E, Lateral view of the temporal bone. The squamosal part forms part of the lateral wall of the middle fossa, the posterior part of the zygomatic arch, and the upper part of the mandibular fossa. The tympanic part forms the posterior wall of the mandibular fossa and almost all of the wall of the external canal. The styloid process is ensheathed at its base by the tympanic part and projects downward, serving as the attachment of several muscles. The mastoid part is located posteriorly and contains the mastoid air cells that coalesce at the mastoid antrum. F, Enlarged view of the external auditory canal. The spine of Henley, an excellent landmark for locating the deep site of the lateral canal and tympanic segment of the facial nerve, is located along the posterosuperior margin of the external canal. The mastoid antrum is located deep to the depressed area, called the suprameatal triangle, located behind the spine of Henley. The view into the canal exposes the tympanic cavity, which has the promontory overlying the basal turn of the cochlea and the oval and round windows in its medial wall. G, Lateral surface of the temporal bone in the intact skull. The tympanic part forms the anterior and lower and part of the posterior wall of the external canal. The mandibular fossa is formed above and anteriorly by the squamosal part and behind by the tympanic part. The mastoid antrum is located posterosuperior to the spine of Henley, between the spine of Henley and the anterior part of the supramastoid crest. The asterion, the junction of the lambdoid, parietomastoid, and occipital mastoid sutures, is usually located over the lower half of the junction of the sigmoid and transverse sinuses. The midpoint of the parietal mastoid suture is usually located at the anterior margin of the junction of the transverse and sigmoid sinuses, and the lateral edge of the petrous ridge is located at the junction of the squamosal suture and the supramastoid crest. H, The supra- and infratentorial areas have been exposed while preserving the bone at the site of the sutures. The asterion, located at the junction of the lambdoid, occipitomastoid, and parietomastoid sutures, overlies the lower half of the junction of the transverse and sigmoid sinuses. The junction of the supramastoid crest and the squamosal suture is located at the posterior edge of the middle fossa and slightly anterior and above the junction of the transverse and sigmoid sinuses. (Images courtesy of AL Rhoton, Jr.)