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3D OSTEOLOGY
3D NEUROCRANIUM

OCCIPITAL BONE ANATOMY

Author: Dr. Bogdan Leahu
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Occipital bone anatomy 360-degree interactive viewer showing foramen magnum, basilar part, lateral parts, squamous part, and occipital condyles
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GENERAL CHARACTERISTICS

  • Trapezoidal cranial bone positioned at the posteroinferior aspect of the skull
  • Forms the posterior and inferior walls of the cranial cavity
  • Articulates with parietal, temporal, and sphenoid bones

STRUCTURAL COMPONENTS

  • Composed of four parts surrounding the foramen magnum
    • Squamous part
    • Basilar part
    • Two lateral parts

FORAMEN MAGNUM

  • Large central aperture of the occipital bone
  • Transmits the brainstem at the junction of medulla oblongata and spinal cord
  • Serves as a conduit for nerves and vessels passing between cranial cavity and vertebral canal

BASILAR PART

Basilar part of occipital bone 360-degree viewer showing anterior position relative to foramen magnum and fusion with sphenoid bone
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Basilar Part of the Occipital Bone, Preview from the app. Download 3D OSTEOLOGY for full 3D control—multiple views, x-ray mode, and unlimited zoom.

  • Located anterior to the foramen magnum
  • Fuses with the sphenoid bone anteriorly

LATERAL PARTS

Lateral parts of occipital bone 360-degree viewer showing occipital condyles, hypoglossal canal, jugular notch, and jugular process
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Lateral Parts of the Occipital Bone, Preview from the app. Download 3D OSTEOLOGY for full 3D control—multiple views, x-ray mode, and unlimited zoom.

  • Positioned on both sides of the foramen magnum
  • Occipital Condyles — oval prominences on inferior surface; articulate with atlas (C1) forming the atlanto-occipital joint for head nodding
  • Condylar Fossa — depression posterior to each condyle; may contain opening of the condylar canal (transmits emissary veins)
  • Hypoglossal Canal — located superior to foramen magnum, courses anterolaterally; transmits hypoglossal nerve (CN XII)
  • Jugular Tubercle — oval elevation on superior surface; contributes to jugular foramen formation
  • Jugular Notch — forms part of jugular foramen; transmits internal jugular vein and cranial nerves
  • Jugular Process — extends laterally; provides attachment for muscles and ligaments
  • Intrajugular Process — bony projection that may divide jugular notch; can form septum within jugular foramen

SQUAMOUS PART

  • Largest and most posterior portion of the occipital bone
  • Located posterior to the foramen magnum
  • Provides attachment sites for nuchal muscles and ligaments

External Surface

External surface of squamous part 360-degree viewer showing external occipital protuberance, nuchal lines, and muscular attachment sites
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External Surface of the Squamous Part, Preview from the app. Download 3D OSTEOLOGY for full 3D control—multiple views, x-ray mode, and unlimited zoom.

  • External Occipital Protuberance — midline prominence palpable through the scalp
  • External Occipital Crest (Median Nuchal Line) — descends from protuberance toward foramen magnum; attachment for nuchal ligament
  • Nuchal Lines:
    • Supreme Nuchal Line — faint ridge above external occipital protuberance
    • Superior Nuchal Line — horizontal ridge at level of protuberance; muscle attachment
    • Inferior Nuchal Line — horizontal ridge below superior line; additional muscle attachments
  • Occipital Plane — region above supreme nuchal line; contributes to posterior cranial curvature

Internal Surface

Internal surface of squamous part 360-degree viewer showing cruciform eminence, cerebral and cerebellar fossae, and venous sinus grooves
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Internal Surface of the Squamous Part, Preview from the app. Download 3D OSTEOLOGY for full 3D control—multiple views, x-ray mode, and unlimited zoom.

  • Cruciform (Cruciate) Eminence — cross-shaped elevation dividing surface into four fossae; Internal Occipital Protuberance at center
  • Internal Occipital Crest — descends from protuberance; forms inferior limb of cruciform eminence
  • Venous Sinus Grooves:
    • Groove for Transverse Sinuses — horizontal grooves accommodating transverse dural venous sinuses
    • Groove for Occipital Sinus — follows internal occipital crest; houses occipital sinus
    • Groove for Marginal Sinus — traces inferior margin of foramen magnum
  • Cranial Fossae:
    • Cerebral Fossae — superior fossae accommodating occipital lobes of cerebrum
    • Cerebellar Fossae — inferior fossae housing cerebellar hemispheres
    • Vermian Fossa — small depression accommodating cerebellar vermis

BIBLIOGRAPHY

1. Henry G, Warren HL. Osteology. In: Anatomy of the Human Body. 20th ed. Philadelphia: Lea & Febiger; 1918. p. 129–97.

QUICK FACTS: OCCIPITAL BONE

Key questions answered about this anatomy topic

Q: What is the occipital bone?

Answer: An unpaired bone forming the back and base of the skull. The occipital bone is an unpaired cranial bone that forms the posterior and inferior portions of the skull. It contains the foramen magnum, the large opening through which the brainstem connects with the spinal cord.

Q: Where is the occipital bone located?

Answer: At the back and base of the skull. The occipital bone is located at the posteroinferior aspect of the skull. It forms the back of the head and part of the skull base, surrounding the foramen magnum.

Q: What is the function of the occipital bone?

Answer: To protect the brain and enable head movement on the spine. The occipital bone protects the posterior brain (cerebellum and occipital lobes) and enables head movement by articulating with the atlas (C1) vertebra at the atlanto-occipital joint, allowing nodding motions.

Q: How many occipital bones are there in the skull?

Answer: One (unpaired). There is only one occipital bone in the skull. It is an unpaired bone located at the back and base of the skull, forming the posterior cranial fossa.

Q: What is the foramen magnum?

Answer: The large opening in the occipital bone for the brainstem and spinal cord. The foramen magnum is the large oval opening in the occipital bone through which the brainstem (medulla oblongata) transitions to the spinal cord. It also transmits the vertebral arteries, spinal accessory nerves, and meninges.

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