The base of the temporal bone is made of the petrous part, the tympanic part and the endotympanic part -when there is one-; it is directed in ventral direction and entirely visible at the ventral side of the skull.
Totally medially, a very irregular border separates the basis of the auricular part of the temporal bone from its cerebellar surface. At the caudal extremity, this border is indented by the jugular notch(Incisura jugularis), belonging to the petrous part and participating in forming with the similar indentation of the occipital bone, the jugular foramen.
Rostrally to this hole, 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) gathers the above-mentioned orifices in a single and vast hiatus occipitosphenotemporal. In Dogs, the petro-occipital canal (Canalis petrooccipitalis) runs back to front from the jugular foramen through the petro-occipital synchondrose. Finally in most species (Men, Carnivorous, Rabbit) the internal carotid artery passes through a bony canal before entering the cranium.
This carotid canal starts from the rostral border of the jugular foramen and bends in rostral direction against the medial wall of the eardrum to end on the caudal border of the foramen lacerum. It is vestigial in Pigs, where a secondary carotid branch enters in the cranium, as the internal carotid in Equidae. In Equidae, the internal carotid artery passes directly through the carotid foramen, only represented on the dry skeleton by the carotid notch (Incisura carotica) on the rostral border of the foramen lacerum. As the internal carotid artery, the carotid canal and carotid foramen are missing in Ruminants.