Talk:Paper - Comparative studies on the growth of the cerebral cortex 5 (1918)
COMPARATIVE STUDIES ON THE GROWTH OF THE CEREBRAL CORTEX V.
V. PART I. ON THE AREA OF THE CORTEX AND ON THE NUMBER OF CELLS IN A UNIT VOLUME, MEASURED ON THE FRONTAL AND SAGITTAL SECTIONS OF THE ALBINO RAT BRAIN, TOGETHER WITH THE CHANGES IN THESE CHARACTERS ACCORDING TO THE GROWTH OF THE BRAIN
V. PART II. ON THE AREA OF THE CORTEX AND ON THE NUMBER OF CELLS IN A UNIT VOLUME, MEASURED ON THE FRONTAL AND SAGITTAL SECTIONS OF THE BRAIN OF THE NORWAY RAT (mUS NORVEGICUS), compared WITH THE CORRESPONDING DATA FOR THE ALBINO RAT
NAOKI SUGITA From the Wistar Institute of Anatomy and Biologij
THREE FIGURES AND FOUR CHARTS
PART I
I. INTRODUCTION
The present study is an extension of an earlier one on the thickness of the cerebral cortex in the albino rat (Sugita, '17 a) and aims to present the extent of the actual area occupied by the cortical cells, as seen in sections which were taken from the fixed levels of the albino brain, and also to follow the changes in this area during the postnatal growth of the brain. In the course of this investigation, the number of nerve cells contained in a unit volume of a fixed locahty in the frontal i section was counted and the changes in this number with advancing age were ascertained. Furthermore the relation between the cell number and the cortical area was critically examined.
For this study, the sections, which had been previously used for the investigation of the thickness of the cortex of the albino rat brain, were again utilized. The material, amounting to 78
61
THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 29, NO. 2 APRIL, 1918
62 NAOKI SUGITA
albino rats, sexes combined, which was used in the present study, is identical with that listed in table 1 of the former paper (Sugita, '17 a), to which the reference should be made for this studyalso.
These studies were made during the winter semester of 19161917.
II. MEASUREMENTS AND ENUMERATIONS
A. Area of the cortex in the sagittal section
As previously described (Sugita, '17 a), the sagittal section (fig. 1) was taken in a plane passmg through the frontal pole afid parallel to the mesial surface of the hemisphere. This section from each individual brain was projected on a sheet of paper by the Leitz-Edinger Projection apparatus, at a magnification of exactly twenty diameters, and the outline of the image then accurately traced on the sheet. At the transitional part of the cortex at the frontal pole to the olfactory bulb and at the subiculum, where the cortex goes over into the structure of the cornu Ammonis, the borderlines were drawn along the radiation of the cells in those parts (fig. 1). The anterior borderline (a-a') is formed by a prolongation of the line bounding the dorsal surface of the olfactory bulb. The posterior borderline (p-p') is clearly located, because this was drawn at the point where the thickness of the ganglionic layer abruptly diminishes at the beginning of the ganglion cell band characteristic for the cornu Ammonis. The area of the cortex, including the lamina zonalis, which contains no proper nerve cells, was then repeatedly measured to a square millimeter on the drawing, using the Ott Compensating Planimeter. The values obtained were then averaged, and 1/400 of the value, which corresponds to the cortical area on the slide, was recorded. This value was then converted into that for the fresh condition of the material, by the following procedure.
On the outline, which was taken from the section on the slide, the diameter from frontal pole to the occipital pole (L. F) was measured and reduced, and, according to the formula given in the former paper (Sugita, '17 a), which reads
GROWTH OF THE CEREBRAL CORTEX
63
Correction-coefficient =
The diameter L. F in fresh cerebrum
The diameter L. F on the shde the correction-coefficient was determined. The value for the area obtained by the (first) direct measurement from the slide was then corrected to the corresponding value for the fresh condition of the material, by multiplying by the square of the correction-coefficient. The corrected values thus obtained are given in the last column of table 1.
The values for the cortical areas in the respective sagittal sections of each individual were then grouped according to the
Fig. 1 Showing, by shading, the cortical area measured on the sagittal section of the albino rat brain. The anterior borderline ((a-a') is formed by a prolongation of the line bounding the dorsal surface of the olfactory bulb. The
posterior borderline {p-p') is drawn at the point where the ganglionic layer goes
over abruptly to the ganglion cell band in the cornu Ammonis.
brain weight, into twenty groups, as in the other studies of this series, and the average value for each group was found. The average areas of the cortex in the sagittal section for each group (table 1) were plotted in chart 1 (graph s), which shows the increase in area according to the increase in brain weight.
B. Area of the cortex in the frontal section
The frontal section (fig. 2) was cut in the plane passing through approximately the middle point of the mesial surface of the
64
NAOKI SUGITA
TABLE 1
Shoiving the observed and corrected values of the area of the cerebral cortex in the sagittal section of the albino rat brain, accompanied by the data for the correctioncoefficient in the individual cases and the correction-coefficient for the group. L. F is the longitudinal diameter of the cerebrum
BRAIX WEIGHT
OBSERVED
AREA OF CORTEX
CORRECTION-COEFFICIENT
CORRECTED
GROUP
L. F in fresh
brain
The same on
slide
AREA
OF CORTEX
grams
mm.
mm.
mm.
mm."^
la
0.153
3.2
5.50
4.97
4.1
c
0.154
3.0
5.60
4.80
4.1
b
0.177
4.0
5.70
5.13
4.9
0.161
5.4
1.
13^
4.4
II a
0.213
4.0
5.80
5.13
5.1
b
0.221
3.9
6.00
5.43
4.8
c
0.261
4.8
6.60
5.60
6.7
d
0.271
4.8
6.75
5.80
6.5
e
0.288
4.5
6.70
5.75
6.1
■ (Birth)
0.251
4.4
1.
15-^
5.8
III a
0.311
6.1
7.35
6.45
7.9
1)
0.322
6.3
7.20
6.40
8.0
g
0.374
8.1
7.40
7.40
8.1
c
0.390
6.7
7.50
6.70
8.4
i
0.395
7.4
7.95
7.20
9.0
0.S58
6.9
1.
