| The mesoderm then lies immediately beneath the ectoderm, with the endoderm lining the roof of the archenteron, the future gut. |
| In this tissue, therefore, the fate of some of the cells has been changed from prospective gut endoderm to mesoderm and ectoderm. |
| The mouth and pharynx are derived by a secondary infolding of superficial ectoderm called the stomodeum. |
| The branchial arches begin as cylindrical cores of mesenchyme sandwiched between continuous sheets of epidermal ectoderm and internal endoderm. |
| The critical process depends upon whether the ectoderm can contact a condensate of specialized mesenchyme called the dermal papillae. |
| The tip of the optic stalk is a considerable distance from the surface ectoderm. |
