Os frontal 319204 30785922 2008-06-19T11:17:45Z Korr 10177 {{ébauche|médecine}} [[Image:Gray190.png|thumb|430px|]] L''''os frontal''' est un [[os impair]], plat, galbé et partiellement [[pneumatisé]] participant à la formation du crâne et de la face. Il s'articule avec l'[[os Éthmoïde|os éthmoïde]], les [[os maxillaire]]s, les [[Os pariétal|os pariétaux]], les [[Os nasal|os nasaux]], l'[[os sphénoïde]] et les [[Os lacrymal|os lacrymaux]]. Il se compose d'une '''[[écaille]]''' formant la voute du crâne et d'une [[lame orbitaire]] qui s'articule avec le [[massif facial]] tout en soutenant la [[fosse crânienne antérieure]]. L'os frontal est creusé de deux [[Sinus (anatomie)|sinus]] frontaux. <!-- L''''os frontal''' est un os participant à la formation du crâne et de la face.<br> Il est formé de 2 parties : *une verticale, l''''écaille''' (ou '''partie squameuse'''), qui correspond à la région du front *la '''lame orbitaire''', qui entre dans la composition du toit des orbites et des cavités nasales. == Écaille== Également appelée '''partie squameuse'''. C'est la partie verticale de l'os. === Surfaces=== [[Image:Gray_134_-_Frontal_bone._Outer_surface.png|thumb|300px|Figure 1: Frontal bone, outer surface]] La '''face exocrânienne''' [Fig. 1] de l'écaille est convexe et comporte habituellement, dans la partie basse de la ligne médiane, les restes de la suture frontale (ou suture métopique) ; dans l'enfance, cette suture divise l'os en 2, ceci pouvant parfois persister toute la vie chez certaines personnes. # 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 is a 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]]. 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]]. == 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]]. [[Image:Gray_135_-_Frontal_bone._Inner_surface.png|thumb|300px|Figure 2: Frontal bone, inner surface]] === Surfaces === # 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 plate]]s; 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. # They are lined by [[mucous membrane]], and each communicates with the corresponding [[nasal cavity]] by means of a passage called the [[frontonasal duct]]. === Borders === The border of the [[squama]] 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]]. The posterior borders of the orbital plates are thin and serrated, and articulate with the small wings of the sphenoid. === Structure === 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]]. == Ossification == [[Image:Gray_136_-_Frontal_bone_at_birth.png|thumb|300px|Figure 3: Frontal bone at birth]] 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. == Articulations == The frontal [[articulates]] with twelve bones: the [[sphenoid]], the [[ethmoid]], the two [[parietal]]s, the two [[nasals]], the two [[maxillæ]], the two [[lacrimals]], and the two [[zygomatics]]. {{Gray's}} {{Template:HumanBones}} == See also == *[[Bone#Terminology|Bone terminology]] *[[Terms for anatomical location]]--> {{Squelette humain}} {{Portail médecine}} [[Catégorie:Sinus (médecine)|Os frontal]] [[Catégorie:Crâne|Frontal]] [[ar:عظم جبهي]] [[ca:Os frontal]] [[de:Stirnbein]] [[en:Frontal bone]] [[es:Hueso frontal]] [[gl:Frontal (óso)]] [[it:Osso frontale]] [[ja:前頭骨]] [[ko:이마뼈]] [[la:Os frontale]] [[lt:Kaktikaulis]] [[lv:Pieres kauls]] [[mk:Челна коска]] [[pl:Kość czołowa]] [[pt:Osso frontal]] [[ru:Лобная кость]] [[sk:Čelová kosť]] [[sl:Čelnica]] [[sv:Pannben]] [[th:กระดูกหน้าผาก]] [[tr:Os frontale]] [[uk:Лобна кістка]] [[zh:额骨]]