External surface

The external or exocranial surface of the parietal bone is usually convex. It is crossed by a curvy line in rostrolateral direction: the temporal line (Linea temporalis) which goes on on the interparietal and frontal bones to delimitate the temporal fossa. This line (double in Men) divides the external surface of the parietal bone into two areas. On the ventrolateral side, the temporal surface or planum temporal is a part of the temporal fossa and gives attachment to the temporal muscle. On the dorsomedial side, the parietal surface or planum parietale connects on the median plane with the one of the opposite side. The aspect and the extend of this surface varies much according to the species:

In Carnivorous, Equidae, Camelidae, it is triangular with a caudal summit. The two temporal lines unite caudally in an external sagittal crest (Crista sagittalis externa) that goes on between the two temporal fossae on the interparietal bone and the external occipital protuberance.

In Pigs, small Ruminants, Rabbits and Men, the temporal lines stay separated and the temporal fossae are pushed on the sides of the head; there is no external sagittal crest in these species. The vault is particularly vast in Men.

In Bulls, the extreme development of the frontal bones pushes the parietal bone on the nuchal surface of the skull; the planum parietale becomes then a planum nuchale, very stretched from side to side. The temporal lines are particularly spaced.