Comparison of the approximate limits of expression in the snake and a “model” vertebrate skeleton shows that an ancestral pattern of global collinear Hox gene expression along the trunk is thus largely conserved (Fig. 3).
Contrary to expectations, therefore, we find that the somitic mesoderm, which will give rise to the dorsal homogeneous rib-bearing part of the skeleton, is regionalized by Hox genes which are known to possess vertebra-modifying or even ribsuppressing activity in the mouse.
Despite this regionalization, the dorsal skeleton however shows no or very little regionalization of vertebral anatomy.