Internal surface
Facies interna
Definition
The internal surface (Facies interna) of the frontal bone is divided in two parts by a strong transversal crest that unites the frontal to the ethmoid bone; it is a true ethmoidal border (Margo ethmoidalis) that constitutes the limit between the cranium and the face.
a) The caudal or cranial part, concave in all directions, belongs to the cranial cavity. It is crossed by irregular reliefs (Juga cerebralia), delimitating the impressions of the cerebral gyri (impressiones digitatae). The ethmoidal foramen opens on the edge that connects the frontal to the ethmoidal bone.
b) The rostral or facial part, carved by many chambers, contributes to delimitate the frontal sinus (Sinus frontalis) that can be divided into irregular lodges by complete (Ruminants; Pigs, Carnivorous) or incomplete bony walls; it extends between the internal and external tables of the bone, until the cranial part, more or less far according to the species and sometimes even (Bulls, Pigs) until the neighboring bones.
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