Frontal bone

Frontal bone
Position of the frontal bone (highlighted in green).
19th Century skull showing sword-blade trauma on frontal bone.
Details
Articulations	Twelve bones: the sphenoid, the ethmoid, the two parietals, the two nasals, the two maxillæ, the two lacrimals, and the two zygomatics
Identifiers
Latin	Os frontale
MeSH	A02.835.232.781.375
TA	A02.1.03.001
FMA	52734
Anatomical terms of bone [edit on Wikidata]

The frontal bone is a bone in the human skull. The bone consists of three portions.^[1] These are the squamous part, the orbital part, and the nasal 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 nose respectively. The name comes from the Latin word frons (meaning "forehead").

Structure

The frontal bone is made up of three parts. These are the squamous part, the orbital part and the nasal part. The squamous part marks the 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 and nasal cavities. The nasal, the smallest, part articulates with the nasal bone and the frontal process of the maxilla to form the root of the nose.^[2]

Borders

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. The posterior borders of the orbital plates are thin and serrated, and articulate with the small wings of the sphenoid. ^[1]

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  Coronal suture separates frontal bone and parietal bones.
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  Sphenofrontal suture separates frontal bone and sphenoid bone.
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  Zygomaticofrontal suture separates frontal bone and zygomatic bones.
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  Nasofrontal suture separates frontal bone and nasal bone.
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  Frontomaxillary suture separates frontal bone and maxilla.

Development

The frontal bone is presumed to be derived from neural crest cells.^[3]

The frontal bone is ossified 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 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.

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  Frontal bone at newborn.
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  Frontal bone at birth.
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  Frontal bone orbital part at newborn.

Other animals

In most vertebrates, 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-mammalian animals it does not form part of the orbital cavity. Instead, in reptiles, bony fish and amphibians it is often separated from the orbits by one or two additional bones not found in mammals. These bones, the prefrontals and postfrontals, together form the upper margin of the eye sockets, and lie to either side of the frontal bones.^[4]

Dinosaurs

The frontal bone is one of the principal paired mid-line bones in dinosaur skulls. This bone is part of the skull roof, which is a set of bones that cover the brain, eyes and nostrils. The frontal makes contact with several other bones in the skull. The anterior part of the bone articulates with the nasal bone and the prefrontal bone. The posterior part of the bone articulates with the postorbital bone and the parietal bone. This bone defines all of part of the upper margin of the orbit.

Additional Images

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  Position of the frontal bone (highlighted in green). Animation.
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  Frontal bone (highlighted in green).
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  Skull showing keyhole gunshot trauma on frontal bone, at Civil War (1861-1865).
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  Inner surface of the frontal bone (highlighted in green). Parietal bones are removed.
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  Inner surface of the frontal bone (highlighted in green). Parietal bones are removed.
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  Outer and inner surface of frontal bone. Animation.
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  Frontal bone. Inferior surface.

See also

Wikimedia Commons has media related to Frontal bones.

• Frontal eminence
• Forehead
• Frontal lobe

References

This article incorporates text in the public domain from the 20th edition of Gray's Anatomy (1918)

External links

• Anatomy photo:23:os-0101 at the SUNY Downstate Medical Center
• Anatomy diagram: 34256.000-1 at Roche Lexicon - illustrated navigator, Elsevier