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Frontal Bone of the Skull - Bone Directory
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Quantity in the Body: 1 Region: Skull |
Anatomical Detail of the frontal bone of the skull- click a part to go to details
Frontal Bone Features and Parts
OVERVIEW
The frontal bone is a single bone located at the front of the vault of
the skull. It has three parts: squamous, nasal and orbital.
Squamous part
The squamous part forms the majority of the bone. Externally, it is
related to the forehead and is considerably convex.
Landmarks include:
Frontal eminence
Supra-orbital margin.
Superciliary arch.
Glabella.
Zygomatic processes.
The posterior border of the squamous part of the bone is markedly
serrated for articulation with the parietal bones at the coronal suture.
Nasal part
The nasal part of the frontal bone is a small, thin plate of bone that
projects antero-inferiorly in the midline between the supra-orbital
margins and forms a small portion of the roof of the nose. Posteriorly,
its serrated free margin, the nasal notch articulates with the nasal
bones, the frontal processes of the maxillary bones, and the lacrimal
bones.
Landmarks include:
Nasal spine.
Orbital parts
The orbital parts of the frontal bone consist of two plates that lie
horizontally to form the roofs (orbital external surfaces) of the orbits
and contribute to the floor (cranial internal surfaces) of the anterior
cranial fossa. The orbital surfaces are concave.
Each plate meets the squamous part of the frontal bone anteriorly at the
supra-orbital margin. Landmarks include:
Ethmoid notch.
Trochlear fovea.
Lacrimal fossa.
Posterior ethmoid foramen.
Medially the orbital plates articulate with the cribriform plate of the
ethmoid bone at the fronto-ethmoidal (cribrofrontal) suture. The
anterior ethmoidal canal opens into this suture behind the crista galli.
Posterioly the orbital plates are serrated for articulation with the
lesser wing of the sphenoid bone at the fronto-sphenoidal suture.
Frontal sinuses
Within the frontal bone, above and behind the superciliary arches are
two cavities, termed the frontal air sinuses.
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anterior ethmoidal foramen
On the superior aspect of the ethmoidal labyrinth, are two grooves found
between the exposed ethmoidal air cells of the orbital plate, the
anterior and posterior grooves. On articulation with the frontal bone
the anterior ethmoidal groove is completed to form the anterior
ethmoidal canal. The opening of this canal is the anterior ethmoidal
foramen.
Transmit
This canal transmits the anterior ethmoidal nerves and vessels.
Click the image to enlarge it.
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| depressions of arachnoid granulations (granular foveolae)
The depressions of the arachnoid granulations are found on the internal surface of the calvaria, either side of the groove for the superior sagittal venous sinus. GO BACK TO LIST OF DETAILS |
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ethmoidal notch
The ethmoidal notch separates the orbital plates of the frontal bone from each other; occasionally they join posteriorly. The ethmoidal notch houses the cribriform plate of the ethmoid. The margins of the ethmoidal notch articulate with the lateral masses (labyrinths) of the ethmoid bone and thereby complete the roofs of the ethmoidal air cells. Impressions of the air cells and the grooves related to the anterior and posterior ethmoidal nerves and vessels can be seen on this margin. These grooves become canals with articulation of the ethmoidal labyrinth. The frontal sinuses can be seen around the anterior portion of the ethmoidal notch. GO BACK TO LIST OF DETAILS |
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foramen cecum
The foramen cecum is a depression located on the dorsum of the tongue, at the posterior end of the midline groove. From it two shallow grooves known as the terminal sulcus (sulci terminalis) run anterolateral to reach the side of the tongue. GO BACK TO LIST OF DETAILS |
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frontal crest
The internal surface of the frontal bone is concave and on the upper median part is the vertical groove for the sagittal sinus; its edges unite anteriorly as a prominent projection called the frontal crest. Attachments The crest provides attachment for a sheet of meninges, the falx cerebri, which passes between the two cerebral hemispheres of the brain. GO BACK TO LIST OF DETAILS |
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frontal eminence (tuberosity)
The rounded frontal eminences or tuberosities are the most prominent bulges found on the squamous part of the frontal bone. They are found anteriorly above each superciliary arch, their prominence varying; they are usually most apparent on skulls of the young and female adults. GO BACK TO LIST OF DETAILS |
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frontal sinus
Within the frontal bone are two funnel-shaped cavities, termed the ' frontal air sinuses '. They lie above and behind the superciliary arches immediately above the roof of the nasal cavity and may extend into the medial part of the roof of the orbit. In such cases, a thin layer of bone separates the sinus from the floor of the cranial cavity and from the roof of the orbit. Both the anterior and posterior walls of the sinuses are composed of diploe bone, however, the posterior wall, which separates the frontal sinus from the anterior cranial fossa, is much thinner. The floor of the sinus also functions as a portion of the orbital roof. The frontal sinuses are frequently unequal in size and the larger sinus may sometimes extend across the midline. The sinuses are separated by a bony septum, which is often asymmetrically positioned, and the sinus may be partially subdivided by additional septa. The anterior ethmoidal air cells may encroach onto the frontal sinuses. The sinuses have a mucous membrane lining and are connected and drain into the middle nasal meatus of the lateral wall of the nasal fossa. The point of drainage varies and occurs either through a simple opening or as a channel termed the 'frontonasal duct'. The frontal sinus can drain directly into the ethmoidal infundibulum of the hiatus semilunaris. The ethmoidal infundibulum is normally blind-ended and the frontal sinus drains in front of or above the infundibulum. The sinuses are not present at birth and only reach their full capacity after puberty. They are irregular in size but are usually larger in males. GO BACK TO LIST OF DETAILS |
