Table 1.

Spatial localization of gene expression in HH33 and HH36 control duck.

Structure	Tissue type		FGF signaling pathway					TGFβ signaling pathway
			Fgf4	Fgf8	Fgfr2	Fgfr3	Pea3	Tgfβ2	Tgfβ3	Tgfβr2	Smad3
Control Duck at HH33
Meckel’s Cartilage	Primary Cartilage	Perichondrium1			X		X
		Cartilage2	X	X	X	X	X		X	X	X
Coronoid Process	Secondary Cartilage	Condensation	X	X	X		X	X	X	X	X
Surangular	Bone	Condensation3	X	X	X	X	X
Mandibular Adductor	Muscle4		X	X			X	X	X	X	X
Muscle Insertion	Tendon		X	X			X	X	X	X	X
Structure	Tissue type		FGF signaling pathway					TGFβ signaling pathway
			Fgf4	Fgf8	Fgfr2	Fgfr3	Pea3	Tgfβ2	Tgfβ3	Tgfβr2	Smad3
Control Duck at HH36
Meckel’s Cartilage	Primary Cartilage	Perichondrium	X		X	X	X	X	X		X
		Cartilage	X	X	X	X	X	X	X		X
Coronoid Process	Secondary Cartilage	Perichondrium		X				X	X		X
		Cartilage5	X	X	X	X	X	X	X	X	X
Surangular	Bone	Periosteum6	X	X	X	X	X	X	X		X
		Bone	X	X	X	X	X	X	X	X	X
Mandibular Adductor	Muscle7		X	X	X	X	X	X	X		X
Muscle Insertion	Tendon		X	X	X	X	X	X	X		X

¹Strong Fgfr2 expression throughout the perichondrium with isolated cells expressing Pea3.

²Strong Fgfr3 expression throughout with isolated cells expressing Fgf8 and Pea3.

³Strong Fgfr2 expression throughout the surangular condensation with isolated Pea3 expressing cells.

⁴Fgf4 and Pea3 expression appear strongest near muscle tips while Tgfβ2 is strongly expressed throughout the muscle.

⁵Strong Fgfr2 expression throughout while Fgfr3 expression is spatially restricted to the center.

⁶Fgfr2 and Fgfr3 are expressed throughout bone, but periosteal expression is quite strong.

⁷Smad3 expression strongest near muscle insertions.