Frontal sinus

The frontal sinuses, situated behind the superciliary arches, are rarely symmetrical, and the septum between them frequently deviates to one or other side of the middle line.

Their average measurements are as follows: height, 3 cm.; breadth, 2.5 cm.; depth from before backward, 2.5 cm.

Each opens into the anterior part of the corresponding middle meatus of the nose through the frontonasal duct which traverses the anterior part of the labyrinth of the ethmoid. These structures then open into the hiatus semilunaris in the middle meatus.

The mucuous membrane in this sinus is innervated by the supraorbital nerve and supplied by the supraorbital artery and anterior ethmoidal artery.

Absent at birth, they are generally fairly well developed between the seventh and eighth years, but only reach their full size after puberty.