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The Occipital Bone

Overview

The occipital bone is an unpaired bone which covers the back of the head (occiput). It makes up a large portion of the basilar part of the neurocranium and houses the cerebellum. It is the only cranial bone to articulate with the cervical spine.

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Structures seen on the posterior and lateral views of the skull.

Anatomy

Foramen Magnum

The bone is convex externally and concave internally. It is divided into four parts: the basilar part, two condylar parts and the squamous part. All four are arranged around a large opening, the foramen magnum. Structures that pass through this foramen magnum include:

Foramen magnum - cranial view

Foramen magnum - cranial view

Basilar Part

The basilar part sits anterior to the foramen magnum and adjacent to the petrous part of the temporal bone. Anteriorly it fuses with the sphenoid bone to form the clivus during adolescence (tribasilar bone). Both the superior pharyngeal constrictor muscle and the pharyngeal raphe insert onto the pharyngeal tubercle found on the inferior surface of the basilar part.

Basilar part of occipital bone - medial view

Basilar part of occipital bone - medial view

Condylar Parts

The condylar parts are located lateral to the foramen magnum. They comprise two kidney-shaped prominences (occipital condyles) that articulate with the first cervical vertebra (atlanto-occipital joint). Posterior to the them are the condylar canals where the condylar emissary veins pass through and connect the external vertebral venous plexuses with the sigmoid sinuses. The hypoglossal nerve exits through the hypoglossal canal which pierces through the condylar part of the occipital.

Condylar canal - caudal view

Condylar canal - caudal view

Squamous Part

The squamous part is the largest of all four. A palpable prominence known as the external occipital protuberance lies on the midline of the external surface which serves as an attachment for the trapezius muscle.

External occipital protuberance - dorsal view

External occipital protuberance - dorsal view

Furthermore the external surface features three curved lines referred to as nuchal lines:

  • The highest nuchal line extends laterally from the external occipital protuberance and is the site of origin of the epicranius muscle and epicranial aponeurosis.
  • The superior nuchal line runs slightly inferior. It provides origin to the trapezius, sternocleidomastoid and splenius capitis muscles.
  • The inferior nuchal line runs further inferiorly. The semispinal capitis muscle inserts above it.

Superior nuchal line - dorsal view

Superior nuchal line - dorsal view

The squamous part of the occipital bone is marked by grooves on its internal surface due to dural venous cranial sinuses: the superior sagittal sinus, the transverse sinuses and the sigmoid sinus. Superior to the groove for the transverse sinus is a depression that accommodates the occipital brain lobes (cerebral fossa) and the corresponding inferior depression houses the cerebellum (cerebellar fossa).

Borders

The occipital bone is bordered superiorly and laterally by the lambdoid suture which separates it from the parietal bones. It articulates with the mastoid process through the occipitomastoid suture. The petro-occipital suture joints the petrous part of the temporal bone with the occipital bone. The spheno-occipital suture between the sphenoid and occipital bones disappears as they fuse during adolescence.

Occipital bone - dorsal view

Occipital bone - dorsal view

Osseous Development

The basilar and condylar parts develop through endochondral ossification. Most of the squamous part undergoes endochondral ossification as well, except its superior part which develops through the intramembranous pathway. In newborns all four parts are separated by connective tissue. By the age of four the squamous and condylar parts will usually have ossified together whereas the basilar portion joins them at age six.

Summary

The occipital bone is an unpaired bone which covers the back of the head (occiput). It is divided into four parts arranged around the foramen magnum, as follows:

  • basilar part - sits anterior to the foramen magnum and adjacent to the petrous part of the temporal bone. There is also a pharyngeal tubercle on the inferionr surface of the basilar part.
  • condylar parts - are located lateral to the foramen magnum and comprise two occipital condyles. Posterior to them are the condylar canals, while the hypoglossal canal also pierces through the condylar part of the occipital bone.
  • squamous part - it contains a palpable prominence named the external occipital protuberance, together with three nuchal lines and grooves for the dural venous sinuses,

The occipital bone is bordered by the lamboid, occipitomastoid, and the petro-occipital sutures. In addition, it develops through both endochondral and intramembranous ossifications.

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Show references

References:

  • Neil S. Norton, Frank H. Netter: Netter’s Head and Neck Anatomy for Dentistry, 2nd edition, Elsevier Saunders, p.27, 30-31, 49-51.
  • Petr Suchomel, Ondřej Choutka: Reconstruction of upper cervical spine and craniovertebral junction, Springer (2011), p.71
  • A. Halim: Human Anatomy - Regional and Clinical for Dental Students, I.K. International Publishing (2008), p.11-15
  • Wolfgang Dauber: Pocket Atlas of Human Anatomy, 5th edition, Thieme (2007), p.26
  • Friedrich Anderhuber, Franz Pera, Johannes Streicher: Waldeyer Anatomie des Menschen, 19th edition, De Gruyter (2012), p.703, 705, 715

Author:

  • Dr. Alexandra Sieroslawska

Illustrators:

  • Foramen magnum - cranial view - Yousun Koh
  • Basilar part of occipital bone - medial view - Yousun Koh
  • Condylar canal - caudal view - Yousun Koh
  • External occipital protuberance - dorsal view - Yousun Koh
  • Superior nuchal line - dorsal view - Yousun Koh
  • Occipital bone - dorsal view - Yousun Koh
© Unless stated otherwise, all content, including illustrations are exclusive property of Kenhub GmbH, and are protected by German and international copyright laws. All rights reserved.

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