Fissures in the anterior arch of the atlas diagnosed by careful study of the lateral radiographs.

Fissures in the anterior arch of the atlas are rare. The defect can properly be diagnosed on axial radiographs and can be suspected in studying carefully the lateral x-ray. The developmental cause of the split anterior arch and its clinical significance are discussed. A median cleft, analogous to a fissure in the anterior arch of the atlas, may also occur in the proatlas, as shown in one case.