front matter 1

Posterior

edge of

white

matter

Posterior

edge of

gray

matter

Anterior

edge of

white

matter

Anterior edge

of gray matter

Anterior

edge of

gray

matter

Lumbar

Enlargement

Cervical

Enlargement

Thoracic

area

Sacral

area

Central canal

(defines midline)

Right Left

Medial motor columns

Lateral motor

columns

(cervical)

Lateral motor

columns

(lumbar)

A B

C

Figure 12. The entire spinal cord in specimen

M2050 (GW8.5, CR 36 mm) as viewed from the

front and top (A, B, C, this page) or the upper

right side (D, E, F, facing page). The front edge

of the reconstruction is section 730, the back edge

is section 2674. The total length after fi xation is

19.44 mm. In this and the following reconstruc-

tions, the spinal cord has been enlarged 3 times

more crosswise than lengthwise. Otherwise, the

model is too long to see the various motoneuron

columns clearly. Solid outlines defi ne the outer

edges of the white matter (transparent envelope, A

and D); dashed outlines defi ne the outer edges of

the gray matter (less transparent envelope, B and

E). The gray-white solid in panels A-E is the cen-

tral canal. The colored solids in panels A-E are

ventral horn motor columns.

There are seven distinguishable pairs of motor col-

umns in this specimen. The medial motor columns

(cyan) extend throughout the entire length of the

spinal cord. There are four lateral motor columns

in the cervical region, a short one (light brown) in

the upper cervical and three (yellow, orange, red)

in the cervical enlargement. The ventral to dorsal

stacking of the lateral motor columns is more easily

observed in the side views (especially panel F).

At this stage of development, the lumbar enlarge-

ment is not prominent and contains only two lateral

motor columns (purple and pink).

FIGURE 12 Top Front View GW8.5, CR 36 mm, M2050