Fig. 6. Mineralization of the skull base. After the slight delay of ossification observed in the mutant at E16.5, sutures between exoccipital and basioccipital bones begin to close as early as E18.5. White arrows point to the basioccipital-exoccipital junction, where in the mutant precocious fusion takes place. Black arrows on the P14 mutant specimen indicate complete fusion of the basioccipital-exoccipital suture and contact at the basioccipital-basisphenoid suture; the vertical arrow indicates the abnormal position of the basisphenoid-presphenoid suture beneath the palate, due to shortening of the sphenoid area in the mutant. bo, basioccipital bone; pal, palate; bs, basisphenoid bone; eo, exoccipital bone; ps, pre-sphenoid so, supraoccipital bone.

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