  Effect of the quark intrinsic motion on the proton spin structure functions
is demonstrated. It is shown, that the covariant version of the quark-parton
model taking into account the orbital motion gives the consistent picture of
the proton spin structure, which is based on the valence quarks. This picture
is supported by the recent data, which indicate, that the spin contributions
from the sea quarks and gluons are compatible with zero.
