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.
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 max ...
, 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 or ...
; 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 betwe ...
of the
brain
A brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as vision. It is the most complex organ in a ve ...
, and faint grooves for the meningeal branches of the
ethmoidal vessels.
** The
ethmoidal notch 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 supp ...
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.
** 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 as ...
.
*** 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 and vessels.
* In front of the ethmoidal notch, on either side of the frontal spine, are the openings of the
frontal air sinuses.
** 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 bo ...
.
** 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 human nose, 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. ...
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. The duct empties into the nasal cavity middle nasal meatus through the infundibulum of the semil ...
.
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
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Bones of the head and neck