Table 1. Landmark definitions for avian embryos.
Paired landmarks are indicated by two numbers separated by /.
| Landmark | Definition |
|---|---|
| 1 | Deepest midline point in 3-way junction between forebrain hemispheres and midbrain |
| 2 | In standard lateral orientation*: Point along the midline curve between forebrain hemispheres, when the curve changes from largely horizontal to largely vertical. |
| 3 | Deepest point in 4-way junction between medial nasal processes and the base of forebrain hemispheres |
| 4 | Point at midline tip of frontonasal process, at point of greatest curvature between vertical (frontonasal) and horizontal (palatal) aspects (in embryos sub-HH25) [In embryos HH25 and older, this is a pointy tip, so place landmark at inferior-most midline point on tip] |
| 5/17 | Point at border between forebrain and nasal processes that is directly superior to the most superior point of nasal pit |
| 6/18 | Point at inferior-posterior corner of forebrain (meeting of vertical and horizontal seams) |
| 7/19 | In standard lateral orientation: Point on superior-most edge of eye |
| 8/20 | Point at edge of eye, that exists at the end of the valley between lateral nasal process and maxillary process |
| 9/21 | Point at edge of lens placode/lens pit, placed in alignment with the valley between lateral nasal process and maxillary process |
| 10/22 | In standard lateral orientation: Point on inferior-most edge of eye |
| 11/23 | Point at inferior tip of lateral nasal process, taken along midline of the lateral nasal process |
| 12/24 | Point at inferior-lateral tip of medial nasal process/FNP |
| 13/25 | Point at superior border of nasal pit |
| 14/26 | Point at juncture between palate, mandibular process, and maxillary process (Works best at younger stages (HH22–25), will be obscured at older stages (above HH25) by potential pockets of fluid scanned with the specimen) |
| 15/27 | Inferior point of maxillary process, taken along the midline of the maxillary process |
| 16/28 | Anteriormost point on the midline of the maxillary process |
*
Standard Lateral Orientation: View the embryo with the eye in the center of view. For younger embryos, make the anterior curve of the forebrain as vertical as possible. For older embryos, when the anterior forebrain is rounder, make the line between the anterior extent of the forebrain and the point (#3) at the midline border of the forebrain and medial nasal processes (developing beak) as vertical as possible.