We present a multiple scale method for modeling multiple crack growth in cortical bone under tension. The four phase composite Haversian microstructure is discretized by a Finite Element Method. The geometrical and mechanical bone parameters obtained by experiments mimic the heterogeneity of bone at the micro scale. The cracks are initiated at the micro scale where a critical elastic-damage strain driven criterion is met and are grown until complete failure in heterogeneous linear elastic media when a critical stress intensity factor criterion is reached. The cracks are modeled by the eXtended Finite Element Method. The simulations provide the global response at the macroscopic level and stress and strain fields at the microscopic level. The model emphasizes the importance of the microstructure on bone failure in assessing the fracture risk.