Landmarks of a left presigmoid exposure. The auricle of the ear (toward left border of image) has been retracted anteriorly. Superficial landmarks visible here include the mastoid tip (drilled) with the mastoid notch and insertion of the posterior digastric muscle just deep to the tip. The root of the zygomatic process serves as a superficial landmark for the floor of the middle cranial fossa. Just deep to the zygomatic root is the Vein of Labbe, which courses from the Sylvian fissure posteriorly to enter the sinus at the transverse-sigmoid junction. The Spine of Henle is a small bony spinous process which sits superior and posterior to the external acoustic meatus and is a projection for attachment of the auricular cartilage. Deep to the Spine of Henle within the temporal bone are the semicircular canals and the facial nerve; the mastoid segment of the facial nerve is visible here coursing inferiorly toward the stylomastoid foramen. (Image courtesy of AL Rhoton, Jr.)