For the sake of study, we can divide this bone as having four angles, four borders and two surfaces.

Surfaces:

The external surface is curved, smooth in appearance and is convex. Following are important features that are observed at the external surface of the bones:

• The parietal eminence is a rounded prominence, located near the middle of the bone.

• The superior and inferior temporal lines are two arched lines that are present on the sides of skull, crossing the middle of the parietal bone in a curved manner.

• The parietal foramina (for a vein going to superior sagittal sinus and sometimes the occipital artery) are two small openings present on either side of the sagittal suture, at the rear (posterior) end of the bone.

The internal surface is concave in appearance. There are depressions and numerous impressions are present on its surface that corresponds to the convulsions of brain and blood vessels.

• Along the upper margin, groove is present. It is an impression because of the sinuses of the brain running through it.

• The internal openings of parietal foramina are visible inside this groove.

Borders:

Following four borders are present on each parietal bone:

• The occipital border is present posteriorly. At this point, the parietal bone articulates with the occipital bone, that is why it is called occipital border. The point of articulation of these two bones is marked by the lambdoid suture. The point of union of lambdoidal suture with sagittal suture is called lambda.

• The frontal border is present anteriorly. It is that border which articulates with the frontal bone, hence the name called frontal border. The point of articulation of these two bones is marked by the coronal suture. The point of union of sagittal suture and coronal suture is called bregma.

• The sagittal border is present medially. It is the point where two parietal bones articulate. It is the longest and thickest of all borders. The point of union of the two parietal bones is marked by sagittal suture.

• The squamous border is that border of parietal bone which is present laterally. It is further divided into three parts;

• The anterior part (it is overlapped by the sphenoid bones’ greater wing)

• The middle part (it is overlapped by the temporal bone’s squamous)

• The posterior part (makes joint with the mastoid process of temporal bone)

Angles:

Following are the four angles each parietal bone:

• The frontal angle

• The occipital angle

• The sphenoidal angle

• The mastoid angle

SOME CLINICAL ASPECTS