General structure
Anatomifically, the occipital bone consists of four main parts that surround the foramen magnum (foramen magnum) like a ring:
- Basilar (anterior) part (pars basilaris) — lies anterior to the foramen.
- Lateral parts (partes laterales) — paired structures on the sides.
- Occipital squama (squama occipitalis) — the largest, dorsal part of the bone.
Basilar part (Pars basilaris)
This structure is directed forward and fuses with the sphenoid bone. Two surfaces are distinguished on it:
- Intracranial (superior) surface. This is the site of the clivus (clivus), which is adjacent to the ventral surface of the brainstem. The sulcus for the inferior petrosal sinus (sulcus sinus petrosi inferioris) runs along the sides of the clivus and continues onto the petrous part of the temporal bones.
- External (inferior) surface. Along the midline lies the pharyngeal tubercle (tuberculum pharyngeum), an important attachment site for the pharyngeal raphe/fibrous layer of the pharynx.
Lateral parts (Partes laterales)
They bear articular surfaces for connection with the spine and contain important canals.
- External surface: features the occipital condyle (condylus occipitalis), which participates in the formation of the atlanto-occipital joint. Posterior to it, the condylar fossa (fossa condylaris) may be located, at the bottom of which the inconstant condylar canal (canalis condylaris) sometimes opens for an emissary vein.
- Intracranial surface: laterally, the sulcus for the sigmoid sinus (sulcus sinus sigmoidei) is visible. Closer to the foramen magnum, the jugular tubercle (tuberculum jugulare) projects, and the hypoglossal canal (canalis nervi hypoglossi) runs through the bone underneath it.
- External border: contains the jugular notch (incisura jugularis). Together with the temporal bone, it forms the jugular foramen. Posteriorly, the notch is bounded by the jugular process (processus jugularis), and anteriorly by the intrajugular process (processus intrajugularis). Sometimes an accessory paramastoid process (processus paramastoideus) can be found on the external surface.
Occipital squama (Squama occipitalis)
The most massive part of the bone, shaped like a broad plate. Its superior border is called the lambdoid border (margo lambdoideus), and the lateral border is the mastoid border (margo mastoideus). Accessory interparietal bones (ossa interparietalia) are sometimes found along the suture line.
External surface (facies externa): In the center, the external occipital protuberance (protuberantia occipitalis externa) projects, from which the external occipital crest descends. Nuchal lines (muscle attachment sites) diverge to the sides from the protuberance and crest:
- Highest nuchal line (linea nuchalis suprema) — inconstant.
- Superior nuchal line (linea nuchalis superior).
- Inferior nuchal line (linea nuchalis inferior).
Below these lines lies the planum occipitale (planum occipitale).
Internal surface (facies interna): The relief of the cerebral surface is determined by the impressions of the brain and venous sinuses. In the center is the cruciform eminence (eminentia cruciformis) with the internal occipital protuberance in the middle. Sulci diverge from it:
- Superiorly — sulcus for the superior sagittal sinus.
- Laterally — sulci for the transverse sinus.
- Inferiorly runs the internal occipital crest, often transitioning into the sulcus for the occipital sinus (and near the edge of the foramen magnum — into the sulcus for the marginal sinus).
The cruciform eminence divides the squama into four fossae: two superior cerebral fossae (fossae cerebrales) and two inferior cerebellar fossae (fossae cerebellares).
Briefly: answers to topical questions
Which muscles attach to the nuchal lines of the occipital bone?
On the external surface of the occipital squama, nuchal lines diverge from the external occipital protuberance. Below these line zones lies the planum occipitale, which serves as the attachment area for the muscles of the back of the head.
Which bones participate in the formation of the jugular foramen?
The jugular notch of the occipital bone, together with the petrous part of the temporal bone, directly participates in the formation of the jugular foramen.
Which cranial nerves pass through the jugular foramen?
The glossopharyngeal, vagus, and accessory nerves exit the cranial cavity through the jugular foramen.
The cruciform eminence divides the internal surface of the squama into 4 fossae: two superior for the cerebral hemispheres Brain (fossae cerebrales), two inferior for the Cerebellum (fossae cerebellares). How to remember: the cerebrum is anatomically always located above the cerebellum!
Class and exam questions
What is the clivus and where is it located?
The clivus is a smooth surface on the internal side of the basilar part of the occipital bone (fused with the sphenoid). The pons and medulla oblongata rest upon it.
What is the difference between the condylar canal and the hypoglossal canal?
The hypoglossal canal (canalis nervi hypoglossi) pierces the base of the condyle and transmits the XII cranial nerve. The condylar canal (canalis condylaris) is located posterior to the condyle, is inconstant, and serves for the passage of an emissary vein.
How is the jugular foramen formed?
It is formed by the junction of the jugular notch of the occipital bone (incisura jugularis) with the corresponding notch on the petrous part of the temporal bone.
What else to study on this topic
- Topography of the jugular foramen: vessels and nerves passing through it
- Diagram of the venous sinus pathway on the internal surface of the occipital squama
- Neck and back muscles attached to the nuchal lines
- Biomechanics of the atlanto-occipital joint
- Developmental anomalies: interparietal bone (inca bone) and variations in process structure
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