Corrections of order (Z\alpha)^6 m_e^2/m_\mu in the muonium fine   structure
  In the framework of the quasipotential method we calculate the contributions of the kind (Z\alpha)^6m_e^2/m_\mu to the energy spectrum of the muonium n^3S_1 states. Numerical value of obtained correction for 2^3S_1-1^3S_1 muonium fine structure interval is equal to 0.19 MHz. 
R.N.Faustov and A.P.Martynenko