Probe:	Spp1 probe
Probe preparation:	Antisense labelled with digoxigenin RNA
Visualized with:	Alkaline phosphatase

Structure	Level	Pattern	Image	Note
TS21: tibia-fibula pre-cartilage condensation	Absent		1C	Expression not detected at this stage.

Structure	Cell Type	Level	Pattern	Image	Note
TS22: bone		Present	Regionally restricted	2E	Expression in osteogenic cells of bone collar.
TS22: tibia cartilage condensation	chondrocyte	Present	Regionally restricted	2E	Expression in chondrocytes of central part of hypertrophic cell zone corresponding to lower hypertrophic cell zone.

Structure	Level	Pattern	Image	Note
TS23: tibia epiphysis	Present	Regionally restricted	3C	Expression on osteogenic cells of bone collar.
TS23: epiphyseal plate hypertrophic zone	Present	Regionally restricted	3C	Expression more extensive in lower hypertrophic cell zone.

Structure	Level	Pattern	Image	Note
TS22: mandible	Present	Graded	4C	Expression in osterogenic cells of bone tissue.
TS22: mandible condylar condensation	Absent		4C	No expression in cells with condylar anlage.

Structure	Cell Type	Level	Pattern	Image	Note
TS23: mandible		Present	Regionally restricted	5C	Expression in osteogenic cells of bone collar.
TS23: mandible condylar process	chondrocyte	Present		5C	Expression in newly formed chondrocytes.

Structure	Cell Type	Level	Pattern	Image	Note
TS24: mandible		Present	Regionally restricted	6C	Expression in osterogenic zone of bone collar.
TS24: mandible condylar process	chondrocyte	Strong	Regionally restricted	6C	Intense expression in chondrocytes of lower hypertrophic cell zone. Weak expression in upper hypertrophic cell zone.