10^
8.3
IV b
0.400
6.7
7.70
6.65
9.0
a
0.402
8.4
7.75
7.30
9.4
e
0.420
8.2
7.95
7.20
10.0
i
0.443
10.6
8.30
8.10
11.1
d
0.459
8.8 •
8.05
7.60
9.9
e
0.466
9.6
8.40
7.80
11.1
0.^32
8.6
/.
082
10.1
Vi
0.501
10.2
8.35
7.90
11.4
a
0.525
12.7
8.55
8.45
12.9
b
0.528
11.1
8.50
8.05
12.4
c
0.534
9.0
8.65
7.60
11.6
d
0.537
10.1
8.30
7.70
11.7
e
0.555
12.3
9.25
8.65
14.0
f
0.558
11.0
9.20
8.50
12.9
g
0.564
11.4
8.85
8.40
12.7
h
0.579
11.5
9.10
8.35
13.6
0.542
11.0
1.07'^
12.6
GROWTH OF THE CEREBRAL CORTEX
65
TABLE 1— Continued
BRAIN WEIGHT
OBSERVED
ARE.\ OF CORTEX
CORRECTION-COEFFICIENT
CORRECTED
GROUP
L. F in fresh
brain
Th
e same on
slide
AREA
OF CORTEX
(/rams
mm."
m m .
??i m .
?« m .2
VI c
0.610
12.0
9.35
8.35
14.9
a
0.617
10.7
9.25
7.95
14.4
e
0.090
15.0
9.60
9.00
17.1
0.639
12.6
1.
ir
15.5
VII a
0.740
15.7
10.50
9.80
18.1
b
0.760
11.5
10.65
8.50
18.1
0.750
13.6
1.15-'
18.1
VIII a
0.800
14.4
10.50
9.25
18.5
h
0.805
13.8
10.90
9.20
19.4
b
0.822
16.2
10.45
9.60
19.2
c
0.849
18.0
10.50
9.70
21.1
k
0.870
15.1
10.95
9.40
20.5
d
0.898
17.0
11.45
10.15
21.6
0.841
15. S
1.13^
1
20.1
IX d
0.959
17.9
11.60
10.50
21.8
e
0.960
16.9
11.40
9.85
22.5
a
0.972
15.4
11.30
9.70
20.9
(10 days)
0.964
16.7
/.
W
21.7
X a
1.033
13.9
11.90
9.40
22.3
b
1.036
15.9
11.85
9.85
23.1
e
1.051
17.5
12.05
10.05
25.0
1.040
15.8
1.
22"
23.5
XI a
1.107
17.3
12.00
10.00
25.2
b
1.189
18.8
12.50
10.25
28.0
c
1 . 193
19.1
12.65
10.50
27.8
d
1.195
16.0
12.60
10.00
25.4
(20 days)
1.171
17.8
1.22'
1
26.6
'XII c
1.234
18.4
12.30
10.35
26.0
a
1.273
15.7
12.45
9.65
26.2
1.253
17.1
1.
2J,'
26.1
XIII a
1.301
18.7
13.00
11.10
25.7
g
1.307
15.6
12.95
10.00
26.2
b
1.327
17.2
13.20
10.50
27.2
c
1.346
17.8
13.00
10.10
29.5
h
1.392
21.9
13.45
11.60
29.5
1.335
18.2
1.2S'
27.6
66
naoki sugita
TABLE \— Concluded
BRAIN WEIGHT
OBSERVED
AREA
CORTEX
CO RRECTION-COEFFICIENT
CORRECTED
GROUP
L. F in fresh
brain
The same on
slide
AREA
OF CORTEX
grams.
mm.
mm.
mm.
mm. 2
XIV a
1.412
17.5
13.40
10.40
29.1
e
1.441
15.2
13.25
10.10
26.2
b
1.483
21.1
13.30
11.30
29.3
1.U5
17.9
1.
26^
28.2 ■
XV a
1.530
17.4
13.70
10.80
28.1
b
1.542
19.6
13.50
11.40
27.5
c
1.552
17.2
13.70
10.65
28.6
d
1.573
20.0
13.70
11.15
30.1
e
1.574
18.9
13.75
11.05
29.3
1.554
18.6
l.£
4'
28.7
XVI a
1.642
18.9
14.10
11.30
29.4
g
1.643
18.7
14.65
11.60
29.7
c
1.647
18.7
13.75
11.05
29.0
e
1.690
17.5
13.65
10.70
28.6
1.656
18.4
1.
26^
29.2
XVII f
1.720
18.3
14.90
11.60
30.2
a
1.721
18.4
13.90
10.90
29.8
b
1.730
23.5
13.85
11.70
32.8
c
1.731
20.8
14.30
11.60
31.7
1.726
20.2
1.
u^
31.1
XVIII c
1.817
18.5
15.20
11.50
32.4
a
1.844
24.7
14.00
12.10
33.0
e
1.855
21.6
15.05
12.15
33.1
1.839
21.6
1.
24^
32.8
XIX a
1.924
20.6
15.40
12.30
32.3
i.m
20.6
1.
25^
32.3
XX a
2.039
22.6
15.10
12.60
32.5
b
2.069
25.1
15.55
13.20
34.8
2.054
23.9
1.19'
33.7
hemisphere and cutting the corpus callosum, the conunissura anterior and the chiasma opticum (Sugita, '17 a). On the drawing of the outhne of the frontal section (fig. 2), which was traced
GROWTH OF THE CEREBRAL CORTEX
67
in the same manner as that for the sagittal section, the dorsal and the ventral borderlines of the cortical are^ were drawn. The dorsal border (d) was determined by the ectal borderline of the corpus callosum, which lies under the tip of the cortex at the bottom of the fissura sagittalis, and the ventral border {v-v') was drawn perpendicular to the surface at the basal end of the cell group which is found under the cortex proper just below the region of the fissura rhinalis, latero-basal to the cap
Fig. 2 Showing, by shading, the cortical area measured on the frontal section of the albino rat brain. The dorsal border (d) is chosen at the borderline of the corpus callosum. The ventral border (v-v') was drawn perpendicular to the surface at the basal end of the cell group found near the fissura rhinalis, latero-basal to the capsula externa. The double shaded part, locality VII, indicates the area where the cell number and cell size were determined.
