Some specific anatomical features of the atlas and axis: dens, epitransverse process and articular facets.

Metrical and morphological findings, based on 107 human vertebral columns, related to the variations of the dens are given, and differences in the depth of the superior articular facets of the atlas and specific pertinent details related to the os odontoideum and epitransverse process are also provided and their possible clinical relevance indicated. Findings reveal considerable variation in the height of the dens (11 to 18 mm), but remarkably little in its anteroposterior and transverse diameters at the root. The use of the term "hypoplasia" with reference to the dens is discussed, and a need for more rigid criterian in the use of this term stressed. It is also suggested that there may be sufficient radiological evidence in a lateral radiography to lead one to suspect the presence of an os odontoideum or a separate dens caused by trauma in the distant past.