Internal surface

The internal surface of the frontal bone faces the brain. It consists of a cranial (caudal) portion and a facial (rostral) portion, separated from each other by a strong transverse crest that joins the ethmoid bone. It thus delineates the cranium and the face.

Its cranial portion, belonging to the cranial cavity, is concave and presents irregular ridges corresponding to the impressions of the cerebral convolutions. The ethmoidal foramen opens in this region, near the ethmoid bone.

Its facial portion contributes to the delimitation of the frontal sinus (sinus frontalis). This sinus can be subdivided into irregular compartments by incomplete bony septa, or even by complete septa dividing several frontal sinuses, particularly in ruminants, pigs, and carnivores. The frontal sinus extends between the external and internal tables of the bone, potentially reaching the cranial part over a variable extent depending on the species and, in cattle and pigs, sometimes even extending to neighboring bones.