The orbital or horizontal part of the frontal bone (''pars orbitalis'') consists of two thin triangular plates, the orbital plates, which form the vaults of the orbits, and are separated from one another by a median gap, the

ethmoidal notch The ethmoidal notch separates the two orbital plates; it is quadrilateral, and filled, in the articulated skull, by the cribriform plate of the ethmoid. The margins of the notch present several half-cells which, when united with corresponding hal ...

Surfaces

* The inferior surface of each orbital plate is smooth and concave, and presents, laterally, under cover of the zygomatic process, a shallow depression, the lacrimal fossa, for the lacrimal gland; near the nasal part is a depression, the

fovea trochlearis The trochlear fovea is a slight depression on the anteromedial orbital surface of the orbital plate of the frontal bone. Attached to the trochlear fovea is the trochlea of the superior oblique muscle The superior oblique muscle, or obliquus ocu ...

, or occasionally a small trochlear spine, for the attachment of the cartilaginous pulley of the

obliquus oculi superior The superior oblique muscle, or obliquus oculi superior, is a fusiform muscle originating in the upper, medial side of the orbit (i.e. from beside the nose) which abducts, depresses and internally rotates the eye. It is the only extraocular musc ...

. * The superior surface is convex, and marked by depressions for the convolutions of the frontal lobes of the brain, and faint grooves for the meningeal branches of the ethmoidal vessels. ** The

separates the two orbital plates; it is quadrilateral, and filled, in the articulated skull, by the cribriform plate of the ethmoid. *** The margins of the notch present several half-cells which, when united with corresponding half-cells on the upper surface of the ethmoid, complete the

ethmoidal air cells The ethmoid sinuses or ethmoid air cells of the ethmoid bone are one of the four paired paranasal sinuses. The cells are variable in both size and number in the lateral mass of each of the ethmoid bones and cannot be palpated during an extraoral e ...

. ** Two grooves cross these edges transversely; they are converted into the anterior and posterior ethmoidal canals by the ethmoid, and open on the medial wall of the orbit. *** The anterior canal transmits the nasociliary nerve and anterior ethmoidal vessels, *** the posterior, the posterior

ethmoidal nerve The ethmoidal nerves, which arise from the nasociliary nerve, supply the ethmoidal cells; the posterior branch leaves the orbital cavity through the posterior ethmoidal foramen and gives some filaments to the sphenoidal sinus. There are two ethmoid ...

and vessels. * In front of the ethmoidal notch, on either side of the frontal spine, are the openings of the

frontal air sinuses The frontal sinuses are one of the four pairs of paranasal sinuses that are situated behind the brow ridges. Sinuses are mucosa-lined airspaces within the bones of the face and skull. Each opens into the anterior part of the corresponding middle na ...

. ** These are two irregular cavities, which extend backward, upward, and lateralward for a variable distance between the two tables of the skull; they are separated from one another by a thin bony septum, which often deviates to one or other side, with the result that the sinuses are rarely symmetrical. ** Absent at birth, they are usually fairly well-developed between the seventh and eighth years, but only reach their full size after puberty. ** They vary in size in different persons, and are larger in men than in women. ** They are lined by mucous membrane, and each communicates with the corresponding nasal cavity by means of a passage called the frontonasal duct.

Additional images

Image:Orbital_bones.png, The seven bones which articulate to form the orbit. Image:Gray192.png, Medial wall of left orbit. File:Slide18hhhh.JPG, Orbital part of frontal bone File:Slide3jjjj.JPG, Orbital part of frontal bone

References

External links

* {{Authority control Bones of the head and neck