Anatomy of the Atlas (First Cervical Vertebra)

General Description

• The atlas is the first cervical vertebra.
• Unique shape, unlike typical cervical vertebrae.
• Notable for lacking a body.
• Comprises two lateral masses connected by dorsal and ventral arches forming the vertebral foramen.

Key Structures

Cardinal View

• Lateral Masses: Two significant lateral masses.
• Dorsal Arch: Links the lateral masses dorsally.
• Ventral Arch: Connects the lateral masses ventrally.

Dorsal View

• Dorsal Tubercle: Prominent structure on the dorsal arch.
• Ventral Tubercle: Located on the ventral arch.
• Wings of the Atlas: Modified transverse processes.
• Atlantic Fossa: Notable depressions on the wings.

Cranial View

• Articular Surface: For articulation with occipital condyles.
• Notches: Ventral and dorsal notches separating the cranial articular surfaces.

Caudal View

• Caudal Articular Processes: For articulation with the axis.
• Fovea Dentis: Articulates with the dens of the axis.
• Ligamentum Dentis: Rough areas for ligament attachment.

Foramina

• Lateral Vertebral Foramen: Opens into the vertebral canal.
• Alar Foramen: Opens through the wing of the atlas into the atlantic fossa.
• Transverse Foramen: Located at the base of the wing.

Comparative Anatomy

Horse

• Dorsal Tubercle: Well-developed.
• Foramina: Three types (lateral vertebral, alar, transverse).
• Wings of the Atlas: Ventral and caudoventrally directed.

Camel

• Foramina: Separated lateral vertebral and alar foramina.
• Dorsal Tubercle: Less distinct.

Ox and Sheep

• Dorsal Tubercle: Prominent and rounded.
• Foramina: Connected lateral vertebral and alar foramina; absent transverse foramen.
• Wings of the Atlas: Thicker and more transverse.

Dog and Cat

• Foramina: Present transverse and lateral vertebral foramen; alar notch instead of alar foramen.
• Wings of the Atlas: Flat, horizontal, and butterfly-shaped.
• Ventral Arch: Narrow in dogs.

Ventral Surface

• Ventral Tubercle: Well-developed in horses and oxen; absent in camels.
• Ventral Arch: Narrower in dogs compared to other animals.
• Atlantic Fossa: Deep in horses and oxen; less so in camels and not present in carnivores.

Additional Notes

• Smooth Articular Surface: Facilitates movement with dens of the axis.
• Depressions: For ligamentum dentis attachment.