[Fusion of the cervical vertebrae of mammals]

Morphogenesis of the cervical vertebrae has been investigated in Dipis sagitt. and in Rattus norvegicus. The main distinctive feature of the Dipis embryos at the mesenchymal stage is their very thin perichordal intervertebral rings. As a result, short cartilaginous vertebral bodies and thin intervertebral discs develop, cervical segments lengthen more slowly than those of the Rattus. Because of the small length of the Dipis cervical segments, the cartilaginous neural arches and the transverse processes of 2-6 vertebrae draw nearer and fuse. Owing to the insufficient development of the Dipis intervertebral discs and the nuclei pulposae, the normal formation of the vertebral epiphyses is disturbed, this results in fusion of the neighbouring osseous vertebral bodies.