This section is from the book "Applied Anatomy: The Construction Of The Human Body", by Gwilym G. Davis. Also available from Amazon: Applied anatomy: The construction of the human body.
The frontal bone develops from two centres of ossification, one on each side. These unite in the median line to form the frontal suture which joins the anterior fontanelle and is closed about the same time, within the age of two years. The suture occasionally persists through life and sometimes the line of junction can be felt in the living; it should not be mistaken for fracture.
The frontal eminences in the child are particularly prominent, the forehead projecting beyond the edge of the orbit. This makes it difficult to apply a bandage securely to the head in children unless it is twisted to draw in its sides.
The superciliary ridges are about a centimetre above the edge of the orbit over its inner half. Aided by the hair of the eyebrows they serve to divert the sweat to the sides, as pointed out by Humphry. They are best developed in the adult male. Directly between them in the median line on a level with the upper edge of the orbit is a depression called the glabella. It is the anterior point from which measurements are taken in cerebral topography.
Beneath the superciliary ridges are the frontal air-sinuses, but the size of the sinuses is not necessarily proportional to that of the ridges; they may extend quite far back over the orbit. Fractures of the outer wall of these sinuses not infrequently occur without the inner table being injured. A septum separates one sinus from the other, not always in the median line. The lining membrane of these sinuses is often inflamed and suppurates, discharging pus into the nose. Tumors also grow in them.
At the upper and outer margin of the orbit is the external angular process of the frontal bone. The line of junction or suture between it and the malar bone can be distinctly felt in the living both on the side of the orbit and on the side toward the temple. This is an important landmark in cerebral topography, as it is used to locate the fissure of Sylvius and also the middle meningeal artery. On the upper margin of the orbit at about the junction of its middle and inner thirds is the supra-orbital notch. This can usually be readily felt through the skin. Sometimes it is a complete foramen instead of simply a notch. It is then to be located by feeling on the orbital surface just behind the edge. It transmits the supra-orbital nerve and artery.
The supra-orbital nerve, a branch of the ophthalmic division of the fifth nerve, is sometimes the seat of neuralgia, for which resection of the nerve is performed.
Fig. 54. - Frontal region of a child's skull.
The pain is felt above the orbit radiating from the supra-orbital notch, sometimes as far up as the vertex. Pain is also felt on pressure over the supra-orbital notch. If the entire ophthalmic branch of the fifth nerve is affected, pain is felt in the eyeball and down the side of the nose. The incision in operating may be made at the lower border of the eyebrow, its centre being over the notch. If the notch is not readily felt on the edge of the bony orbit at the junction of the inner and middle thirds, it can be detected by feeling with the tip of the finger on the orbital surface. The incision is made through the fibres of the orbicularis palpebrarum, corrugator supercilii, and frontalis muscles, then through the palpebral ligament immediately below the bony edge of the orbit, and the orbital fat separated with forceps; the nerve is then caught with a hook before it enters the notch, and brought up and removed. Considerable ecchymosis may follow this operation if the accompanying artery is divided. Operations on the ophthalmic division of the fifth nerve have usually been done in connection with removal of the Gasserian ganglion, the other branches being also involved.
Fig. 55. - Supra-orbital nerve and artery.
About a centimetre below the glabella, in the adult skull, is the nasion, or line of junction of the frontal and nasal bones. It is along this frontonasal suture, to one side of the median line, that an anterior meningocele is apt to show itself.
The internal angular process of the frontal bone articulates with the nasal process of the superior maxilla and the lachrymal bones. The line of suture is continuous with the nasion in front and the upper edge of the ethmoid behind. Pus originating in the ethmoidal cells, frontal sinuses, and lachrymal apparatus is apt to point at this locality. The frontal bone is a favorite seat of exostoses.