The proatlas

Abstract

The proatlas is a rare, vestigial bone formation in humans, where it forms the occipital bone and the dorsal part of the foramen magnum after fusing with the upper three occipital sclerotomes. As a result, it is not generally observed as a separate structure. However, there are instances in which proatlantal remnants have been noted in man. On occasion, additional vertebra will appear in front of the atlas, thus the term “proatlas.”