Sense organs

Eye

At S10, the rostral neuropore is still open. The optic primordium appears for the first time at the inner side of the anterior part of the diencephalon (neuromere D1) and forms an optic sulcus. The primordia of both sides are connected over the midline through the chiasmatic plate. At S11, the optic sulcus deepens and evaginates. At S12, this forms the optic vesicle which comes into direct contact with the surface ectoderm. The cavity of the optic vesicle (optic ventricle) joins with that of the diencephalon, which is the future 3rd ventricle, through the optic stalk. Mesenchymal tissue comes to lie between the surface ectoderm and parts of the optic vesicle.