Frontal bone: Difference between revisions

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{{Short description|Bone in the human skull}}

The '''frontal bone''' (''os frontale'') is a [[bone]] in the [[human]] [[skull]] that resembles a [[cockle]]-shell in form, and consists of two portions—a vertical portion, the [[squama]], corresponding with the region of the forehead; and an orbital or horizontal portion, which enters into the formation of the roofs of the [[orbital cavity|orbital]] and [[nasal cavity|nasal cavities]].

{{Infobox bone

| Name = Frontal bone

| Latin = os frontale

| Image2 = File:Frontal bone - animation 02.gif

| Caption2 = Animation of the frontal bone

| Image = Frontal bone lateral3.png

| Caption = Position of the frontal bone (highlighted in green).

| Origins =

| Insertions =

The| frontalArticulations articulates= with twelveTwelve bones: the [[sphenoid bone|sphenoid]], the [[ethmoid bone|ethmoid]], the two parietals[[Parietal bone|parietal]]s, the two [[Nasal bone|nasals]], the two maxillæ[[maxilla]]e, the two [[lacrimal bone|lacrimals]], and the two [[zygomatic bone|zygomatics.]]

}}

In the [[human skull]], the '''frontal bone''' or '''sincipital bone''' is an unpaired [[bone]] which consists of two portions.<ref name="Gray's">''[[Gray's Anatomy]]'' (1918)</ref> These are the vertically oriented [[squamous part of the frontal bone|squamous part]], and the horizontally oriented [[orbital part of frontal bone|orbital part]], making up the bony part of the [[forehead]], part of the bony [[orbital cavity]] holding the eye, and part of the bony part of the [[Human nose|nose]] respectively. The name comes from the Latin word ''frons'' (meaning "[[forehead]]").

== Squama (squama frontalis) ==

=== SurfacesStructure ===

The frontal bone is made up of two main parts. These are the [[squamous part of the frontal bone|squamous part]], and the [[orbital part of frontal bone|orbital part]]. The squamous part marks the vertical, flat, and also the biggest part, and the main region of the [[forehead]]. The orbital part is the horizontal and second biggest region of the frontal bone. It enters into the formation of the roofs of the [[orbital cavity|orbital]] and [[nasal cavity|nasal cavities]]. Sometimes a third part is included as the '''nasal part of the frontal bone''', and sometimes this is included with the squamous part. The nasal part is between the [[brow ridge]]s, and ends in a serrated '''nasal notch''' that articulates with the [[nasal bone]]s inferiorly, and with the [[lacrimal bone|lacrimal]] and [[Maxilla|maxilla bones]] laterally.<ref name="Gray's E-book 479">{{cite book |last1=Standring |first1=Susan |title=Gray's Anatomy E-Book: The Anatomical Basis of Clinical Practice |url=https://books.google.com/books?id=b7FVCgAAQBAJ&q=nasal+notch&pg=PA479 |publisher=Elsevier Health Sciences |language=en |date=7 August 2015|isbn=9780702068515 }}</ref>

The external surface [Fig. 1] of this portion is convex and usually exhibits, in the lower part of the middle line, the remains of the frontal or metopic suture; in infancy this suture divides the bone into two, a condition which may persist throughout life. On either side of this suture, about 3 cm. above the supraorbital margin, is a rounded elevation, the frontal eminence (tuber frontale). These eminences vary in size in different individuals, are occasionally unsymmetrical, and are especially prominent in young skulls; the surface of the bone above them is smooth, and covered by the galea aponeurotica. Below the frontal eminences, and separated from them by a shallow groove, are two arched elevations, the superciliary arches; these are prominent medially, and are joined to one another by a smooth elevation named the glabella. They are larger in the male than in the female, and their degree of prominence depends to some extent on the size of the frontal air sinuses; 28 prominent ridges are, however, occasionally associated with small air sinuses. Beneath each superciliary arch is a curved and prominent margin, the supraorbital margin, which forms the upper boundary of the base of the orbit, and separates the squama from the orbital portion of the bone. The lateral part of this margin is sharp and prominent, affording to the eye, in that situation, considerable protection from injury; the medial part is rounded. At the junction of its medial and intermediate thirds isa notch, sometimes converted into a foramen, the supraorbital notch or foramen, which transmits the supraorbital vessels and nerve. A small aperture in the upper part of the notch transmits a vein from the diploë to join the supraorbital vein. The supraorbital margin ends laterally in the zygomatic process, which is strong and prominent, and articulates with the zygomatic bone. Running upward and backward from this process is a well-marked line, the temporal line, which divides into the upper and lower temporal lines, continuous, in the articulated skull, with the corresponding lines on the parietal bone. The area below and behind the temporal line forms the anterior part of the temporal fossa, and gives origin to the Temporalis muscle. Between the supraorbital margins the squama projects downward to a level below that of the zygomatic processes; this portion is known as the nasal part and presents a rough, uneven interval, the nasal notch, which articulates on either side of the middle line with the nasal bone, and laterally with the frontal process of the maxilla and with the lacrimal. The term nasion is applied to the middle of the frontonasal suture. From the center of the notch the nasal process projects downward and forward beneath the nasal bones and frontal processes of the maxillæ, and supports the bridge of the nose. The nasal process ends below in a sharp spine, and on either side of this is a small grooved surface which enters into the formation of the roof of the corresponding nasal cavity. The spine forms part of the septum of the nose, articulating in front with the crest of the nasal bones and behind with the perpendicular plate of the ethmoid.

