  We discuss the evolution of the ratio in number of recombinations due to 2s
two photon escape and due to the escape of Lyman-$\alpha$ photons from the
resonance during the epoch of cosmological recombination, within the width of
the last scattering surface and near its boundaries. We discuss how this ratio
evolves in time, and how it defines the profile of the Lyman-$\alpha$ line in
the spectrum of CMB. One of the key reasons for explaining its time dependence
is the strong overpopulation of the 2p level relative to the 2s level at
redshifts $z \la 750$.
