Cephalic Neural Crest and Placodes

1 Introduction.- 2 Review of Literature.- 2.1 Areas of Thin and Thick Ectoderm.- 2.2 Placodes.- 2.3 Origin of the Differences in the Thickness of the Ectoderm.- 2.4 Conclusions.- 3 Methods.- 3.1 Animals.- 3.2 Fixation and Preparation.- 3.3 Selection of Embryos.- 3.4 Reconstruction.- 3.5 Mapping Out Different Ectodermal Areas.- 4 Observations.- 4.1 Presomite Stage, 7-Day Embryo.- 4.2 0–1 Somite Stage, 7 1/2-Day Embryo.- 4.3 3-Somite Stage, 7 1/2-Day Embryo.- 4.4 5-Somite Stage, 8-Day Embryo.- 4.5 6-Somite Stage, 8-Day Embryo.- 4.6 7-Somite Stage, 8-Day Embryo.- 4.7 8-Somite Stage, 8 1/2-Day Embryo.- 4.8 10-Somite Stage, 8 1/2-Day Embryo.- 4.9 11-Somite Stage, 9-Day Embryo.- 4.10 17-Somite Stage, 9 1/2-Day Embryo.- 4.11 21-Somite Stage, 10-Day Embryo.- 5 Discussion and Conclusions.- 5.1 Interpretation of the Observations.- 5.2 General Structure of the Embryos.- 5.3 Development of the Ectodermal Mesenchyme of the Head, the Cephalic Neural Crest.- 5.4 Regional Development of the Ectoderm of the Head.- 5.5 Development of Placodes.- 5.6 Genesis of the Local Differences in Thickness of the Ectoderm of the Head.- 6 Summary.- References.