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72 ANATOMY.

Frontal Bone.

The Frontal Bone (Fig. 27) is symmetrical in form— /. e. equal
on both sides of the median line of the head. It is situated in front
of the two parietal and a portion of the sphenoid bones, and above the
malar, lachrymal, nasal, part of the sphenoid, and ethmoid bones.
Though it is a true cranial bone, it forms that portion of the face called
the forehead, and is included in the " facial region." Its ascending
portion forms the anterior boundary and part of the roof of the brain-

FiG. 27.

Wm Internal Ejoier^iaf
ml Angular jiroc. Angular hroe
A^asal I S/i/n
Frontal Bone, outer surface.

case. Its horizontal portion forms nearly the entire floor of the anterior
fossa of the skull and the roof^ of the orbits. Laterally, the bone also
enters into the formation of the tcm])oral fossa. It is composed prin-
ci])ally of coin])act tissue, and is divided into an ascending and a hori-
zontal portion.
The ascending portion commences at the supraorbital arch, and
extends upward and backward until it articulates with the parietal
bones. It has two surfaces, an external and an internal, and is divided
in the median line by a slight ridge. In young subjects before this
ridge is developed a suture occupies this line.