The rostral extremity of the neural tube closes in embryos with usually about 15-18 somite pairs and defines this stage. The otic pit becomes progressively more indented but not closed, the mandibular process of the 1st branchial arch is clearly visible. The 3rd branchial arch becomes visible late in the stage. An increasingly prominent ridge on the lateral body wall, approximately at the level of the 8th-12th somite, indicates the site of the future forelimb bud.

Absent: forelimb bud.

9 dpc (range 8.5-9.75)
13-20 somite pairs

All scale bars in microns

Click on an image for a larger version.