sula externa. This latter border is not so sharply defined, but we could not find any better marking point than this cell group. The area of the cortex, thus bounded, was then measured and recorded. In making the measurement, the area of the cortex was at first measured and then the total area of the frontal section, — of one hemicerebrum — excluding the cavity of the lateral ventricle and the tractus opticus, was measured. The ratio of the cortical area to the total area of the section was then computed. Correction of the observed values to those for the
68
NAOKI SUGITA
fresh condition of the material was made in the same manner as for the sagittal cortex, by multiplying by the square of the value of the correction-coefficient. This latter was obtained by the formula given in a former paper (Sugita, '17 a), as follows:
The diameter W. D in fresh cerebrum
Correction-coefficient =
The diameter W. D on the slide
li 70 (,5 60 55 50 45 40 35 30 25 20 15 10 5
..-T
/
/'
^
'
~y
-;>-'
>
i^
^^
^'
v
i
'
1
t
i
■■/^
^,.--'
i 1 !
^
-^j
.--'
-'—
---^
! i
,y.
y
^.^
^^
s
/f
^'^
^
■^
/
i
^
■>^
i
^
^
'^
1 ■
s=
j i
\
1
'O 0.1 Q2 0.3 Q4 Q5 06 07 Q8 Q9 10 11 12 13 14 15 16 IT 18 19 2.0 ^s.
Chart 1 Showing the corrected areas of the cerebral cortex in the sagittal
and the frontal sections and the area of the whole frontal section, all according
to the brain weight, accompanied by the theoretical value of the last which is
assumed to be proportional to the square of the cube root of the brain weight.
Albino rat. X— • — ■ — • X, Cortical area in the sagittal section, o oof
Cortical area in the frontal section. • 'F, Area of the whole frontal section.
T, Theoretical area of the frontal section, i.e., the square of the
cube root of the brain weight. All graphs are based on the data in tables 1 and 2.
These data are all entered in table 2, in which the average measurements for each brain weight group are also given. The graphs for the total area of the frontal section (graph F) and for the area of the frontal cortex (graph f) in chart 1 are based on the corrected data given in table 2.
TABLE 2
Showing the observed and corrected values of the area of the cerebral cortex and of the total frontal section and the percentage of the cortical area to the total frontal section of the albino rat brain, accompanied by the data for the correction-coefficient in the individual cases and the correction-coefficient for the group. W. D is the frontal diameter of the cerebrum
OBSERVED
CORRECTIONCOEFFICIENT
CORRECTED
PERCENTAGE OF
BRAIN
WEIGHT
CORTICAL
GROUP
Area
of cortex
Area of
total section
W. D
in fresh brain
The same
on slide
Area
of cortex
Area of
total section
AREA IN
TOTAL
c SECTION
grams
mm. 2
mTO.2
mm .
m m .
»i m .2
vim.^
per cent
la
0.153
2.8
9.2
6.45
5.65
3.7
12.0
34
c
0.154
2.6
8.2
6.35
5.40
3.6
11.4
34
b
0.177
3.5
9.9
6.95
6.26
4.3
12.2
35
0.161
3.0
9.1
1.
W
3.9
11.9
35
II a
0.213
4.4
13.0
8.40
7.35
5.7
17.0
34
b
0.221
3.6
11.9
7.95
6.50
5.4
17.8
30
c
0.261
4.6
13.0
7.80
7.10
5.6
15.7
36
d
0.271
4.4.
13.1
7.75
6.80
5.7
16.9
34
e
0.288
4.1
11.8
8.55
7.05
6.0
17.4
35
(Birthj
0.251
4.2
12.6
1.
16"
5.7
17.0
34
III a
0.311
5.1
15.3
8.50
7.65
6.3
18.9
33
b
0.322
5.1
13.0
8.70
6.80
8.3
21 .2
39
g
0.374
7.2
19.0
8.95
8.40
8.2
21.6
38
c
0.390
6.5
15.9
8.85
7.60
8.8
21.5
39
i
0.395
7.5
17.8
9.10
8.60
8.4
20.0
42
0.358
6.3
16.2
1.13^
8.0
20.6
39
IV b
0.400
7.6
19.4
9.00
8.50
8.5
21.7
39
a
0.402
6.8
16.7
9.10
7.90
9.0
22.2
41
c
0.420
6.7
17.9
9.00
8.15
8.2
21. g
38
i
0.443
8.0
19.0
9.15
8.40
9.4
22.3
42
cl
0.459
6.9
17.2
9.50
7.95
9.8
24.5
40
e
0.466
9.4
21.8
9.30
9.25
9.5
22.1
43
o.m
7.6
18.7
l.W
9.1
22.4
41
Vi
0.501
9.0
22.3
9.80
9.20
10.2
25.3
40
a
0.525
9.8
22.4
9.65
9.10
11.0
25.2
44
b
0.528
8.7
19.6
9.90
8.60
11.5
26.0
44
c
0.534
7.6
18.6
10.30
8.25
11.4
29.0
39
d
0.537
8.8
20.1
10.00
8.80
11.4
26.0
44
e
0.555
9.9
22.5
9.90
9.00
12.0
27.2
44
f
0.558
9.2
20.0
10.00
8.55
12.6
27.4
46
g
0.564
10.2
22.9
10.10
9.15
12.4
28.0
44
h
0.579
10.1
22.1
10.10
9.05
12.8
27.6
46
0.542
9.3
21.2
1.13
11.7
26.9
u
69
TABLE 2~Continued
OBSERVED
CORRECTIONCOEFriCIENT
CORRECTED
PERCENTAGE OP
BRAIN
WEIGHT
CORTICAL
GROUP
Area
of cortex
Area of
total
section
W. D
in fresh brain
The same
on slide
Area
of cortex
Area of
total section
AREA IN
TOTAL SECTION
grams
WOT .2
invi.^
mm.
