Transverse sections showing IHC for SOX9 in multiple stages of quail, chick, and peafowl embryos in (A, B) HH7 (not obtained for peafowl), (C–E) HH8, (F–H) HH9, and (I–K) HH11. Dorsal is to the top and ventral is to the bottom. SOX9 is expressed in quail at HH7 in the neural plate border/dorsal neural tube (compare B to A), but we were unable to obtain peafowl sections at this stage to compare. SOX9 is expressed in the dorsal neural tube during neurulation/NC specification at HH8 in all three organisms (C–E), is expressed in premigratory and migratory NC cells at HH9 during EMT (F–H), and is maintained in the dorsal neural tube in a small number of premigratory NC cells (most prevalent in peafowl), but is highly expressed in migratory NC cells at HH11 (I–K). Scale bars are 50 μm and are as marked in first panel of each row. (L) The number of SOX9+ cells were quantified for HH8 and HH9. At HH8, quail expressed more SOX9+ cells than chick (p = 0.0001) and peafowl (p = 0.0001), but by HH9 this difference was no longer statistically significant (p = 0.997). Ordinary one-way ANOVA statistical test used. (M) Cell migration was measured from the neural tube midline to the furthest migrated cell for HH9 and HH11. No statistical significance was observed, except between quail and peafowl at HH9 (p = 0.0373). Scale bar is marked in the first image of each row.