The human vertebral column at the end of the embryonic period proper. 1. The column as a whole.

The present investigation of the vertebral column at 8 post-ovulatory weeks, the first such study based on precise reconstructions, has revealed 33 or 34 cartilaginous vertebrae arranged in flexion and approximately 20--33 mm in total length. At the end of the embryonic period proper, a typical vertebra, such as TV6, consists of a centrum that is continuous with two neural processes. Pedicles, articular and transverse processes, but no spinous processes, are identifiable. The tips of the neural processes, which are formed by the laminae, are connected by fibrous tissue and resemble the condition of total rachischisis. The union of the laminae, the onset of ossification, and the appearance of articular cavities are characteristic of the early fetal period. The variations encountered within a single developmental stage were noted. They were mostly minor, e.g. the number of coccygeal elements and the extent of the dorsal growth of the neural processes.