  Using magnetocapacitance data in tilted magnetic fields, we directly
determine the chemical potential jump in a strongly correlated two-dimensional
electron system in silicon when the filling factor traverses the spin and the
cyclotron gaps. The data yield an effective g-factor that is close to its value
in bulk silicon and does not depend on filling factor. The cyclotron splitting
corresponds to the effective mass that is strongly enhanced at low electron
densities.
