Surfaces of the parietal bone
Anatomically, the parietal bone is a classic flat bone with two main surfaces that differ radically from each other in their relief.
External surface (facies externa) has a pronounced convex shape. It features structures that serve as landmarks during palpation and the study of the skull:
- Parietal eminence (tuber parietale, or eminentia parietalis) is the most prominent part of the external surface.
- Superior temporal line (linea temporalis superior) and inferior temporal line (linea temporalis inferior) are arch-shaped markings on the external surface.
Internal surface (facies interna), on the other hand, is concave. Its relief is due to the adjacency of the meninges and blood vessels. The following formations can be found on it:
- Sulcus for the superior sagittal sinus (sulcus sinus sagittalis superioris).
- Sulcus for the sigmoid sinus (sulcus sinus sigmoidei).
- Sulcus for the 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 of them is named according to the structure it contacts:
- Sagittal border (margo sagittalis) is the upper border of the bone. It articulates with the corresponding paired border of the opposite parietal bone, forming the median sagittal suture.
- Frontal border (margo frontalis) is the anterior border directed toward the frontal bone. In its upper part, it transitions into the frontal angle.
- Occipital border (margo occipitalis) is the posterior border of the bone, facing the occipital bone and forming the occipital angle.
- Squamous border (margo squamosus) is the lower border that articulates with the temporal bone.
Angles of the parietal bone
The convergence points of the bone's borders form four angles. Knowledge of these angles is critical for understanding the topography of the skull as a whole:
- Frontal angle (angulus frontalis) is located anterosuperiorly and is characterized by a sharp shape.
- Occipital angle (angulus occipitalis) is located posterosuperiorly; in shape, it is less acute compared to the frontal angle.
- Sphenoidal angle (angulus sphenoidalis) is the anteroinferior angle.
- Mastoid angle (angulus mastoideus) is the posteroinferior angle of the bone.
Briefly: answers to topical questions
Which bones does the parietal bone articulate with along each of its borders?
The parietal bone articulates with four cranial bones along each of its borders.
- Sagittal border (margo sagittalis) articulates with the opposite parietal bone, forming the sagittal suture.
- Frontal border (margo frontalis) articulates with the frontal bone via the coronal suture.
- Occipital border (margo occipitalis) articulates with the occipital bone via the lambdoid suture.
- Squamous border (margo squamosus) articulates with the temporal bone via the squamous suture.
Which vessels leave impressions on the internal surface of the parietal bone?
The internal surface of the parietal bone features grooves associated with the superior sagittal sinus, the sigmoid sinus, and the middle meningeal artery:
- Superior sagittal sinus — sulcus for the superior sagittal sinus (sulcus sinus sagittalis superioris).
- Sigmoid sinus — sulcus for the sigmoid sinus (sulcus sinus sigmoidei).
- Middle meningeal artery — sulcus for the middle meningeal artery (sulcus arteriae meningeae mediae).
The names of the borders and angles of the parietal bone strictly correspond to the neighboring cranial bones: frontal (anteriorly), occipital (posteriorly), sphenoidal and temporal (inferiorly).
Class and exam questions
What type of bone is the parietal bone?
This is a paired flat bone of the skull.
Which venous sinus sulci are located on the internal surface?
The sulcus for the superior sagittal sinus and the sulcus for the sigmoid sinus are located on the internal surface.
Which border of the parietal bone forms the sagittal suture?
The sagittal suture is formed by the articulation of the sagittal border of one parietal bone with the sagittal border of the paired parietal bone.
What else to study on this topic
- Formation of the sagittal suture
- Sulcus for the middle meningeal artery
- Superior and inferior temporal lines
- Parietal eminence as an anatomical landmark
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