axis

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axis The second cervical vertebra, which articulates with the atlas (the first cervical vertebra, which articulates with the skull). The articulation between the axis and atlas in reptiles, birds, and mammals permits side-to-side movement of the head. The body of the axis is elongated to form a peg (the odontoid process), which extends into the ring of the atlas and acts as a pivot on which the atlas (and skull) can turn.

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