Table 1 Expression domains of the genes in the head of crocodile, turtle, and snake embryos

Runx2

St.14/15: The domain dorsal to the oral cavity where the ventral part of the braincase and future palatine and pterygoid bones develop; a domain dorsolateral to the orbit where the future dorsal projection of the postorbital bone forms; the domain ventrolateral to the orbit where future jugal and postorbital bones form; the mesenchyme that later differentiates into the main body of the postorbital bone.

St.14/15: A population of cells medial to the precursor of the jaw adductor muscles; the mesenchyme localized at the domain dorsolateral and ventrolateral to the orbit; a thick layer of the mesenchymal cells that completely covers the brain and the precursor of jaw adductor muscle laterally.

St.26: The mesenchyme occupying the space medial to the quadrate cartilage precursor; the mesenchyme ventral to the orbit; a layer of mesenchymal cells surrounding the brain laterally.

St.17: The cell populations localized to the area where the future dermatocranium differentiates (palatine, parietal, postorbital, pterygoid, quadratojugal bones).

St.17: A thick layer of mesenchymal cells surrounding the braincase and jaw adductor muscle laterally; the mesenchyme associated with the quadrate cartilage and the ventral part of the braincase.

St.29: The precursors of palatine and pterygoid bones; the mesenchyme accompanying jaw cartilages; a layer of loose mesenchyme that later forms a precursor of parietal bones; the precursors of the maxilla bones.

St.31: The precursors of the dermatocranial elements, including the parietal.

MyoD

St.14/15: Precursor cells of each jaw muscle in the first pharyngeal arch; eye muscle precursors.

St.14/15: The primordia of jaw and eye muscles.

St.26: The primordia of jaw and eye muscles.

St.17: Differentiated jaw and eye muscles.

St.17: Differentiated jaw and eye muscles.

St.29-31: Differentiated jaw and eye muscles.

Sox9

St.14/15: Cartilage precursors that later differentiate into the quadrate, Meckel's cartilage, and the braincase.

St.14/15: Precursor cells of the braincase, quadrate, and Meckel's cartilages.

St.26: The precursors of quadrate and Meckel's cartilages and the braincase; a layer of mesenchyme surrounding the brain laterally.

St.17: Differentiated chondrocranium and splanchnocranium components (the braincase, quadrate, and Meckel's).

St.17: Differentiated chondrocranium and splanchnocranium components (the braincase, quadrate, and Meckel's).

St.29-31: Differentiated chondrocranium and splanchnocranium components (the braincase, quadrate, and Meckel's).

Scx

St.14/15: Tendon precursor cells within jaw muscle primordia; connective tissue within eye muscles.

St.14/15: A layer of mesenchymal cells located at the periphery of the jaw adductor and eye muscle precursors.

-

St.17: Tendinous tissues accompanying jaw muscles; connective tissue associated with eye muscles.

St.17: Tendinous tissues at the periphery of jaw adductor muscles; the precursor of the bodenaponeurosis (central tendon of external adductor) within the jaw adductor muscular tissue.

Six2

St.14/15: The mesenchyme surrounding the eyes and cartilaginous precursors of the braincase, quadrate, and Meckel's; the mesenchyme between jaw muscle precursors and the skeletal tissues to which the muscles attach; the mesenchyme that dorsally surrounds the brain.

St.14/15: The mesenchyme surrounding the eye; the mesenchyme associated with the braincase and jaw cartilages; the mesenchyme within the jaw muscle precursors.

-

St.17: The mesenchyme localized around the jaw articulation between quadrate and Meckel's; the mesenchyme associated with the braincase, postorbital bone, and jaw muscles.

St.17: The mesenchyme surrounding jaw adductor muscles, braincase, and jaw cartilages.

Bmp4

St.14-17: The epithelium of cochlear

canal; the mesenchyme surrounding the eye; the mesenchyme distributed in the medial part of jaw primordia; the precursors of the palatine bones; a population of mesenchymal cells covering the brain dorsally.

St.14-17: The epithelium if cochlear canal; The mesenchyme dorsolateral and ventrolateral to the eye; a limited population of the mesenchyme in close proximity of the jaw articulation.

-

Msx1

St.14-17: The epithelium of the cochlear canal; the mesenchyme adjacent to the jaw articulation; the mesenchyme lateral to the quadrate and Meckel's cartilages; a thin layer of mesenchymal cells covering the brain dorsally.

St.14-17: The epithelium of the cochlear canal; the mesenchyme adjacent to the jaw articulation; the mesenchyme lateral to quadrate and Meckel's cartilages; the mesenchyme that populates the domain dorsal to the eye.

-

Msx2

St.14/15: A thin layer of mesenchymal cells surrounding the dorsal aspect of the brain; the mesenchyme located dorsal to the eye; the mesenchyme occupying the domain between the ventrolateral part of quadrate cartilage and surface epidermis.

St.14-17: Mesenchymal cells populating lateral aspect of the head (lateral to external adductor muscle).

St.26: The mesenchyme medial to the quadrate precursor; a mesenchymal layer surrounding the brain dorsally.

St.17: A population of mesenchymal cells in close proximity of postorbital and quadratojugal bone precursors; a thin layer of the mesenchyme surrounding the brain dorsally where future parietal bones form.

St.29: The precursors of palatine and pterygoid bones; the mesenchyme accompanying jaw cartilages; a layer of loose mesenchyme that later forms a precursor of parietal bones.

St.31: The precursors of the dermatocranial elements, including the parietal.