front matter 1

Roof plate

Floor plateFloor plate

Dorsal neuroepithelium

Intermediate

neuroepithelium

Ventral

neuroepithelium

Ventral funiculus

First evidence of

vascularization in the

ventral neuroepithelium

First evidence of

vascularization in the

ventral neuroepithelium

Dorsal canal

Central

canal

Ventral canal

Settling

ventral horn

motoneurons

Settling

ventral horn

motoneurons

Migrating

ventral horn

motoneurons

and inter-

neurons

Earliest dorsal horn neurons

(laminae I and IV)

Earliest

intermediate

interneurons

Primordial

white matter

Roof plate

Floor plate

Diamond-shaped

spinal canal

expanding

dorsally and

ventrally

Dorsal root ganglion

Dorsal root boundary cap

Ventral root

Ventral horn Spinal nerve

Expanding gray

matter

Expanding white

matter

Expanding white

matter

Lateral plate (neuroepi-

thelium, NEP cells)

Oval bundle of His

(dorsal root bifurca-

tion zone)

Sulcus limitans

Dorsal funiculus

Large arrows extending from
the neuroepithelium indicate
many migrating neurons. Pro-
gressively smaller arrows
extending from the neuroepi-
thelium indicate progressively
fewer migrating neurons.
Arrows in the spinal canal indi-
cate the direction of expansion.

PLATE 5B