(a)
(b)
(c)
(d)
(e)
(f)
Figure 4: Schematic figure showing progressive developmental stages of the mouse embryo and sections through the PNP at these stages. (a) Schematic of embryo at 6–10-somite stage, which has already undergone closure (1); (b) section through PNP of (a), depicting Mode 1 neurulation; (c) schematic of embryo at 12–15-somite stage; (d) section through PNP of (c) exhibiting Mode 2 neurulation; (e) schematic of embryo which has undergone closures (1), (2), and (3) with PNP being the only remaining unfused section of the neural tube; (f) section through PNP of (e) depicting Mode 3 neurulation.