Inferior view of left temporal bone. The temporal bone consists of four parts: squamous, petrous, tympanic, and mastoid. The squamous part is located anterolaterally and includes the zygomatic process that unites with the temporal process of the zygomatic bone to form the zygomatic arch, the mandibular or glenoid fossa for the condyle of the mandible, and the thin scale-like squamous part that presents both intra- and extracranially. The petrous part is highly mineralized and dense and houses the middle and inner ear structures. Its inferior surface 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. The styloid process is derived from cartilage (Reichert's cartilage) of the second pharyngeal arch. Numerous ligaments and muscles attach to it. The jugular fossa contains the jugular bulb and forms the anterior margin of the jugular foramen. The mastoid part is posteroinferior to the squamous part and features the mastoid process containing air cells, the mastoid notch or digastric groove for attachment of the posterior digastric muscle, and the groove for the occipital artery. The tympanic part of the temporal bone lies inferior to the squamous part, anterior to the mastoid portion, and forms the bony walls of the external auditory canal. A portion of it (vaginal process) splits to enclose the root of the styloid process. The tympanomastoid suture separates the mastoid and tympanic parts and leads to the stylomastoid foramen located between the styloid and mastoid processes. The facial nerve exits this foramen. The petrotympanic fissure divides the mandibular fossa anteromedially from the tympanic part posteriorly and contains the chorda tympani and anterior tympanic artery. (Image courtesy of AL Rhoton, Jr.)