In thehuman skull, thefrontal bone orsincipital bone is an unpairedbone which consists of two portions.[1] These are the vertically orientedsquamous part, and the horizontally orientedorbital part, making up the bony part of theforehead, part of the bonyorbital cavity holding the eye, and part of the bony part of thenose respectively. The name comes from the Latin wordfrons (meaning "forehead").
The frontal bone is made up of two main parts. These are thesquamous part, and theorbital part. The squamous part marks the vertical, flat, and also the biggest part, and the main region of theforehead. The orbital part is the horizontal and second biggest region of the frontal bone. It enters into the formation of the roofs of theorbital andnasal cavities. Sometimes a third part is included as thenasal part of the frontal bone, and sometimes this is included with the squamous part. The nasal part is between thebrow ridges, and ends in a serratednasal notch that articulates with thenasal bones inferiorly, and with thelacrimal andmaxilla bones laterally.[2]
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 thesphenoid. The posterior borders of the orbital plates are thin and serrated, and articulate with the small wings of the sphenoid.[1]
The frontal bone isossified in membrane from two primary centers, one for each half, which appear toward the end of the second month offetal life, one above eachsupraorbital margin. From each of these centers, ossification extends upward to form the corresponding half of thesquama, and backwards 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 thefrontal suture, which is usually obliterated byIntramembranous ossification, except at its lower part, by the eighth year, but occasionally persists throughout life. It is generally maintained that the development of thefrontal 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 afterpuberty.
In mostvertebrates, the frontal bone is paired, rather than presenting the single, fused structure found in humans (seefrontal 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, inreptiles,bony fish andamphibians it is often separated from the orbits by one or two additional bones not found in mammals. These bones, theprefrontals andpostfrontals, together form the upper margin of the eye sockets, and lie to either side of the frontal bones.[4]
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 theprefrontal 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.
