front matter 1

Roof plateRoof plate

Floor plateFloor plate

Dorsal neuroepithelium (alar plate)

Intermediate neuroepithelium

Ventral neuroepithelium (basal plate)

Slit-shaped spinal canal

Mitotic figures in neuroepithelium

Earliest differentiating motoneurons?

Primordial white matter

Roof plate

Floor plate Notochord

Slit-shaped spinal canal expanding ventrally

Somite

Primordial Dorsal root ganglion white matter

Lateral plate (neuroepithelium, NEP cells)

LATERAL PLATE

Large arrow extending from the neuroepithelium indicates migrating neurons.
Small arrow in the spinal canal indicates the direction of expansion.

PLATE 2B