meson Bethe-Salpeter amplitude, Gamma_H, and the dressed-quark
propagator in the chiral limit. In addition to a term proportional to gamma_5,
Gamma_H necessarily contains qualitatively and quantitatively important terms
proportional to gamma_5 gamma.P and gamma_5 gamma.k k.P, where P is the total
momentum of the bound state. The axial-vector vertex contains a bound state
pole described by Gamma_H, whose residue is the leptonic decay constant for the
bound state. The pseudoscalar vertex also contains such a bound state pole and,
in the chiral limit, the residue of this pole is related to the vacuum quark
condensate. The axial-vector Ward-Takahashi identity relates these pole
residues; with the Gell-Mann--Oakes-Renner relation a corollary of this
identity. The dominant ultraviolet asymptotic behaviour of the scalar functions
in the meson Bethe-Salpeter amplitude is fully determined by the behaviour of
the chiral limit quark mass function, and is characteristic of the QCD
renormalisation group. The rainbow-ladder Ansatz for K, with a simple model for
the dressed-quark-quark interaction, is used to illustrate and elucidate these
general results. The model preserves the one-loop renormalisation group
structure of QCD. The numerical studies also provide a means of exploring
procedures for solving the Bethe-Salpeter equation without a three-dimensional
reduction.
