  We have investigated a closed system of equations for the quark propagator,
obtained earlier within our general approach to QCD at low energies. It implies
quark confinement (the quark propagator has no pole, indeed), as well as the
dynamical breakdown of chiral symmetry (a chiral symmetry preserving solution
is forbidded). This system can be solved exactly in the chiral limit. We have
established the space of the smooth test functions (consisting of the Green's
functions for the quark propagator and the corresponding quark-gluon vertex) in
which our generalized function (the confining gluon propagator) becomes a
continuous linear functional. It is a linear topological space $K(c)$ of the
infinitely differentiable functions (with respect to the dimensionless momentum
variable $x$), having compact support in the region $x \leq c$. We develop an
analytical formalism, the so-called chiral perturbtion theory at the
fundamental quark level, which allows one to find explicit solution for the
quark propagator in powers of the light quark masses. We also develop an
analytical formalism, which allows one to find the solution for the quark
propagator in the inverse powers of the heavy quark masses. It justifies the
use for the heavy quark propagator its free counterpart up to terms of the
order $1/m_Q^3$, where $m_Q$ is the heavy quark mass. So this solution
automatically possesses the heavy quark spin-flavor symmetry.
