Anatomical variants of the cervical vertebrae and the first thoracic vertebra in man.

Anatomical variants of the cervical part of the human spine were investigated. Morphological variants were studied on 100 cervical vertebrae (37 female and 63 male). The greatest variability was demonstrated by the first cervical vertebra or atlas. The presence of some accessory bony arches embracing the vertebral artery was observed, namely the posterior bridge restraining the arcuate foramen (13.8%) and the lateral bridge restraining the transversovertical foramen (2%). Split posterior (3%) or anterior (1%) arches of the atlas were also encountered in this material. The superior articular face of the atlas divided into two parts was found in 47.8%. Variants of the remaining cervical vertebrae were limited only to the presence of a division of the transverse process foramina or their incomplete closure. Some of these anatomical variants may be a cause of certain clinical symptoms which have previously been described in the literature.