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ATLAS (C1) ANATOMY

Author: Dr. Bogdan Leahu
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Atlas C1 vertebra anatomy 360-degree interactive viewer showing ring-like structure, lateral masses, anterior arch, and posterior arch
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TABLE OF CONTENTS

GENERAL CHARACTERISTICS

  • The first cervical vertebra, known as the atlas, supports the head
  • Unique structure — lacks both a vertebral body and a spinous process
  • Ring-like structure composed of:
    • Anterior arch
    • Posterior arch
    • Two lateral masses

LATERAL MASS

Atlas lateral mass 360-degree viewer showing superior and inferior articular surfaces with weight-bearing structures
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  • Comprises about one-fifth of the atlas' ring
  • Supports the weight of the head

Superior Articular Surface

  • Large, oval, concave facets converging anteriorly and diverging posteriorly
  • Oriented upwards, medially, and slightly backwards for articulation with occipital condyles

Inferior Articular Surface

  • Nearly circular, flat or slightly convex
  • Oriented downwards and medially
  • Forms joints with the axis' (C2) superior facets

Transverse Ligament Tubercle

  • Small prominence below the medial margin of the superior articular facet
  • Serves as an attachment point for the transverse ligament of the atlas

ANTERIOR ARCH

Atlas arches 360-degree viewer showing anterior arch with facet for dens and posterior arch with vertebral artery groove
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  • Forms about one-fifth of the atlas' ring
  • Front is convex with a smooth, oval or circular facet for articulation with the dens

Facet for Dens

  • Located on the concave posterior surface of the anterior arch
  • Ensures stability and movement by articulating with the dens of the axis

Anterior Tubercle

  • Central feature of the anterior arch
  • Attachment site for the Longus colli muscles

POSTERIOR ARCH (ARCUS POSTERIOR ATLANTIS)

  • Forms a large portion of the atlas' ring

Posterior Tubercle

  • Small bump at the center of the posterior arch
  • Represents a rudimentary spinous process
  • Serves as a muscle attachment site

Groove for Vertebral Artery (Sulcus Arteriae Vertebralis)

  • Pathway accommodating the vertebral artery
  • Located as it ascends through the transverse process

BIBLIOGRAPHY

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

QUICK FACTS: ATLAS (C1)

Key questions answered about this anatomy topic

Q: What makes the atlas (C1) unique among cervical vertebrae?

Answer: It lacks both a vertebral body and a spinous process. The atlas is unique in lacking both a vertebral body and a spinous process. Instead, it has a ring-like structure composed of anterior and posterior arches with two lateral masses.

Q: What percentage of the atlas' ring does each lateral mass comprise?

Answer: One-fifth. Each lateral mass comprises about one-fifth of the atlas' ring. The lateral masses are the weight-bearing portions that support the head.

Q: How are the superior articular surfaces of the atlas oriented?

Answer: Upwards, medially, and slightly backwards. The superior articular surfaces are large, oval, concave facets that are oriented upwards, medially, and slightly backwards for articulation with the occipital condyles.

Q: What is the shape of the inferior articular surface of the atlas?

Answer: Nearly circular, flat or slightly convex. The inferior articular surface is nearly circular and flat or slightly convex. It is oriented downwards and medially, forming joints with the axis' superior facets.

Q: What attaches to the transverse ligament tubercle?

Answer: The transverse ligament of the atlas. The transverse ligament tubercle is a small prominence below the medial margin of the superior articular facet that serves as an attachment point for the transverse ligament of the atlas.

Want to test yourself? Try the interactive quiz above!

⋮⋮ Atlas (C1) Quiz
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