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glabella
On the external surface of the frontal bone, between the superciliary arches is a smooth raised elevation, termed the glabella. The prominence of the superciliary arches and the adjoining glabella is greater in males and is usually dependent on the size of the frontal sinuses. GO BACK TO LIST OF DETAILS |
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grooves for meningeal vessels
The internal surface of the frontal bone shows impressions of the cerebral gyri and small grooves for the meningeal vessels. GO BACK TO LIST OF DETAILS |
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impressions of cerebral gyri
The internal surface of the frontal bone shows impressions of the cerebral gyri and small groves for the meningeal vessels. GO BACK TO LIST OF DETAILS |
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lacrimal fossa
In the antero-lateral corner of the roof of each orbit (orbital surfaces of the orbital plates of the frontal bone) is a lacrimal fossa that houses the orbital part (larger part) of the lacrimal gland. GO BACK TO LIST OF DETAILS |
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nasal spine
The nasal part of the frontal bone is a small, thin plate of bone that projects antero-inferiorly behind the nasal bones and maxillary frontal processes and terminates in a sharp nasal spine. This spine makes a minor contribution to the nasal septum and articulates anteriorly with the crest of the nasal bone and posteriorly with the perpendicular plate of the ethmoid bone. GO BACK TO LIST OF DETAILS |
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posterior ethmoidal foramen
The posterior ethmoidal foramina are found in the fronto-ethmoidal suture, between the orbital parts of the frontal bone and the ethmoid bone. Transmit These foramina transmit the posterior ethmoidal nerves and vessels. GO BACK TO LIST OF DETAILS |
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sulcus for sagittal sinus
The sulcus of the sagittal sinus is a large groove running along the median sagittal plane on the internal surface of the frontal bone. The falx cerebri is attached to the skull along the lateral margins of the sagittal sulcus. GO BACK TO LIST OF DETAILS |
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superciliary arch
Just above the supra-orbital margins are the curved ridges of the superciliary arches. They meet above the nose to form another ridge called the glabella. The prominence of the superciliary arches and the adjoining glabella is greater in males and is usually dependent on the size of the frontal sinuses. GO BACK TO LIST OF DETAILS |
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supra-orbital margin
Inferiorly the squamous and orbital parts of the frontal bone meet to form the supra-orbital margins. They form the prominent upper margins of the orbits. The lateral two-thirds of each supra-orbital margin is sharp whereas the medial third is rounded. At the junction is the supra-orbital notch, which transmits the supra-orbital nerve and vessels from the orbit onto the forehead. Laterally the supra-orbital margins project laterally as the zygomatic processes of the frontal bone, which articulate with the frontal processes of the zygomatic bones. GO BACK TO LIST OF DETAILS |
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supra-orbital notch (supra-orbital foramen)
On the frontal bone the lateral two-thirds of each supra-orbital margin is sharp whereas the medial third is rounded and at this junction is the supra-orbital notch or foramen. Transmit The supra-orbital notch transmits the supra-orbital nerve and vessels from the orbit onto the forehead. GO BACK TO LIST OF DETAILS |
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temporal surface
The temporal surface is the area of the frontal bone postero-inferior to the temporal lines that forms the antero-superior portion of the temporal fossa. Attachments It gives attachment to the anterior part of the temporalis muscle. GO BACK TO LIST OF DETAILS |
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trochlear fovea (trochlear spine or tubercle)
In the antero-medial corner of the orbital (external) surfaces of each of the orbital plates of the frontal bone is a depression or tubercle, the trochlear fovea or tubercle. Attachments It marks the site of attachment of the fibrocartilaginous pulley, trochlea, through which the superior oblique muscle of the eye passes. GO BACK TO LIST OF DETAILS |
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zygomatic process
The zygomatic processes of the frontal bone project laterally from the supra-orbital margins to articulate with the frontal processes of the zygomatic bones at the frontozygomatic sutures, forming the zygomatic arches. GO BACK TO LIST OF DETAILS |
The information contained on this site is for educational purposes only and should not be taken as expert advice.
This page was last updated 3/25/2010
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