Frontal Bone

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 and nasal cavities.

Squama (squama frontalis)

Surfaces

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.

Figure 1 : Frontal bone. Outer surface.

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.

Figure 2 : Frontal bone. Inner surface.

Ossification

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 parietals, the two nasals, the two maxillæ, the two lacrimals, and the two zygomatics.

Figure 3 : Frontal bone at birth.

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.

Non-Fiction Usage: Frontal Bone

Subject	Topic	Quote
Health		The coronal suture is the fibrous joint that unites the frontal bone with the two parietal bones of the skull. (references)
		TRIGONOCEPHALY is the premature fusion of the metopic suture (part of the frontal suture which joins the two halves of the frontal bone of the skull) in which a V-shaped abnormality occurs at the front of the skull. (references)
Source: compiled by the editor from ICON Group International, Inc.; see credits.

Modern Translation: Frontal Bone

Language		Translations for "frontal bone"; alternative meanings/domain in parentheses.
Arabic		‏عظم جبهي. (various references)

Finnish		otsaluu. (various references)

French		frontal (frontlet). (various references)

Manx		craue yn eddin, craue baaishag. (various references)

Pig Latin		ontalfray onebay

Turkish		alın kemiği. (various references)
Source: compiled by the editor from various translation references.

Anagrams: Frontal Bone

Scrabble® Enable2K-Verified Anagrams
	Words within the letters "a-b-e-f-l-n-n-o-o-r-t"
	-2 letters: afternoon.
	-3 letters: bannerol, barefoot, fontanel, nonlabor.
	-4 letters: baronet, baronne, bloater, borneol, floater, footler, frontal, fronton, lantern, notable, ortolan, reboant, refloat.
	-5 letters: antler, atoner, banner, bannet, banter, befool, boatel, boater, bolero, bolter, bonnet, borane, borate, boreal, enroot, etalon, fabler, falter, fanner, florae, floret, foetal, foetor, folate, fontal, footer, footle, labret, lanner, learnt, loafer, loaner, lobate.
	Words containing the letters "a-b-e-f-l-n-n-o-o-r-t"
	+3 letters: nonforfeitable.
Source: compiled by the editor from various references; see credits. SCRABBLE® is a registered trademark. All intellectual property rights in and to the game are owned in the U.S.A and Canada by Hasbro Inc., and throughout the rest of the world by J.W. Spear & Sons Limited of Maidenhead, Berkshire, England, a subsidiary of Mattel Inc. Mattel and Spear are not affiliated with Hasbro.