Petrooccipital fissure

Rostrally to the jugular foramen, the basis of the tympanic bulla merges in most species to the basilar part of the occipital bone, in order to separate the jugular foramen from the foramen lacerum.

In Horses, Bulls, and Pigs, this adjoining is missing and a petro-occipital fissure (Fissura petrooccipitalis) make these orifices come together in a single and vast occipitosphenotemporal hiatus.

In Dogs, a petro-occipital canal (Canalis petrooccipitalis) runs back to front from the jugular foramen through the petro-occipital synchondrosis.