== See alsoBorders ==

<center>[[image:Gray_134_-_Frontal_bone._Outer_surface.png]]<br>

The border of the squamous part is thick, strongly serrated, bevelled at the expense of the inner table above, where it rests upon the parietal bones, and at the expense of the outer table on either side, where it receives the lateral pressure of those bones; this border is continued below into a triangular, rough surface, which articulates with the great wing of the [[sphenoid bone|sphenoid]]. The posterior borders of the orbital plates are thin and serrated, and articulate with the small wings of the sphenoid.

'''Figure 1 :''' Frontal bone. Outer surface.</center>

<ref name="Gray's" />

== Development ==

The internal surface [Fig. 2] of the squama is concave and presents in the upper part of the middle line a vertical groove, the sagittal sulcus, the edges of which unite below to form a ridge, the frontal crest; the sulcus lodges the superior sagittal sinus, while its margins and the crest afford attachment to the falx cerebri. The crest ends below in a small notch which is converted into a foramen, the foramen cecum, by articulation with the ethmoid. This foramen varies in size in different subjects, and is frequently impervious; when open, it transmits a vein from the nose to the superior sagittal sinus. On either side of the middle line the bone presents depressions for the convolutions of the brain, and numerous small furrows for the anterior branches of the middle meningeal vessels. Several small, irregular fossæ may also be seen on either side of the sagittal sulcus, for the reception of the arachnoid granulations.

The frontal bone is presumed to be derived from [[neural crest cell]]s.<ref>{{cite journal |last1=Kirby |first1=M. L. |last2=Waldo |first2=K. L. |title=Role of neural crest in congenital heart disease |journal=[[Circulation (journal)|Circulation]] |year=1990 |volume=82 |issue=2 |pages=332–340 |doi=10.1161/01.CIR.82.2.332 |pmid=2197017 |doi-access=free }}</ref>

The frontal bone is [[ossified [Fig. 3]] in membrane from two primary centers, one for each half, which appear toward the end of the second month of [[fetal]] life, one above each [[supraorbital margin]]. From each of these centers, ossification extends upward to form the corresponding half of the [[squama frontalis|squama]], and backwardbackwards to form the orbital plate. The spine is ossified from a pair of secondary centers, on either side of the middle line; similar centers appear in the nasal part and zygomatic processes. At birth the bone consists of two pieces, separated by the frontal suture, which is usually obliterated, except at its lower part, by the eighth year, but occasionally persists throughout life. It is generally maintained that the development of the frontal sinuses begins at the end of the first or beginning of the second year, but Onodi’s researches indicate that development begins at birth. The sinuses are of considerable size by the seventh or eighth year, but do not attain their full proportions until after puberty.

== Orbital or Horizontal Part ==

This portion (''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.

At birth the bone consists of two pieces, separated by the [[frontal suture]], which is usually obliterated by [[Intramembranous ossification]], except at its lower part, by the eighth year, but occasionally persists throughout life. It is generally maintained that the development of the [[frontal sinuses]] begins at the end of the first or beginning of the second year, but may begin at birth. The sinuses are of considerable size by the seventh or eighth year, but do not attain their full proportions until after [[puberty]].

