front matter 1

Sp

in

o

c

e

p

h

a

li

c

tr

a

c

t

s

Sp

in

o

c

e

p

h

a

li

c

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VVentral funiculusentral funiculus

Ventral corticospinal tract?

Central canal

surrounded by ependyma

Central canal

surrounded by ependyma

VVentral grayentral gray

Intermediate grayIntermediate gray

Dorsal root

bifurcation zone

Fasciculus cuneatus

Fasciculus gracilis

Dorsal root

collateralization zone

Lissauer's tract

Lateral

funiculus

Lateral

funiculus

Lateral
corticospinal tract
(myelinated)
(myelinating)

Tectospinal tract?

Medial longitudinal fasciculus?

Vestibulospinal tract?

Dorsal

gray

Dorsal

gray

Dorsal root

Dorsal funiculus

Myelinated

terminals of

dorsal root

collaterals

Myelinated

terminals of

dorsal root

collaterals

Myelinated axons

from dorsal root afferents,

intraspinal tract afferents,

and ventral motoneuron efferents

Subgelatinosal pleSubgelatinosal plexusxus

Reticulated areaReticulated area

S

p

i

n

o

c

e

r

e

b

e

l

l

a

r

t

r

a

c

t

s

S

p

i

n

o

c

e

r

e

b

e

l

l

a

r

t

r

a

c

t

s

I

n

t

r

a

s

p

in

al tr

a

c

t

s

I

n

t

r

a

s

p

in

al tr

a

c

t

s

myelination

gradient

myelination

gradient

myelinationmyelinationgradientgradient

Ventral median fissure

Dorsal median septum

Dorsal intermediate septum

VVentral gray commissureentral gray commissure

VVentral white commissureentral white commissure

Lateral

reticulospinal

tract?

Lateral

reticulospinal

tract?

See the matched cell body stained section in Plates 105A and B

The myelinating axons in the most superfi cial region of the lateral corticospinal tract extend to lumbosacral levels where they are

unmyelinated (see Plate 116). The lighter staining in the most superfi cial region of the spinocephalic tracts is occupied by axons

having cells of origin at lumbosacral levels where these axons are myelinated (see Plate 116). Both gradients indicate that myelina-

tion proceeds from proximal to distal in axons.

As stated in the previous specimens, the fi ne dashed lines in the lateral and ventral funiculi segregate regions of differing densities

of the myelin stain, not the borders of fi ber tracts. In this 4-month-old infant, the ventral and lateral funiculi contain dense staining

indicative of advanced myelination. There are three lightly stained areas: sparse reactive glia in the most superfi cial part of the

spinocephalic tracts, a myelinating region in the superfi cial part of the lateral corticospinal tract, and a thin unidentifi ed myelinating

region just medial to the spinocerebellar tracts. Most of the lateral corticospinal tract cannot be distinguished from the rest of the

lateral funiculus by its myelination pattern.

PLATE 104B