front matter 1

GW 8.5

CERVICAL

ENLARGEMENT

THORACIC

LUMBAR

ENLARGEMENT

SACRAL

GW10.5 GW19

See Plate 15

See Plate 17

See Plate 23

See Plate 25

See Plate 40

See Plate 42

See Plate 19 See Plate 27 See Plate 44

See Plate 20 See Plate 28 See Plate 45

53.89%

38.41%

2.95% 3.41%

.78% .57%

52.6%

45.1%

.5% .7%

.7% .4%

50%

49%

CC .1%

RP .2% EP .5%

FP .2%

53.6%

44.2%

CC 0.17%

RP 1.14% EP 0.69%

FP 0.20%

69%

29.4%

CC .3%

RP .6% EP .6%

FP .1%

72%

26%

CC 0.1%

RP 1.0% EP 0.9%

FP 0.1%

52%

43%

1% 2%

1% 1%

49%

40%

2% 5%

3% 1%

56%

41%

.7% 1%

.8% .5%

50%

40%

2% 7%

1% 1%

53%

31%

3%

10%10%

2% 1%

54%

33%

3%

7%7%

2% 1%

FLOOR PLATE (FP)

WHITE MATTER CENTRAL CANAL (CC) ROOF PLATE (RP)

GRAY MATTER EPENDYMA (EP)

Figure 36. Pie charts showing the proportional areas of the white matter (white), gray matter (gray), central canal (light green), ependyma (dark green),
roof plate (orange), and fl oor plate (red) at the cervical enlargement level (row 1), thoracic level (row 2), lumbar enlargement level (row 3), and the
sacral level (row 4). Each column contains measured sections from the same specimen: column 1 is M2050, GW8.5; column 2 is Y380–62, GW10.5;
and column 3 is Y52–61, GW19. The plate numbers in each square refer to the illustration of the measured section in previous parts of this atlas. By
following the shifting values of the proportional areas within a column, a gradient of maturation is evident between cervical enlargement to sacral levels.
The size of the ependyma increases in the fi rst two columns, indicating that the greatest degree of maturation is at the cervical enlargement level followed
by declining levels of maturation at thoracic, lumbar enlargement, and sacral levels. By GW19, the central canal, ependyma, roof plate, and fl oor plate
have very small proportional areas indicating the greater maturation of the spinal cord throughout its length at this time. The proportion of gray matter to
white matter generally increases from cervical enlargement to sacral levels at all ages. That is because descending fi ber tracts from the brain arrive fi rst
at cervical levels and progressively later at successively lower levels. Thus from GW8.5 to GW19, the white matter at the lumbar enlargement and sacral
levels is less mature than it is at the cervical enlargement level.

FIGURE 36 Level Differences in Proportional Areas: GW8.5-GW19