Inferior View of the Middle and Posterior Cranial Base. The squamosal part of the temporal bone forms the posterior part of the floor and lateral wall of the middle cranial fossa, the roof of the mandibular fossa in which the mandibular condyle sits, and the posterior part of the zygomatic arch. The tympanic part of the temporal bone forms the anterior, lower, and part of the posterior wall of the external canal, part of the osseous floor of the tympanic cavity and Eustachian tube, and the posterior wall of the mandibular fossa. The mastoid part contains the mastoid air cells and mastoid antrum. The petrous part is the site of the auditory and vestibular labyrinth, the carotid and facial canals, and the internal acoustic meatus. The external orifice of the carotid canal opens anterior to the jugular foramen. The jugular fossa, in which the jugular bulb sits, is located on the lower surface of the petrous part. The stylomastoid foramen opens between the anterior edge of the digastric groove and the styloid process. The styloid part projects downward behind the tympanic part and serves as the site of attachment of the three styloid muscles. (Image courtesy of AL Rhoton, Jr.)