7)1 m.
TOOT.2
mm.
per cent
Vie
0.610
9.9
21.7
10.15
8.50
14.1
31.0
46
a
0.617
9.6
21.6
10.55
8.65
14.3
32.2
44
e
0.690
11.6
23.7
10.60
9.40
14.8
30.2
49
N
0.639
10.4
22.3
1.
19'
14.4
31.1
46
Vila
0.740
11.1
22.1
11.00
9.20
15.9
31.6
50
b
0.760
10.2
20.3
11.20
8.70
16.9
33.6
50
0.750
10.7
21.2
1.,
24'
16. 4
32.6
50
Villa
0.800
10.6
21.8
11.15
8.60
18.8
36.7
51
h
0.805
11.3
23.6
10.60
8.30
18.5
38.6
48
b
0.822
13.6
28.5
11.85
10.20
18.4
38.5
48
c
0.849
13.7
28.8
11.40
9.90
18.2
38.3
48
k
0.870
13.4
27.7
11.45
9.60
19.1
39.5
48
d
0.898
13.1
31.2
11.75
10.20
17.4
41.5
42
0.841
12.6
26.9
1.
202
18. 4
38.9
48
IX d
0.959
13.5
28.4
11.80
9.70
20.0
42.0
48
e
0.960
13.8
29.4
12.15
10.10
20.0
42.6
47
a
0.972
14.3
28.4
11.95
9.80
21.3
42.4
50
(10 days)
0.964
13.9
28.7
1.
2P
20.4
42. 3
48
Xa
1.033
14.1
30.3
12.40
10.30
20.4
44.0
46
b
1.036
13.4
30.5
12.40
10.15
20.0
45.5
44
e
1.051
13.2
25.9
12.10
9.40
21.8
43.0
51
1.040
13.6
28.9
1.
23'
20.7
44.2
47
XI a
1.107
13.7
28.7
12.90
10.20
21.8
45.7
48
b
1.189
13.3
27.8
13.15
10.30
21.7
45.4 '
48
c
1 . 193
14.6
30.8
12.70
10.30
22.2
47.0
47
d
1.195
12.8
27.2
12.50
9.80
21.0
44.5
47
(20 days)
1.171
13.6
28.6
1.
26^
21.7
45.7
48
XII c
1.234
15.0
31.9
12.95
10.70
22.0
46.8
47
a
1.273
11.9
23.6
12.90
9.10
24.0
47.5
50
1.25S
13.5
27.8
1.
3r
23.0
47.2
49
XIII a
1.301
13.9
28.3
13.20
10.25
23.0
47.1
49
g
1.307
13.9
29.9
12.70
10.00
22.5
48.3
47
b
1.327
12.2
28.2
13.35
9.70
23.2
53.3
43
c
1.346
13.3
29.0
13.15
9.85
23.7
51.8
46
h
1.392
16.3
34.8
13.10
10.90
23.6
50.3
47
1.335
13.9
30.0
1.29^
23.2
50.2
46
70
TABLE 2—Co7icluded
OBSERVED
CORRECTIONCOEFFICIENT
CORRECTED
PERCENTAGE OF
BHAIN
WEIGHT
CORTICAL
GROUP
Area
of cortex
Area of
total
section
W. D.
in fresh brain
The same
on slide
Area
of corte.x
Area of
total section
AREA IN
TOTAL SECTION
grams
mm. 2
m m .
171 m.
mm.
»»m.2
mm. 2
■per cent
XIV a
1.412
13.9
29.4
13.65
10.30
24.4
51.6
47
e
1.441
12.4
25.7
13.10
9.20
25.2
51.0
49
b
1.483
15.2
33.3
13.80
10.80
24.8
54.4
46
1445
13.8
29.5
1.34""
24.8
52.3
47
XV a
1.530
14.4
33.6
13.80
10.80
23.5
54.8
43
b
1.542
13.9
30.5
13.70
10.40
24.2
53.0
46
c
1.552
14.2
31.7
13.50
10.30
24.4
54.4
45
d
1.573
14.2
30.8
13.90
10.60
24.4
53.1
46
e
1.574
14.8
32.2
13.70
10.50
25.2
54.8
46
1.554
14-3
31.8
l.l
?02
24-3
54.0
45
XVI a
1.642
16.4
37.0
13.80
11.20
24.9
56.2
44
g
1.643
11.6
27.4
13.40
9.50
23.2
54.7
42
c
1.647
14.3
29.8
14.00
10.50
25.5
53.2
48
e
1.690
13.0
30.7
13.45
10.00
23.5
55.3
42
1.656
13.8
31.2
l.t
J32
24.3
54.9
44
XVII f
1.720
12.5
28.7
13.50
9.60
24.8
56.8
44
a
1.721
14.8
34.5
14.00
11.00
24.0
56.0
43
b
1.730
17.5
40.4
14.70
12.35
24.8
57.2
43
c
1.731
17.5
39.2
14.40
12.10
24.8
55.6
45
1.726
15.6
35.7
l.i
W
24.6
56.4
44
XVIII c
1.817
13.3
31.1
14.00
10.10
25.6
59.8
43
a
1.844
1.855
17.4
38.1
15.00
12.10
26.7
58.5
46
e
14.2
32.0
14.30
10.60
25.8
58.3
44
1.839
15.0
33.7
l.t
?^2
26.0
58.9
44
XIX a
1.924
14.8
33.9
14.10
10.90
24.8
57.0
44
1.924
U.8
33.9
l.i
w
2^.8
57.0
44
XX a
2.039
16.8
42.7
■ 14.80
12.10
25.2
63.9
39
b
2.069
15.7
40.3
14.60
11.70
24.5
62.8
39
2.054
16.3
41.5
1.23'
24-9
63.4
39
C. Number of nerve cells
On the frontal sections used for the measurement of the cortical area, the number of nerve cells contained in a unit volume at a fixed locality in the cortex was counted. The locality selected was at the middle part of the cortical band (fig. 2, VII), designated as locality VII in figure 4 in a former paper (Sugita,
71
72 NAOKI SUGITA
'17 a). To represent the cortex, the lamina pyramidaHs and the lamina ganglionaris were selected. By the use of the ocular net-micrometer (with Zeiss Comp. Ocular 6 and Zeiss objectives 2 mm. and 4 mm.), the number of nerve cells in five adjoining squares along the cortical band, each square 100 micra on a side, was counted in a given location. The numbers obtained were added together and then, by multiplying by two, was converted to the number in a unit area of 0.1 mm.- on the section. This value, the number of nerve cells in a slice of cortex, 0.1 mm." in area and 10 micra thick (the thickness of the section) or 0.001 mm.^ in volume, was then reduced to the number in this volume in the fresh condition of the brain. To make this reduction, I used as the correction-coefficient the cube of the reciprocal of the correction-coefficient obtained by the for The diameter W. D in fresh cerebrum , . , , , ,
mula: =- v-. -— — 7r\ ' which had been
1 he diameter W . D on the slide
previously employed, because the section on the slide was assumed to have shrunken in all three dimensions equally at the rate of the correction-coefficient and therefore a unit volume in the fresh condition would correspond to the volume of the unit on the slide multiplied by the cube of the reciprocal of the correction-coefficient.
