Based on the experimental results obtained by splitting a rabbit femur, the mandible in a human cadaver was split by the sagittal splitting technique. In addition to macroscopically and microscopically examining the course of the fracture line, three-dimensionally reconstructed images were studied. Macroscopic examination showed that the course of a fracture line was nearly constant. On microscopic examination, we confirmed a trend for the course of the fracture line to be along the cementing

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... ne or the curve of the haversian lamella, or both. The three-dimensionally reconstructed images showed that the fracture surface was nearly parallel to the direction of the haversian canal. These findings indicate that the course of fracture line is influenced by the structures composing lamellar bone, such as the haversian canal, haversian lamella, interstitial lamella, and cementing line. These structures may account for the preferred path of fracture lines in the bone. Furthermore, we confirmed that the direction of the chisels used for sagittal splitting was appropriate.