Frontal bone

Overview
The frontal bone is a bone in the human skull that resembles a cockleshell in form, and consists of two portions:


 * a vertical portion, the squama frontalis, corresponding with the region of the forehead.
 * an orbital or horizontal portion, the pars orbitalis, which enters into the formation of the roofs of the orbital and nasal cavities.

Borders
The border of the squama temporalis is thick, strongly serrated, bevelled at the expense of the inner table above, where it rests upon the parietal bones, and at the expense of the outer table on either side, where it receives the lateral pressure of those bones; this border is continued below into a triangular, rough surface, which articulates with the great wing of the sphenoid. The posterior borders of the orbital plates are thin and serrated, and articulate with the small wings of the sphenoid.

Structure
The squama and the zygomatic processes are very thick, consisting of diploic tissue contained between two compact laminæ; the diploic tissue is absent in the regions occupied by the frontal air sinuses.

The orbital portion is thin, translucent, and composed entirely of compact bone; hence the facility with which instruments can penetrate the cranium through this part of the orbit; when the frontal sinuses are exceptionally large they may extend backward for a considerable distance into the orbital portion, which in such cases also consists of only two tables.