In the lamina pyramidalis, the pyramids are more densely crowded at the ectal than at the ental part of the lay?r, which adjoins the lamina granulans interna. I adjusted the upper line of the net-micrometer squarely on the border between the lamina zonalis and the lamina pyramidalis and counted the cell number included in a square, 100 micra on each side, at the ectal part of the layer, where the cells are crowded densely. If large blood vessels appeared in the microscopic field, I gave up such a field and counted an adjoining one where no large vessels were present.
In the lamina ganglionaris the large ganglion cells are mixed with a number of small pyramids, almost equal in size to, or somewhat smaller than, the pyramids in the lamina pyramidalis. At first, the number of all the nerve cells, the large and small combined, was counted. Then the large ganglion cells, which
GROWTH OF THE CEREBRAL CORTEX 73
surely represent a group distinct from the small pyramids, were counted alone. So, by subtraction, the number of small pyramids only in the lamina ganglionaris was obtained. In counting the ganglion cells, I adjusted the lower line on the net-micrometer accurately on the border between the lamina ganglionaris and the lamina multiformis, because between the lamina ganglionaris and the lamina granulans interna there is found a pale band poor in cells and therefore it was not convenient to adjust the upper line of the net-micrometer at this border. The number of cells observed, in a slice of 0.1 mm.'- in area and 10 micra thick on the slide, were in the similar manner recorded and by the use of the same correction-coefficients, as were used in the case of the pyramidal cells, were reduced to the number for the fresh condition of the brain.
Out of the total number of cells, which came in view in the microscopic field, about one-third does not contain the nucleoli in the cell nuclei. This means that the nucleoli in question lie outside of the section. Nevertheless I counted the cells having nuclei without nucleoli together with those in which nucleoli were to be seen, because my object was to ascertain the cell density in the locality chosen and not to determine the total number of nerve cells in a series of sections. In the latter case, the double counting of one and the same cell must be necessarily avoided. On the other hand, the cells which were represented in the section by only fractions of the cell bodies without nuclei were omitted from the counting. The number of such cells was small. Neuroglia nuclei, which were to be easily distinguished by their smaller size, and the intima cells of the capillaries, if they came in view, were not counted.
Table 3 shows the results of these enumerations.
III. DISCUSSION
D. The area of the cortex in the sagittal section
Examinmg table 1 and chart 1 (graph s), which give the area of the cortex in the sagittal sections of the albino rat brain, it is seen that the area increases steadily with increasing brain weight.
TABLE 3
Giving for each individual and for each brain weight group the number of nerve cells in 0.001 vim.^ in volume of the cortex, in the lamina pyramidalis and in the lamina ganglio7iaris, and also the mimber of the ganglion cells in the lamina ganglionaris, all counted at the middle part of the cortex in the frontal section, as shown in figure 2. Albino rat
BRAINWEIGHT
CORRECTIONCOEFFICIENT
NUMBED
OF CELLS
IN A VOLUME OF CORTEX, 0.001 MM.^
GROUP
\V. D
in fresh brain
W.D
on slide
Lam. pyramid.
Lam. ganglion.
Ganglion cells in
lam. gangl.
Observed
Corrected
Observed
Corrected
Observed
Corrected
grams
mm.
m m .
la
0.153
6.45
5.65
1150
775
c
0.154
6.35
5.40
1130
695
b
0.177
6.95
6.26
945
690
0.161
(1/1
14)'
1075
720
II a
0.213
8.40
7.35
830
556
370
248
91
61
b
0.221
7.95
6.50
930
509
393
215
114
62
c
0.261
7.80
7.10
735
554
322
242
104
78
d
0.271
7.75
6.80
726
490
358
242
114
77
e
0.288
8.55
7.05
715
402
424
238
120
67
(Birth)
0.251
(1/1
ley
787
502
373
237
109
69
Ilia
0.311
8.50
7.65
625
456
330
241
112
82
b
0.322
8.70
6.80
730
348
415
198
122
58
g
0.374
8.95
8.40
504
417
270
223
98
82
c
0.390
8.85
7.60
493
312
312
197
104
66
i
0.395
9.10
8.60
401
337
262
220
90
76
0.358
(1/1.13)^
551
374
318
216
105
73
IV b
0.400
9.00
8.50
410
345
258
217
94
79
a
0.402
9.10
7.90
473
309
267
175
^5
62
c
0.420
9.00
8.15
451
334
240
178
74
55
i
0.443
9.15
8.40
424
327
227
176
73
56
d
0.459
9.50
7.95
440
258
250
146
77
45
e
0.466
9.30
9.25
355
348
186
182
59
58
0.432
(1/i
loy
426
320
238
179
79
59
Vi
0.501
9,80
9.20
371
307
199
165
69
57
a
0.525
9.65
9.10
362
303
183
154
67
56
b
0.528
9.90
8.60
365
240
205
134
77
51
c
0.534
10.30
8.25
432
222
228
117
78
40
d
0.537
10.00
8.80
412
281
210
143
71
48
e
. 555
9.90
9.00
368
277
164
123
62
47
74
TABLE Z— Continued
BRAIN WEIGHT
CORRECTIONCOEFFICIENT
NUMBER OF CELLS IN A VOLUME OF
- ORTBX, 0.001 MM.'
