FIG. 2.

Posterior transformation of axial vertebrae in Btg2^−/− mice. (a to e) Axial skeletons and vertebrosternal ribs (insets) of wild-type (a) and Btg2^−/− (b to e) newborn pups. In wild-type mice, the thoracic, lumbar, and sacral vertebrae begin at V8, V21, and V27, respectively (a). In Btg2^−/− mice, the first rib (r1) is attached to V7 instead of V8 (b and c) and is joined to the second rib ventrally at the rostral end of the first sternebra (b, inset). The asterisks indicate the ribs attached in V20, which are either absent (b) or in the form of minute rudiments (d and e). The sacral vertebrae begin at V26 instead of V27 (b).