Inferior view of right temporal bone. The tympanic portion of the temporal bone forms the posterior wall of the mandibular fossa, which borders on the front of the bony external auditory canal. The mastoid portion is located immediately posterior to the tympanic part and features the mastoid process containing air cells and antrum, the digastric groove or mastoid notch for attachment of the posterior digastric muscle, and the groove for the occipital artery. The inferior surface of the petrous part includes the styloid process, stylomastoid foramen, jugular fossa, and carotid canal (both external and internal openings). Medial to the jugular fossa is a triangular depression that contains the opening of the cochlear aqueduct for communication of the perilymphatic space of the inner ear with the subarachnoid space. In the lateral part of the jugular fossa is the mastoid canaliculus (Arnold's canaliculus) for entrance of the auricular branch of the vagus nerve (Arnold's nerve). Between the jugular foramen and external opening of the carotid canal is a bony ridge that contains a small passageway, the inferior tympanic canaliculus, for the tympanic branch (Jacobsen's nerve) of the glossopharyngeal nerve. (Image courtesy of AL Rhoton, Jr.)