Which bones feature the sulcus?
The sigmoid sulcus is marked on the inner surface of three cranial bones:
- Parietal bone (Os parietale) is a paired flat bone. The sulcus is located on its concave internal surface (Facies interna).
- Temporal bone — the sulcus runs along the mastoid process (Processus mastoideus), which continues into the petrous part (Pars petrosa).
- Occipital bone (Os occipitale) — the sulcus lies on the intracranial surface of the lateral parts (Partes laterales).
Topography on the parietal bone
On the internal surface (Facies interna) of the parietal bone, the following are identified:
- Sigmoid sulcus (Sulcus sinus sigmoidei).
- Sulcus for superior sagittal sinus (Sulcus sinus sagittalis superioris).
- Sulcus for middle meningeal artery (Sulcus arteriae meningeae mediae).
The parietal bone itself has four borders (sagittal, frontal, occipital, squamous) and four angles (frontal, occipital, sphenoidal, mastoid).
Topography on the temporal bone and communication with the external surface
On the temporal bone, the sigmoid sulcus is located on the mastoid process (Processus mastoideus). This process is prominent, directed posteriorly and laterally, and bounded by the occipital border (Margo occipitalis).
In this area, there is:
- Mastoid foramen (Foramen mastoideum) — through it, the sigmoid sulcus communicates with the external surface of the cranium.
The mastoid process also features the mastoid notch (Incisura mastoidea) and the occipital artery sulcus (Sulcus arteriae occipitalis).
Topography on the occipital bone
The sulcus is located on the intracranial surface of the lateral parts (Partes laterales) of the occipital bone.
On this surface, the following are identified:
- Jugular tubercle (Tuberculum jugulare).
- Hypoglossal canal (Canalis nervi hypoglossi) — located within the substance of the bone.
Jugular notch (Incisura jugularis) is located on the outer margin of the lateral part. Together with the petrous part of the temporal bone, it forms the jugular foramen (Foramen jugulare). Posteriorly, the notch continues into the jugular process (Processus jugularis), and anterior to it lies the intrajugular process (Processus intrajugularis), which separates the veins and nerves in the region of the foramen.
The lateral parts of the occipital bone bear the occipital condyle (Condylus occipitalis). Posterior to the condyle, a condylar fossa (Fossa condylaris) may be present, at the depth of which the condylar canal (Canalis condylaris) sometimes opens, serving as an emissary vein passageway.
Class and exam questions
On which surface of the parietal bone is the sigmoid sulcus located?
It is located on the inner, concave surface of the parietal bone (Facies interna), adjacent to the sulci for the superior sagittal sinus and the middle meningeal artery.
Through which foramen does the sulcus communicate with the external surface of the cranium?
The sigmoid sulcus communicates with the external surface of the cranium via the mastoid foramen (Foramen mastoideum), located on the mastoid process of the temporal bone.
What structures are identified on the intracranial surface of the lateral parts of the occipital bone?
The jugular tubercle (Tuberculum jugulare) and the hypoglossal canal (Canalis nervi hypoglossi), located within the substance of the bone, are identified.
What else to study on this topic
- Mastoid process of temporal bone (Processus mastoideus)
- Lateral parts of occipital bone (Partes laterales)
- Internal surface of parietal bone (Facies interna)
- Mastoid foramen (Foramen mastoideum)
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