GROUP
W.D
in fresh brain
W.D
on slide
Lam. pyramid.
Lam. ganglion.
Ganglion cells in
lam. gangl.
Observed
Corrected
Observed
Corrected
Observed
Corrected
,
grams
m m .
mm.
Vf
0.558
10.00
8.55
357
223
182
114
79
49
g
0.564
10.10
9.15
326
242
178
132
62
46
h
0.579
10.10
9.05
318
229
194
140
64
46
0.542
{1/1
i3y
368
258
194
136
70
49
Vic
O.GIO
10.15
8.50
325
190
182
106
65
38
a
0.617
10.55
8.65
322
177
200
110
60
33
e
0.690
10.60
9.40
286
199
191
133
58
40
0.639
(.1/1
19)^
311
189
191
116
61
37
Vila
0.740
11.00
9.20
277
186
149
100
48
32
b
0.760
11.20
8.70
300
140
188
88
47
22
0.750
(1/1
24)'
289
163
169
94
48
27
VIII a
0.800
11.15
8.60
302
138
170
78
43
20
h
0.805
10.60
8.30
293
140
168
80
48
23
b
0.822
11.85
10.20
266
170
138
88
38
24
c
0.849
11.40
9.90
242
158
140
92
37
24
k
0.870
11.45
9.60
257
151
152
90
45
26
d
0.898
11.75
10.20
255
167
138
90
38
25
0.841
(1/1
20y
269
154
151
86
42
24
IX d
0.959
11.80
9.70
241
133
156
86
40
22
e
0.960
12.15
10.10
224
130
147
85
39
23
a
0.972
11.95
9.80
220
122
150
83
41
23
(10 days)
0.964
(1/1. 2iy
228
128
151
85
40
23
Xa
1.033
12.40
10.30
223
128
153
88
45
26
b
1.036
12.40
10.15
212
116
136
75
41
23
e
1.051
12.10
9.40
244
115
149
70
43
20
1.040
(1/1 ■
23y
226
120
142
78
43
23
XI a
1.107
12.90
10.20
234
116
150
74
44
22
b
1.189
13.15
10.30
229
110
148
71
49
24
c
1.193
12.70
10.30
220
118
144
77
42
23
d
1 . 195
12.50
9.80
222
107
142"
68
44
21
(20 days)
1.171
(1/1.
26)^
226
lis
146
73
45
23
XII c
1.234
12.95
10.70
210
118
136
76
48
27
a
1.273
12.90
9.10
248
■ 87
171
60
55
19
1.253
(1/1. 3iy 1
229
103
154
68
52
23
TABLE 3— Concluded
BRAIN
WEIGHT
CORRECTIONCOEFFICIENT
NU.MBER
OF CELLS
IN .V VOLUME OF CORTE.X, 0.001 MM. 3
GROUP
W.D
in fresh brain
W. D
on slide
Lam. pyramid.
Lam. ga
nglion.
Ganglion cells in
lam. gangl.
Observed
Corrected
Observed
Corrected
Observed
Corrected
grams
m in .
m m .
XIII a
1.301
13.20
10.25
212
99
177
83
56
26
g
1.307
12.70
10.00
205
100
163
80
52
25
b
1.327
13.35
9.70
243
94
180
69
60
23
c
1.346
13.15
9.85
218
92
174
73
57
24
h
1.392
13.10
10.90
190
110
140
81
50
29
1.335
(1/i
29)3
214
99
167
77
55
25
XIV a
1.412
13.65
10.30
212
91
164
71
58
25
e
1.441
13.10
9.20
248
86
176
61
63
22
b
1.483
13.80
10.80
218
105
172
82
60
29
1.U5
U/1
■ 34)'
226
94
171
71
60
25
XV a
1.530
13.80
10.80
185
88
134
64
47
23
b
1.542
13.70
10.40
207
90
144
63
49
22
c
1.552
13.50
10.30
183
81
152
67
52
23
d
1.573
13.90
10.60
184
82
130
58
53
24
e
1.574
13.70
10.50
204
93
134
60
52
23
1.55i
(1/1
.30)3
193
87
139
62
51
23
XVI a
1.642
13.80
11.20
170
91
127
68
50
27
g
1.643
13.40
9.50
225
81
148
53
56
20
c
1.647
14.00
10.50
186
79
134
57
55
23
e
1.690
13.45
10.00
207
84
148
61
63
26
1.656
(1/1.33)3
1
197
84
139
60
56
24
XVII f
1.720
13.50
9.60
208
75
151
54
60
22
a
1.721
14.00
11.00
178
86
132
64
55
27
b
1.730.
