Venous sinuses exposed following mastoidectomy. In this perspective, the right mastoid process has been drilled out to expose dura containing the sigmoid sinus, which continues as the jugular bulb. The superior petrosal sinus can be observed. It drains the cavernous sinus and courses within the tentorial attachment to the superior border of the petrous bone and empties into the transverse sinus near its junction with the sigmoid sinus. The middle ear cavity has been opened and the mastoid segment of the facial nerve can be seen descending toward the stylomastoid foramen. (Image courtesy of AL Rhoton, Jr.)