Frontal bone

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Frontal bone

19th Century skull showing sword-blade trauma on frontal bone.

Position of the frontal bone (highlighted in green).
Latin	Os frontale
Gray's	p.135
Articulations	Twelve bones: the sphenoid, the ethmoid, the two parietals, the two nasals, the two maxillæ, the two lacrimals, and the two zygomatics
MeSH	Frontal+Bone
TA	A02.1.03.001
FMA	FMA:52734

The frontal bone or os frontis is a bone in the human skull. The name comes from the Latin word frons (meaning "forehead"). The bone resembles a cockleshell in form, and consists of three portions:^[1]

a large vertical portion, the squama frontalis, corresponding with the region of the forehead.
an orbital or horizontal portion, the pars orbitalis, which enters into the formation of the roofs of the orbital and nasal cavities.
a nasal portion, it articulates with the nasal bones and the frontal process of the maxilla to form the root of the nose.

Structure

Borders

The border of the squama frontalis 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]

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

Development

The frontal bone is presumed to be derived from neural crest cells.^[2]

Figure 3: Frontal bone at birth

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 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.

In 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.^[3]

In 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

Position of the frontal bone (highlighted in green). Animation.
Frontal bone (highlighted in green).
Frontal bone at the top.
Frontal bone (highlighted in green).
Skull showing keyhole gunshot trauma on frontal bone, at Civil War (1861-1865).
Exploded skull. Frontal bone is at the center top.
Frontal bone. Outer surface.
Frontal bone at newborn.
Frontal bone at birth.
Inner surface of the frontal bone (highlighted in green). Parietal bones are removed.
Inner surface of the frontal bone (highlighted in green). Parietal bones are removed.
Inner surface of the frontal bone (highlighted in red).
Frontal bone orbital part at newborn.
Inner surface of the frontal bone (highlighted in blue at the top).
Outer and inner surface of frontal bone. Animation.
Sagittal section of skull. Frontal bone is highlighted in blue, at center left.
Frontal bone. Inferior surface.
Frontal bone. Inferior surface.
Cephalic extremity.Original mummification.
Cephalic extremity.Original mummification.

References

This article incorporates text from a public domain edition of Gray's Anatomy.

↑ 1.0 1.1 Gray's Anatomy (1918). (See infobox)
↑ Kirby, ML; Waldo, KL. Circulation (1990) 82:332-340.
↑ Romer, Alfred Sherwood; Parsons, Thomas S. (1977). The Vertebrate Body. Philadelphia, PA: Holt-Saunders International. pp. 226–241. ISBN 0-03-910284-X.

External links

v t e The Bones which form the Orbit

Frontal bone Zygomatic bone Maxillary bone Sphenoid bone Ethmoid bone Palatine bone Lacrimal bone

Bones of head and neck: the neurocranium of the skull (TA A02.1.01–07, GA 2.129–155)

Occipital

Squama	external Inion/External occipital protuberance External occipital crest Nuchal lines planes Occipital Nuchal internal Cruciform eminence Internal occipital protuberance Sagittal sulcus Internal occipital crest Groove for transverse sinus

Lateral parts	Condyle Condyloid fossa Condylar canal Hypoglossal canal jugular Jugular process Jugular tubercle

Basilar part	Pharyngeal tubercle Clivus

Other	Foramen magnum Basion Opisthion

Parietal

Frontal

Squama	Frontal suture Frontal eminence external Superciliary arches Glabella foramina Supraorbital Cecum Zygomatic process internal Sagittal sulcus Frontal crest

Orbital part	Ethmoidal notch Fossa for lacrimal gland Trochlear fovea Frontal sinus Frontonasal duct

Temporal

Squama	Articular tubercle Suprameatal triangle Mandibular fossa Petrotympanic fissure Zygomatic process

Mastoid part	Mastoid foramen Mastoid process (Mastoid cells) Mastoid notch Occipital groove Sigmoid sulcus Mastoid antrum (Aditus)

Petrous part	Carotid canal Facial canal (Hiatus) Internal auditory meatus Cochlear aqueduct Stylomastoid foramen fossae Subarcuate fossa Jugular fossa canaliculi Inferior tympanic Mastoid Styloid process Petrosquamous suture (note: ossicles in petrous part, but not part of temporal bone)

Tympanic part	Suprameatal spine

Sphenoid

Surfaces	Superior surface: Sella turcica Dorsum sellae Tuberculum sellae Hypophysial fossa Posterior clinoid processes Ethmoidal spine Chiasmatic groove Middle clinoid process Petrosal process Clivus Lateral surface: Carotid groove Sphenoidal lingula Anterior surface: Sphenoidal sinuses

Great wings	foramina Rotundum Ovale Vesalii Spinosum Spine Infratemporal crest Sulcus for auditory tube

Small wings	Superior orbital fissure Anterior clinoid process Optic canal

Pterygoid processes	fossae Pterygoid Scaphoid pterygoid plates Lateral Medial Pterygoid canal Hamulus

Other	Body Sphenoidal conchae

Ethmoid

Plates	Cribriform plate Crista galli Olfactory foramina Perpendicular plate

Surfaces	Lateral surface Orbital lamina Uncinate process Medial surface Superior nasal concha Superior meatus Middle nasal concha Middle meatus

Labyrinth	Ethmoid sinus ethmoidal foramina Posterior Anterior

M: BON/CAR

anat (c/f/k/f, u, t/p, l)/phys/devp/cell

noco/cong/tumr, sysi/epon, injr

proc, drug (M5)

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