14.70
12.35
142
84
118
70
44
26
c
1.731
14.40
12.10
144
85
106
63
42
25
1.726
(1/1
.26)3
16%
83
127
63
50
25
XVIII c
1.817
14.00
10.10
188
71
142
53
54
20
a
1.844
15.00
12.10
170
89
126
66
48
25
e
1.855
14.30
10.60
192
78
139
57
60
24
1.839
(.1/1
.32)3
183
79
136
59
54
23
XIX a
1.924
14.10
10.90
174
81
110
51
52
24
1.924
(1/1
.29)3
174
81
110
51
52
24
XX a
2.039
14.80
12.10
150
82
95
52
38
27
b
2.069
14.60
11.70
151
78
96
49
37
19
2.054
(i/i.23y'
151
80
96
51
38
20
76
GROWTH OF THE CEREBRAL CORTEX 77
As already shown (Sugita, '17, '17 a), the longitudinal diameter of the sagittal section (from the frontal pole to the occipital pole), that is L. F, as well as the cortical thickness, are both steadily increasing as the brain weight increases. The thickness of the cortex is one component of its area in the section, the other being obtained by dividing the area by the thickness, and the length thus found is correlated with the longitudinal diameter of the section (L. F) as defined above. The increase of the cortical area will therefore depend on the increase in cortical thickness and the increase in the longitudinal diameter of the section (L. F). Table 4 shows these relations. Column B gives the average brain weight by groups, column C the average corrected area of the cortex (taken from table 1), column D the cortical thickness (Tg) and column F the diameter L. F, all in the fresh condition of the brain and the last two quoted from the data already pubHshed (Sugita, '17, '17 a). In column E is given the ratio C/D or the computed length of the long side, when the cortical area is reduced to a rectangle with the short side equal to the cortical thickness. If these computed lengths are compared with the actual longitudinal diameters of the cerebrum (L. F), given in column F, it is of interest to note that, in brains weighing more than 0.5 gram, the ratios, given in column G as E/F, are quite similar, ranging between 1.16 and 1.25 (average 1.22).i In the newborn or before birth (Group I), the ratio is somewhat higher. So, if necessary, the cortical area in the* sagittal sections may be obtained by the following formula
L.F X T^X 1.22 (L. F and T„ in millimeters)
As the. sagittal cortical thickness in brains weighing more than 1.17 grams increases only slowly, the cortical area in the sagittal section in brains older than twenty days is approximately proportional to the longitudinal diameter of the cerebrum (L. F).
E. The area of the cortex in the frontal section
Reviewing table 2 and chart 1 (graph f), we see that the cortical area in the frontal section increases in the same manner
1 In making comparisons with the Norway rat in part II of this paper, the average ratio given by Groups XIII to XX will be that used. This average is 1.21.
THE JOURNAL OP COMPARATIVE NEUROLOGY, VOL. 29, NO. 2
78
NAOKI SUGITA
TABLE 4
Showing the relations of the cortical area in the sagittal section to the longitudinal diameter (L. F) of the cerebrum and the cortical thickness. All values for the fresh condition. Albino rat.
A
B
c
D
E
F
G
GBOTTP
BRAIN
WEIGHT
CORTICAL
AREA
IN SAGITTAJ.,
SECTION
CORTJCAL
THICKNESS
IN SAGITTAL SECTION
c
D
L.F
IN FflESH BRAIN
E
F
grams
m m .
mm.
mm.
mm.
r
0.161
AA
0.52
8.5
5.6
1.52
II (birth)
0.251
5.8
0.67
8.7
6.4
1.36
III
0.358
8.3
0.90
9.2
7.4
1.24
IV
0.432
10.1
0.99
10.2
8.0
1.27
V
0.542
12.6
1.14
11.0
8.9
1.24
VI
0.639
15.5
1.29
12.0
9.6
1.25
VII
0.750
18.1
1.43
12.7
10.4
1.22
VIII
0.841
20.1
1.48
13.6
11.0
1.24
IX (10 days)
0.964
21.7
1.55
14.0
11.6
1.21
X
1.040
23.5
1.59
14.8
12.0
1.23
XI (20 days)
1.171
26.6
1.72
15.5
12.5
1.24
XII
1.253
26.1
1.75
14.9
12.8
1.16
XIII
1.335
27.6
1.72
16.0
13.0
1.23
XIV
1.445
28.2
1.70
16.6
13.3
1.25
XV
1.554
28.7
1.76
16.3
13.7
1.19
XVI
1.656
29.2
1.77
16.5
14.1
1.17
XVII
1.726
31.1
1.79
17.4
14.3
1.22
XVIII
1.839
32.8
1.86
17.6
14.7
1.20
XIX
1.924
32.3
1.80
17.9
15.0
1.19
XX
2.054
33.7
1.80
18.7
15.3
1.22
Average (Groups V
-XX)
1.22
Average (Groups X
III-XX) .
1.21
as in the sagittal section though more slowly. The cortical area in the frontal section is a product of the cortical thickness (7",,) and the length of the cortex along the cerebral surface. This surface line of the cortex in the frontal section may be regarded as a part of a circle and its length may be taken as proportional to the length of the radius or the measurement W. D (the frontal diameter of the cerebrum), which was measured across the section horizontally (Sugita, '17). As shown in table 5,
GROWTH OF THE CEREBRAL CORTEX 79
which is comparable with table 4, the relative value C/D or
-, — and the ratio of this value to W. D were
Cortical thickness
calculated. The ratio, given in column G, table 5, falls between
0.85 and 0.99 (average 0.91)^ in brains weighing more than 0.5
gram, but shows a tendency to gradually increase as the brain
weight increases. In the newborn or before birth (Group I)
it is somewhat higher. If the average ratio be taken as usable
for all groups, as in the case of the sagittal section, the cortical
area in the frontal section may be approximately obtained by
the following formula:
If. D X T^ XO.91 (W. D and T^, in millimeters)
As, in brains weighing more than 0.95 gram, the cortical thickness in the frontal section (Tp) varies only slightly, the cortical area in the frontal section in these brains will be practically proportional to the frontal diameter of the cerebrum {W. D). The agreement of the calculated with the observed values is however not so good as in the case of the sagittal section.
F. The area of the entire frontal section
In chart 1, the graph F, representing the total area of the frontal section, is accompanied by a dotted line T, which represents the value of the square of the cube root of the brain weight (in grams). Theoretically, under the assumption that the specific gravity of the brain remains the same throughout the life, the latter should run a similar course to the former, if the brain enlarges proportionally in all dimensions as it grows. Between Groups II to XIV, both curves take nearly the same course, if some slight discrepancies in the observed values are neglected. But in brains weighing more than 1.4 grams, the differences become so distinct, that they can no longer be regarded as due to errors in measurement. This is probably due to the fact that the brain is not enlarging proportionally in all diameters,
- In making comparisons with the Norway rat in part II of this paper, the average ratio given by Groups XIII to XX will be that used. This average is 0.93.
80
NAOKI SUGITA
TABLE 5
Showing, in columns A to E, the relations of the cortical area in the frontal section to the frontal diameter of the cerebrum iW . D) and the cortical thickness, and, in columns H to J, the relations of the total area of the frontal section and the frontal diameter of the cerebrum. All values for the fresh condition. Albino rat.
