ABSTRACT
The Optic Stalk (4th Week) This grows out of the neural crest of the open forebrain region (Figure la). After crest fusion, the optic stalk is associated with a diencephalic area (Figure lb) that becomes the lateral geniculate body of the visual tract (6 months). The stalk grows laterally towards the head sur face, expanding into the optic vesicle (4 weeks). This abuts against head ectoderm causing the contacted area to change into the lens placode (columnar epithelium; Figure lb). This sinks into the optic vesicle, changing it into the optic cup (5th week, Figure lc). The lens pla code rounds up into the lens vesicle, and the lenticular pore closes (Figures lc and d).
