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Calvaria

Contents

General Features

The word ‘Diploe’ is a general term used to describe the spongy or cancellous region of intervening bone between the hard outer cortical shell and the brittle inner shell (as with the skull). The term is usually used for bones of the skull, but can be used for other short bones. The Parietal foramina are not always present and are found in the posterosuperior region of the parietal bone and form the channel for the emissary vein to connect with the superior sagittal sinus. They sometimes communicate with the occipital vein. The Granular Foveolae can be described as pits found on the inner surface of the skull along the length of the superior sagittal sinus and mark the region where the arachnoid granulations lodge.

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Structures seen on the superior and inferior views of the calvaria.

Bones of the Calvaria

Frontal Bone

The frontal bone forms the anterior most part of the superior skull and overlies the frontal lobe. The frontal crest is a ridge in the anterior squamous portion of the frontal bone and is formed by the convergence of the two ridges of the superior sagittal sinus. The fold of dura that divides the two cerebral hemispheres (the falx cerebri) attaches at this point.

Frontal bone - cranial view

Frontal bone - cranial view

The bone forms synarthrosis joints with the adjacent sphenoid, zygomatic and parietal bones. The area where these four bones articulate is termed the anterior pterion which overlies the middle meningeal artery (a branch of the maxillary artery). In infancy the sphenoid fontanel lies here, allowing for the bones of the skull to move over eachother to enable passage of the head through the birth canal. The frontal bone contains the frontal sinus which protects the brain from direct skull trauma.

Occipital Bone

The occipital bone forms the posterior part of the skull and articulates with the parietal bones superiorly and forms the occipital condyles inferiorly. These condyles articulate with the lateral masses of the atlas. Atlas was the Greek titan who carried the skies, so the C1 vertebra has received an appropriately important name!

Occipital bone - cranial view

Occipital bone - cranial view

Parietal Bone

The parietal bone articulates with the frontal bones anteriorly and the occipital bones posteriorly. The bones are the largest bones of the skull and articulate in the midline via the sagittal suture. The parietal lobe underneath is involved in sensory perception. Early fusion of the sagittal suture gives rise to scaphocephaly. This bone is imprinted by meningeal arteries that lie within the substance of the dura mater.

Parietal bone - cranial view

Parietal bone - cranial view

Structures and Foramina within the Calvaria

The arterial grooves are indentations of the meningeal arteries on the inner surface of the skull. The middle meningeal artery enters the skull through the foramen spinosum located a few millimetres lateral and posterior to the foramen ovale. The artery supplies blood to the meninges along with the anterior and posterior meningeal arteries. The anterior is a branch of the anterior ethmoidal artery which enters the cranium through the canal of the same name. The posterior artery variably enters the skull through the jugular foramen, foramen magnum or hypoglossal canal.

Arterial grooves - caudal view

Arterial grooves - caudal view

The superior sagittal sinus runs in the attached margin of the falx cerebri and drains the lateral aspects of the anterior cerebral. It drains into the confluence of the sinuses (located deep to the posterior pterion). The sinus grooves the middle, inner surfaces of the frontal bone, both parietal bones in the sagittal plane and the cruciate eminence of the occipital bone.

Groove for superior sagittal sinus - caudal view

Groove for superior sagittal sinus - caudal view

Sutures

Sagittal Suture

The sagittal suture lies in the midline of the brain, extending from the coronal suture to the occipital bone posteriorly. The metopic suture is the anterior continuation of the sagittal suture and fuses at one year of age. Premature fusion causes trigonocephaly. The sutures of the skull are examples of synarthrosis joints, and are part of the group that includes gomphosis (teeth sockets) synchondrosis (a cartilaginous joint joined together by hyaline cartilage) and synostoses. The sagittal suture divides both parietal bones superiorly and lies in the mid sagittal plane. Both parietal bones fuse at around age 30, making it the last suture to fuse. This suture also overlies the superior sagittal sinus.

Sagittal suture - cranial view

Sagittal suture - cranial view

Coronal Suture

The coronal suture lies between the frontal bone and the two parietal bones, approximately one third along the superior skull. It fuses fully at around 25 years of age along with the lambdoid suture.

Coronal suture - cranial view

Coronal suture - cranial view

Lambdoid Suture

The lambdoid suture fuses at 25 years of age and lies between the parietal bones superiorly and the occipital bone inferiorly. It extends from the back of the skull to the posterior pterion. The posterior pterion forms at the joining of the occipital, parietal and temporal bone and was formerly the mastoid fontanel in infancy.

Lambdoid suture - cranial view

Lambdoid suture - cranial view

Squamous Suture

The squamous suture lies between the temporal bone inferiorly and the parietal bone superiorly. It joints anterior pterion to posterior pterion.

Squamous suture - lateral-left view

Squamous suture - lateral-left view

Summary

The bones forming the calvaria are the frontal, occipital and parietal bones. They join together, forming structures called sutures, each one having a specific name. They include the sagittal suture (parietal-parietal), coronal suture (frontal-parietal), lambdoid (parietal-occipital), and squamous (temporal-parietal).

The calvaria also contains some specific features and foramina. There are arterial grooves for the passage of the meningeal arteries, and a long groove for the superior sagittal sinus. In addition, on the calvaria you can find the granular foveolae, where the arachnoid granulations lodge.

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Show references

References:

  • Frank H.Netter MD: Atlas of Human Anatomy, 5th Edition, Elsevier Saunders, Chapter 1 Head and Neck, Skull: Lateral View, Page 9 to 11.
  • Chummy S.Sinnatamby: Last’s Anatomy Regional and Applied, 12th Edition, Churchill Livingstone Elsevier, Chapter 8 Osteology of the Skull and Hyoid bone, Page 503.
  • Richard L. Drake, A. Wayne Vogl, Adam. W.M. Mitchell: Gray’s Anatomy for Students, 2nd Edition, Churchill Livingstone Elsevier, Chapter 8 Head and Neck, Page 816 to 823.
  • Richard L. Drake, A. Wayne Vogl, Adam. W.M. Mitchell: Dorland’s Gray’s Pocket Atlas of Anatomy, Churchill Livingstone Elsevier , Chapter 8 Head and Neck, Page 369-371.

Author and Layout:

  • Shahab Shahid
  • Catarina Chaves

Illustrators:         

  • Frontal bone - cranial view -  Yousun Koh
  • Occipital bone - cranial view - Yousun Koh
  • Parietal bone - cranial view - Yousun Koh
  • Arterial grooves - caudal view - Yousun Koh
  • Groove for superior sagittal sinus - caudal view - Yousun Koh
  • Sagittal suture - cranial view - Yousun Koh
  • Coronal suture - cranial view - Yousun Koh
  • Lambdoid suture - cranial view - Yousun Koh
  • Squamous suture - lateral-left 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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