The orbital or horizontal part of the

frontal bone The frontal bone is a bone in the human skull. The bone consists of two portions.'' Gray's Anatomy'' (1918) These are the vertically oriented squamous part, and the horizontally oriented orbital part, making up the bony part of the forehead, pa ...

(''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 ethmoid bone (; from grc, ἡθμός, hēthmós, sieve) is an unpaired bone in the sku ...

Surfaces

* The inferior surface of each orbital plate is smooth and concave, and presents, laterally, under cover of the

zygomatic process The zygomatic processes are three processes (protrusions) from other bones of the skull which each articulate with the zygomatic bone. The three processes are: * Zygomatic process of frontal bone from the frontal bone * Zygomatic process of maxi ...

, a shallow depression, the lacrimal fossa, for the

lacrimal gland The lacrimal glands are paired exocrine glands, one for each eye, found in most terrestrial vertebrates and some marine mammals, that secrete the aqueous layer of the tear film. In humans, they are situated in the upper lateral region of each o ...

; near the nasal part is a depression, the fovea trochlearis, or occasionally a small trochlear spine, for the attachment of the cartilaginous pulley of the obliquus oculi superior. * The superior surface is convex, and marked by depressions for the convolutions of the

frontal lobes The frontal lobe is the largest of the four major lobes of the brain in mammals, and is located at the front of each cerebral hemisphere (in front of the parietal lobe and the temporal lobe). It is parted from the parietal lobe by a groove be ...

of the

brain The brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It consists of nervous tissue and is typically located in the head ( cephalization), usually near organs for special ...

, 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 In mammalian anatomy, the cribriform plate (Latin for lit. ''sieve-shaped''), horizontal lamina or lamina cribrosa is part of the ethmoid bone. It is received into the ethmoidal notch of the frontal bone and roofs in the nasal cavities. It s ...

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 The ethmoid bone (; from grc, ἡθμός, hēthmós, sieve) is an unpaired bone in the skull that separates the nasal cavity from the brain. It is located at the roof of the nose, between the two orbits. The cubical bone is lightweight due to a ...

, and open on the medial wall of the

orbit In celestial mechanics, an orbit is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an object or position in space such a ...

. *** The anterior canal transmits the

nasociliary nerve The nasociliary nerve is a branch of the ophthalmic nerve, itself a branch of the trigeminal nerve (CN V). It is intermediate in size between the other two branches of the ophthalmic nerve, the frontal nerve and lacrimal nerve. Structure The na ...

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 The sphenoid sinus ...

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. Sinus (anatomy), Sinuses are mucosa-lined airspaces within the bones of the face and skull. Each opens into the anterior part of the corres ...

. ** 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 Puberty is the process of physical changes through which a child's body matures into an adult body capable of sexual reproduction. It is initiated by hormonal signals from the brain to the gonads: the ovaries in a girl, the testes in a b ...

. ** They vary in size in different persons, and are larger in men than in women. ** They are lined by

mucous membrane A mucous membrane or mucosa is a membrane that lines various cavities in the body of an organism and covers the surface of internal organs. It consists of one or more layers of epithelial cells overlying a layer of loose connective tissue. It i ...

, and each communicates with the corresponding

nasal cavity The nasal cavity is a large, air-filled space above and behind the nose in the middle of the face. The nasal septum divides the cavity into two cavities, also known as fossae. Each cavity is the continuation of one of the two nostrils. The nasal ...

by means of a passage called the

frontonasal duct The frontonasal duct is a communication between the frontal air sinuses and their corresponding nasal cavity. The duct is lined by mucous membrane A mucous membrane or mucosa is a membrane that lines various cavities in the body of an organis ...

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