Step 4. Identify the antrum (continued)

4.3 Rotate the specimen so that the long sweeps may be continued parallel with the middle fossa. Remove the cellular bone from the ear canal to the sinodural angle. This requires removal of superficial air cells attached to the canal so there is room to move in the depth of the cavity.

The cortical bone of the canal wall should be ignored unless the pneumatisation of the bone is restricted. The middle fossa is followed to the depth of the mastoid antrum.