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Cervical vertebra 1 - atlas
Other Terms: Atlas (CI), C1 vertebra, First cervical vertebra, Atlas [C I]
The atlas is different from all other cervical vertebrae in its lack of a body. This bone has the shape of a ring with prominent lateral masses. These lateral masses are the thickest part of the bone. The major features of the lateral masses are the superior and inferior articular facets. Projecting laterally from each lateral mass is the transverse process. Perforating this projection of bone is the transverse foramen, a small hole that passes through the process. The two lateral masses are connected anteriorly and posteriorly by slender arches of bone, the anterior arch being shorter and thinner than the thicker, longer posterior arch.
The word cervical arises from the Latin term cervix meaning neck. This is an ancient term that has passed through the centuries literally unchanged. The word vertebra is an old Latin term that meant a joint or something to be turned. It arises from the Latin verto meaning to turn. In A.D. 30 Celsus used the word to designate any joint. It was only in later years that the bone arrived at its present meaning. The word atlas, referring to the first cervical vertebra, arises from the Greek God of the same name. Recall that Atlas was condemned by the great Zeus to bear the pillars of the universe on his shoulders. The bone bears our universe, the head, on its superior facets.
The atlas articulates with two bones: the occipital and the second cervical vertebra or axis. Its large, oval superior articular facets form a concave surface for the reception of the occipital condyles. On the inferior surface of the lateral masses, the inferior articular facets form flat surfaces for articulation with the superior articular facets of the axis.
The atlas ossifies from three centers. The first centers appear in the lateral masses during the seventh fetal week. These centers of ossification progress dorsomedially forming the posterior arch. At birth the central portion of the posterior arch is still cartilaginous. This eventually ossifies through the medial progression from the lateral masses, or sometimes from a separate center that appears in early postnatal life. A third center appears in the anterior arch around the first year. This center ossifies in a medial to lateral direction joining the lateral masses between the sixth and eighth year.
Atlas [C I]