(a,c) E18 ferret embryo, 40 somites. The telencephalic midline (Dml) is evident in the E18 ferret (c), and an olfactory plate (OfP) is developing. The Op is now indented (shadow in (a), and seen clearly in a more frontal view (c). The FLB is now obvious (a), a hind limb bud (HLB) condensation is visible, and a tail limb bud (TLB) can be identified by its inward curve. (b,d) E10.0 mouse embryo, 33 somites, shows similar features to the ferret embryo, including a markedly indented Op (d). The OfP is more prominent in mouse than in ferret (compare c, d). Scale bar in (a) is 1.0 mm for a,b; 0.5mm for c,d.