Figure 6.

Stages 13 and 14: Anterior–posterior axis reads left to right in both images. Scale bar = 1 mm. Stage 13 (2 ½ days). Stage 14 (2 ⅔ days). Abbreviations: ap, area pellucida; at, atrium of heart; bc, bulbus cordis; bi, blood islands; di, diencephalon; hn, Hensen’s node; lbf, lateral body of foregut; le, lens vesicle; mm, mesomere; ms, mesencephalon; mt, metencephalon; my, myelencephalon; nf, neural fold; no, notochord; nt, neural tube; opc, optic cup; ot, otic vesicle; pa, pharyngeal arch; rp, Rathke’s pouch; si, sinus terminalis; sm, somite mesoderm; te, telencephalon; tf, tail fold; v, ventricle of heart; vit, area vitellina; vt, vitelline artery. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]