Inferior surface of petrous part

The inferior surface of petrous part of temporal bone presents as a rugged, irregular, wedge-shaped structure replete with noteworthy anatomical landmarks.

Near the apex, a coarse quadrilateral zone takes residence, serving both as the site of attachment for the levator veli palatini muscle and the cartilaginous part of the auditory tube. The apex itself unites with the basilar section of the occipital bone via a dense fibrous tissue that occludes the foramen lacerum. Positioned posterolateral to the quadrilateral zone, lies the circular entrance of the carotid canal. This canal makes a forward and medial progression through the bone, facilitating the passage of internal carotid artery and the sympathetic nerve fibers of the carotid plexus.

Just behind the opening of the internal carotid artery, you'll find an opening called the jugular foramen. This opening is split by a piece of bone called the intrajugular process into two sections: a bigger outer one called the jugular fossa, and a smaller medial one named the petrosal compartment. A triangular depression is situated anteromedial to the jugular fossa, mostly in the petrosal compartment but also stretching back into the posterior cranial fossa. It’s in this area that the cochlear canaliculus can be found opening up.

Tucked into the bony ridge that lies between the carotid canal and jugular fossa is the inferior tympanic canaliculus. This subtle canal provides a route for the tympanic nerve, branching from the glossopharyngeal nerve. The jugular fossa's lateral wall houses the mastoid canaliculus, an entryway for the auricular branch of the vagus nerve.

Moving laterally from the end of the carotid canal, the vaginal process unfolds backward and outward. This process resembles a sheath-like bony plate, splitting into two layers or laminae. The lateral layer joins the tympanic bone, while the medial layer becomes the side wall of the jugular fossa. Nestled between these two plates is the slender styloid process. The stylomastoid foramen, squeezed between the styloid and mastoid processes, marks the end of the facial canal. It allows both the facial nerve and the stylomastoid artery to emerge. Lastly, the tympanomastoid fissure, the space between the tympanic part and the mastoid part, serves as the exit for the auricular branch of the vagus nerve, after it has navigated through the temporal bone from the mastoid canaliculus to this fissure.