  The leading order evolution of parton orbital angular momenta is treated in
the probabilistic manner. As a result, the splitting probability matrix, while
coinciding with the recent explicit calculations, is expressed in the terms of
the standard spin-dependent and spin-averaged kernels. The implied relations
between spin and orbital angular momenta evolution kernels may be interpreted
as resulting from the ambiguity in the separation of the angular momenta to the
spin and orbital contributions and are likely to be valid for higher orders and
twists. Consequently, the orbital and total angular momenta may be considered
as decoupling from the spin ones, the latter being the only elements of nucleon
structure accessible via the hard scattering of polarized particles. In
particular, the partition of the total angular momenta of quarks and gluons
should be analogous to that of their momentum at any $Q^2$, generalizing the
earlier finding for asymptotic limit by Ji, Tang and Hoodbhoy.
