Figure 2.

The anterior‐most vertebral elements in meox1 ^cho mutants have fusions within and across vertebrae. (A–E) Maximum intensity Z‐projections of Weberian centra (respectively, dorsal, ventral and lateral views) and neural arches (respectively, medioanterior and lateral views) isolated from siblings reveal that centra and neural arches are discrete and conterminous bony elements within the Weberian apparatus. Articular surfaces are apparent (asterisks). (F–H) In meox1 ^cho homozygotes, neural arches are fused to centra (dotted lines), excepting where a centrum has fused to its arches and an arch of its neighbour (G, arrows). Where fusion incorporated two centra into a single bony element, the intervertebral gap was discernible (arrowheads). (F–H) Lateral views, where anterior is left. na, neural arch; ns, neural spine. Scale bars: 500 μm.