Fig. 7. Expression of Bapx1 in the chick jaw joint. (A) Section stained with Haematoxylin/Eosin. (C,E,H) Sections stained with Alcian Blue and chlorantine Fast Red. (B,D,F,I) ³⁵S radioactive in situ hybridisation for Bapx1. (G) ³⁵S radioactive in situ hybridisation for Runx2. (A,B,E-I) Frontal sections. (C,D) Sagittal sections. (A,B) E7. (C-G) E9. (H,I) E12. (A,B) Expression of Bapx1 in the quadrate and articular cartilages of the jaw and in between in the developing jaw joint (arrow). (C,D) By E9, expression of Bapx1 is downregulated in the cartilages of the jaw but remains high in the jaw joint itself (arrow). (E) Frontal view showing the developing membranous bones associated with the articular. The presumptive prearticular is marked by an asterisk. (F) Expression of Bapx1 coinciding with the region of the presumptive prearticular and around the angular and surangular bones surrounding the jaw joint. (G) Expression of the bone marker Runx2 within the developing membranous bones (angular, surangular and prearticular). (H,I) Expression of Bapx1 around the membranous bones surrounding the articular at E12 but not within these bones. A, articular; Q, quadrate; An, angular; S, surangular, P, prearticular.