front matter 1

A

B

CR 36 mm, M2050

CR 56 mm, Y380-62

1 mm

1 mm

Floor plate

Roof plate

Central

canal

Gray matter

Dorsal

Intermediate

Ventral

Subdivided

gray matter

Dorsal

horn

Intermediate

gray

Ventral

horn

Subdivided

neuroepithelium

Ependyma

Ependyma

Undivided

neuroepi-

thelium













Figure 6. Enlarged views of the CR 36 mm (A) and CR 56 mm (B) specimens (note scale differences). The top views show only the

surface features of the neuroepithelium on the right side; bottom views show the adjacent gray matter on the right side. In A, all parts

of the neuroepithelium are relatively smaller than in previous specimens but the dorsal neuroepithelium (still with many undulations,

downward arrowheads) is active. The bulges in the outer surface of the ventral horn (upward arrowheads) extend throughout its

entire length representing the advancing segregation of the ventral motoneurons into columns at all cervical levels. In B, the neuroepi-

thelium has been transformed into an ependyma that surrounds a considerably smaller central canal. The outer surface of the ependyma

is smooth. The dorsal horn has grown relatively larger and reaches the same size as the ventral horn.

Neuroepithelium and Gray Matter – GW8.5 to GW14 FIGURE 6