[Development of the curvature of the cervical spine in utero. Attempted interpretation]

It is conventional saying that the fetal rachis shows only one ventral concavity. An echographic study allowed to observe in utero the rachis of more than a hundred live fetuses. The radius of this curvature gradually increases according to the development, revealed by the disappearance of the cervical curvature under the influence of the weight of the head and the uterine constraints. The sagittal curvatures of the vertebral column explains mans adaptability to the erected position. The authors think that the conventional conception, in which ontogenetic development is comparable with phylogenetic development, needs to be reconsidered: the cervical curvature is a prime curvature setting the evolutionist question about the origins of the rachidian curvatures.