A, Superior view of the temporal bone and infratemporal fossa and orbit. The floor of the middle fossa has been removed to expose the temporalis muscle in the temporal fossa and the pterygoid muscles and branches of the third trigeminal division in the infratemporal fossa. The posterior part of the middle fossa forming the upper surface of the temporomandibular joint has been removed to expose the mandibular condyle. The internal acoustic meatus extends laterally from the posterior surface of the temporal bone. The mastoid is located behind the external canal and lateral to the semicircular canals and vestibule. B, Enlarged view. The trigeminal nerve has been reflected forward and bone has been removed over the eustachian tube, tensor tympani muscle, petrous carotid, and internal acoustic meatus. Dura has been removed from the lateral wall of the cavernous sinus to expose the trochlear, trigeminal, and oculomotor nerves in the sinus wall and the abducens nerve passing below the petrosphenoid ligament and through Dorello’s canal. The greater petrosal nerve is joined by the deep petrosal branches of the carotid sympathetic plexus to form the vidian nerve, which passes forward in the vidian canal, which has been unroofed. The lesser petrosal nerve arises from the tympanic branch of the glossopharyngeal nerve, which passes across the promontory in the tympanic nerve plexus and regroups to cross the floor of the middle fossa, exiting the skull to provide parasympathetic innervation through the otic ganglion to the parotid gland. The tensor tympani muscle and eustachian are layered along, but are separated from, the anterior surface of the petrous carotid by a thin layer of bone. (Images courtesy of AL Rhoton, Jr.)