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