Cut and reflect the dura mater from the skull and brain.

1. Use scissors to cut the dura from anterior to posterior along the original cut line in the skull. Do not extend the cut across the midline (through the superior sagittal sinus and falx cerebri).
2. Lift the dura from the front part of the brain, place the scissors between the cerebral hemispheres, and cut the falx cerebri (midline dural reflection) from its attachment to the crista galli. (G 7.24A;N 102;GI 34.13) Pull the falx cerebri from between the cerebral hemispheres.   You will need to tear the superficial cerebral veins where they drain into the superior sagittal sinus (where the falx cerebri meets the dura overlying the lateral aspect of the cerebral hemisphere).  
3. On both sides, lift the posterior-lateral aspect of the cerebral hemispheres and use a scalpel to cut the tentorium cerebelli from the petrous portion of the temporal bone. (G 7.26;N 103;GI 34.15) Pull the tentorium cerebelli from between the cerebral hemispheres and the underlying cerebellum. Finish reflecting the dura mater and cut it free from the skull down to the foramen magnum. Set it aside for later steps.