Surfaces of the Parietal Bone
Anatomically, the parietal bone is a classic flat bone featuring two primary surfaces that differ significantly in their bony landmarks.
External surface (facies externa) is markedly convex. It features key landmarks useful for palpation and skull identification:
- Parietal eminence (tuber parietale, or eminentia parietalis) — the most prominent part of the external surface.
- Superior temporal line (linea temporalis superior) and inferior temporal line (linea temporalis inferior) — curved ridges on the external surface.
Internal surface (facies interna), conversely, is concave. Its relief is shaped by the impressions of the meninges and blood vessels. Key features include:
- Groove for superior sagittal sinus (sulcus sinus sagittalis superioris).
- Groove for sigmoid sinus (sulcus sinus sigmoidei).
- Groove for middle meningeal artery (sulcus arteriae meningeae mediae).
- Inconstant parietal foramina (foramen parietale), which are not present in every specimen.
Borders of the Parietal Bone
To articulate properly with neighboring cranial bones, the parietal bone has four specialized borders, each named after the adjacent structure:
- Sagittal border (margo sagittalis) — the superior border. It articulates with the contralateral parietal bone to form the midline sagittal suture.
- Frontal border (margo frontalis) — the anterior border, facing the frontal bone. Superiorly, it transitions into the frontal angle.
- Occipital border (margo occipitalis) — the posterior border, facing the occipital bone and forming the occipital angle.
- Squamous border (margo squamosus) — the inferior border, which articulates with the temporal bone.
Angles of the Parietal Bone
The junctions of the borders form four angles, which are critical for understanding overall cranial topography:
- Frontal angle (angulus frontalis) — located anterosuperiorly, characterized by an acute shape.
- Occipital angle (angulus occipitalis) — located posterosuperiorly, less acute than the frontal angle.
- Sphenoidal angle (angulus sphenoidalis) — anteroinferior angle.
- Mastoid angle (angulus mastoideus) — posteroinferior angle.