CorpusHuman Anatomy
SkeletalBone

Occipital bone

Os occipitale

The trapezoid-shaped bone forming the back and much of the base of the cranium. It surrounds the foramen magnum and articulates with the atlas through its occipital condyles.

Show on body map Skull — Lateral View

Overview

The occipital bone consists of four parts arranged around the foramen magnum: the squamous part behind, two lateral (condylar) parts, and the basilar part in front, which slopes up to fuse with the sphenoid body forming the clivus (spheno-occipital synchondrosis fuses ≈13–18 years).

Externally, the external occipital protuberance (inion) and the superior nuchal lines mark the attachment of trapezius and the ligamentum nuchae; the inferior nuchal lines lie below. On the lateral parts sit the occipital condyles, which articulate with the superior facets of the atlas (atlanto-occipital joints). The hypoglossal canal passes above each condyle; the condylar canal (emissary vein) lies behind it; the jugular notch contributes to the jugular foramen. Internally, the cruciform eminence marks the internal occipital protuberance and the grooves for the transverse sinuses, the confluence of sinuses and the attachment of the falx cerebelli and tentorium cerebelli; the cerebellar fossae lodge the cerebellar hemispheres.

Location

Posterior and inferior part of the cranium.

Parts & subdivisions

  1. Foramen magnum
    Largest skull foramen: medulla oblongata/spinal cord junction and meninges, vertebral arteries, anterior and posterior spinal arteries, spinal roots of the accessory nerve (CN XI), tectorial membrane and alar/apical ligaments.
  2. Occipital condyles
    Convex, kidney-shaped surfaces articulating with the atlas.
  3. Hypoglossal canal
    Above each condyle; transmits the hypoglossal nerve (CN XII).
  4. Jugular foramen (with temporal bone)
    Glossopharyngeal (IX), vagus (X) and accessory (XI) nerves, internal jugular vein (sigmoid sinus) and inferior petrosal sinus.
  5. Basilar part (clivus)
    Supports the pons and medulla; joins the sphenoid at the spheno-occipital synchondrosis.
  6. External occipital protuberance (inion)
    Palpable midline bump; attachment of ligamentum nuchae and trapezius.
  7. Superior and inferior nuchal lines
    Attachments for trapezius, sternocleidomastoid, splenius capitis, semispinalis and the suboccipital muscles.
  8. Internal occipital protuberance
    Overlies the confluence of the sinuses.

Anatomy

Articulations

Parietals (lambdoid suture), temporals (occipitomastoid suture), sphenoid (spheno-occipital synchondrosis), atlas (atlanto-occipital joints).

Ossification

Mixed: the squama above the highest nuchal line (interparietal part) is intramembranous; the rest (supra-occipital, two exoccipitals, basi-occipital) is endochondral. The parts fuse by ≈6 years.

Function

  • Protects the occipital lobes, cerebellum and brainstem
  • Forms the posterior cranial fossa
  • Transmits the medulla and vessels through the foramen magnum
  • Articulates with the vertebral column (nodding movements)
  • Attachment for nuchal ligament and posterior neck muscles

Clinical significance

Chiari malformation

Herniation of the cerebellar tonsils through the foramen magnum (type I), associated with syringomyelia; presents with occipital headache worsened by coughing.

Tonsillar (coning) herniation

Raised intracranial pressure forces the cerebellar tonsils into the foramen magnum, compressing the medulla — respiratory arrest.

Compiled from standard anatomy and physiology references — see the Skeletal System sources. For education only; not medical advice.