Bone in the human skull
In the
human skull
, the
frontal bone
or
sincipital bone
is a unpaired
bone
which consists of two portions.
[1]
These are the vertically oriented
squamous part
, and the horizontally oriented
orbital 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
[
edit
]
The frontal bone is made up of two main parts. These are the
squamous part
, and the
orbital part
. The squamous part marks the vertical, 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
. Sometimes a third part is included as the
nasal part of the frontal bone
, and sometimes this is included with the squamous part. The nasal part is between the
brow ridges
, and ends in a serrated
nasal notch
that articulates with the
nasal bones
inferiorly, and with the
lacrimal
and
maxilla bones
laterally.
[2]
Borders
[
edit
]
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]
Development
[
edit
]
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 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 the
frontal suture
, which is usually obliterated by
Intramembranous ossification
, 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
.
Other animals
[
edit
]
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
[
edit
]
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.
See also
[
edit
]
References
[
edit
]
This article incorporates text in the
public domain
from
page 135
of the 20th edition of
Gray's Anatomy
(1918)
External links
[
edit
]