Anterograde labeling of retino-retinal (A) and isthmo-retinal (B) axons in the flat-mounted right retina at E9. The photographs show the same retinal region close to the optic fissure (OF). Two of the retino-retinal axons (A) and one isthmo-optic axon (A, B, arrows) are in close vicinity to each other but are directed toward the retinal periphery. C–E, Typical intraretinal growth cones of isthmo-retinal axons labeled wtih 4Di-10ASP at E6 and observed in the whole-mounted retina at E9. Note the multiple filopodial protrusions. F, Typical isthmo-retinal terminal branching labeled with 4Di-10ASP at E6 and photographed at E13. Scale bars, 25 μm.