<center>[[image:Gray_135_-_Frontal_bone._Inner_surface.png]]<br>

'''Figure 2 :''' Frontal bone. Inner surface.</center>

=== SurfacesOther animals ===

In most [[vertebrate]]s, the frontal bone is paired, rather than presenting the single, fused structure found in humans (see [[frontal suture]]). It typically lies on the upper part of the head, between the eyes, but in many non-[[mammal]]ian animals it does not form part of the orbital cavity. Instead, in [[reptile]]s, [[Osteichthyes|bony fish]] and [[amphibian]]s it is often separated from the orbits by one or two additional bones not found in mammals. These bones, the [[prefrontal bone|prefrontals]] and [[postfrontal]]s, together form the upper margin of the eye sockets, and lie to either side of the frontal bones.<ref name=VB>{{cite book |author=Romer, Alfred Sherwood|author2=Parsons, Thomas S.|year=1977 |title=The Vertebrate Body |publisher=Holt-Saunders International |___location= Philadelphia, PA|pages= 226–241|isbn= 0-03-910284-X}}</ref>

The inferior surface [Fig. 2] 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, 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 of the brain, 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 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, 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 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. They vary in size in different persons, and are larger in men than in women. 29 They are lined by mucous membrane, and each communicates with the corresponding nasal cavity by means of a passage called the frontonasal duct.

=== BordersDinosaurs ===

The borderfrontal of the squamabone is thick,one stronglyof serrated,the bevelledprincipal atpaired themid-line expensebones ofin thedinosaur innerskulls. table above,This wherebone itis restspart uponof the parietalskull bonesroof, andwhich atis thea expenseset of thebones outerthat tablecover onthe either sidebrain, whereeyes itand receivesnostrils. the lateralThe pressurefrontal ofmakes thosecontact bones;with thisseveral borderother isbones continuedin belowthe intoskull. a triangular,The roughanterior surface,part whichof the bone articulates with the greatnasal wingbone ofand the sphenoid[[Prefrontal bone#In dinosaurs|prefrontal]] bone. The posterior borderspart of the orbitalbone platesarticulates arewith thinthe andpostorbital serrated,bone and articulatethe withparietal bone. This bone defines all of part of the smallupper wingsmargin of the sphenoidorbit.

=== StructureSee also ===

{{Anatomy-terms}}

The squama and the zygomatic processes are very thick, consisting of diploic tissue contained between two compact laminæ; the diploic tissue is absent in the regions occupied by the frontal air sinuses. The orbital portion is thin, translucent, and composed entirely of compact bone; hence the facility with which instruments can penetrate the cranium through this part of the orbit; when the frontal sinuses are exceptionally large they may extend backward for a considerable distance into the orbital portion, which in such cases also consists of only two tables.

* [[Frontal eminence]]

== Ossification ==

* [[Frontal lobe]]

The frontal bone is ossified [Fig. 3] in membrane from two primary centers, one for each half, which appear toward the end of the second month of fetal life, one above each supraorbital margin. From each of these centers ossification extends upward to form the corresponding half of the squama, and backward to form the orbital plate. The spine is ossified from a pair of secondary centers, on either side of the middle line; similar centers appear in the nasal part and zygomatic processes. At birth the bone consists of two pieces, separated by the frontal suture, which is usually obliterated, except at its lower part, by the eighth year, but occasionally persists throughout life. It is generally maintained that the development of the frontal sinuses begins at the end of the first or beginning of the second year, but Onodi’s researches indicate that development begins at birth. The sinuses are of considerable size by the seventh or eighth year, but do not attain their full proportions until after puberty.

== ArticulationsReferences ==

{{Gray's}}

The frontal articulates with twelve bones: the sphenoid, the ethmoid, the two parietals, the two nasals, the two maxillæ, the two lacrimals, and the two zygomatics.

{{Reflist}}

== External links ==

<center>[[image:Gray_136_-_Frontal_bone_at_birth.png]]<br>

{{Commons category|Frontal bones}}

'''Figure 3 :''' Frontal bone at birth.</center>

* {{SUNYAnatomyLabs|23|os|01|01}}

''This article is based on an entry from the 1918 edition of [[Gray's Anatomy]], which is in the [[public ___domain]]. As such, some of the information contained herein may be outdated. Please edit the article if this is the case, and feel free to remove this notice when it is no longer relevant.''

* {{cite web|url=http://www.tk.de/rochelexikon/pics/s34256.000-1.html|title=Anatomy diagram: 34256.000-1|work= Roche Lexicon - illustrated navigator|publisher= Elsevier|archive-url=https://web.archive.org/web/20121227145535/http://www.tk.de/rochelexikon/pics/s34256.000-1.html|archive-date=2012-12-27}}

{{OrbitalBones}}

== See also ==

{{Cranium}}

*[[Bone#Terminology|Bone terminology]]

{{Portal bar|Anatomy}}

*[[Terms for anatomical ___location]]

{{Authority control}}

[[Category:Skeletal system]]

[[Category:Bones of the head and neck]]

[[it:Osso frontale]]

[[Category:Articles containing video clips]]