A
B
c
D
E
F
G
H
I
J
GROUP
BRAIN
WEIGHT
CORTICAL
AREA
INFRONTAL SECTION
CORTICAL
THICKNESS INFRONTAL
SECTION
D
W. D
IN
FRESH MRAIN
E
F
TOTAL
AREA
OF FRONTAL SECTION
SQUARE
OF
W. D
gra7ns
irim.'^
m m .
mm.
m m .
mm.^
7)1 m."
I
0.161
3.9
0.56
7.0
6.6
1.06
11.9
43.6
0.27
Ilfbirth)
0.251
5.7
0.78
7.3
7.7
0.95
17.0
59.3
0.29
III
0.358
8.0
1.02
7.9
8.7
0.91
20.6
75.7
0.27
IV
0.432
9.1
1.11
8.2
9.3
0.88
22.4
86.5
0.26
V
0.542
11.7
1.33
8.7
10.1
0.86
26.9
102.0
0.26
VI
0.639
14.4
1.55
9.3
10.6
0.88
31.1
112.4
0.28
VII
0.750
16.4
1.74
9.5
11.2
0.85
32.6
125.4
0.26
VIII
0.841
18,4
1.82
10.1
11.6
0.87
38.9
134.6
0.29
IX (10 days)
0.964
20.4
1.86
11.0
12.1
0.91
42.3
146.4
0.28
X
1.040
20.8
1.82
11.4
12.4
0.92
44.2
153.8
0.29
XI (20 days)
1.171
21.7
1.91
11.4
12.7
0.90
45.7
161.3
0.28
XII
1.253
23.0
1.91
12.0
13.0
0.92
47.2
169.0
0.28
XIII
1.335
23.2
1.94
12.0
13.2
0.91
50.2
174.2
0.29
XIV
1.445
24.8
1.99
12.5
13.4
0.93
52.3
179.6
0.29
XV
1.554
24.3
1.97
12.3
13.5
0.91
54.0
182.3
0.30
XVI
1.656
24.3
1.94
12.5
13.7
0.91
54.9
187.7
0.29
XVII
1.726
24.6
1.90
12.9
13.8
0.94
56.4
190.4
0.30
XVIII
1.839
26.0
1.97
13.2
14.1
0.94
58.9
198.8
0.30
XIX
1.924
24.8
1.83
13.5
14.3
0.94
57.0
204.5
0.28
XX
2.054
24.9
1.72
14.5
14.6
0.99
63.4
213.2
0.30
Average (Groups
^-XX)
0.91
0.28
Average (Groups ]
^111-5
- x) . . . .
0.93
the increase in the frontal diameter being retarded relative to the sagittal diameter in brains weighing more than 1.4 grams (Sugita, '17).
If, as given in columns H and I, table 5, the area of the total frontal section is compared with the square of W. D of the corresponding brain group, the above inference will be supported by the fact that the ratio, given in column J of the same table,
GROWTH OF THE CEREBRAL CORTEX 81
is almost equal throughout all brain weight groups, swinging within the narrow limits of 0.26 to 0.30.
G. Percentage of the area of cortex in the total area of the frontal section (one hemicerehrum)
Figure 2 shows the outline of the frontal section. In the section we see as the principal divisions the cortex, the striatum, the thalamus, the capsula externa and the lateral ventricle, and, among these, the cortex and the striatum stand in marked contrast. In the young brains, the lateral ventricle is wide. This cavity was not included in the measurement of the area. In the wall of it, especially at the dorso-lateral corner, there are seen masses of dividing cells and of neuroblasts, which are due to migrate into the cortex. But in the older brains weighing more than 1.1 grams, the ventricular wall is almost free from dividing cells and the cortex is no longer receiving new cells. By determining the percentage of the cortical area to the total area of the frontal section, we may obtain some clue as to mass relation of the cortex to the other structures seen in the frontal section.
As previously given in table 2, the cortical area in the frontal section amounts to 34 per cent of the total area at birth. It increases from birth up to bi'ains weighing 0.7 to 1.2 grams, when the percentage reaches its highest figure, that is, 50 or sometimes 51, on the average 48 per cent. After this stage, the percentage slowly diminishes as the brain weight increases, and, at full maturity, it reaches 44 per cent or less; even 39 per cent in an old brain weighing more than 2.0 grams. This means clearly that the cortical area increases rapidly by receiving new cells from the matrix and at the same time by the enlargement and separation of the cell bodies, during the first phase, covering the first ten days after birth.
In this phase, as a matter of fact, the remainder of the section is for the most part composed of the matrix and migrating cells, the central nuclei being not yet so largely developed. The transitional layers, or the areas previously occupied by the
OZ NAOKI SUGITA
transitional layers, which will be replaced by the capsula externa, are relatively wide during this phase.
After twenty daj^s, when the brain has attained nearly the weight of 1.17 grams, the remainder of the section (the central nuclei and the white substance) increases more rapidly than the cortical area and the group of proliferating cells in the ventricular wall disappears. The percentage of the cortical area to that of the whole section consequently decreases under these conditions, though the absolute value of the cortical area is steadily increasing.
From the mode of the changes in the percentage value of the cortical area, we may conclude that, in the albino rat, at least, the period during which the brain weight increases from 0.25 gram (birth) to 1.2 grams (about 20 daj^s), is the period when the cortical elements are principally produced, matured and arranged, and that the cortex is precocious in its construction. The growth or construction of the remaining parts in the frontal section, so far at least as this is expressed by increase in volume, is relatively retarded or delayed until the cortex has acquired all its characteristic elements.
H. The volume of the entire cortex
The true volume of the entire cerebral cortex can not be measured by the methods here used. It will require a special study for that purpose. My present object is to obtain relative values for the cortical volume and a record of the change in these relative values according to brain growth. If the data for the area of the cerebral cortex as measured by me in the two typical sections be reduced to a simple geometrical form, it will be very easy to compare the changes in the computed volume in successive brain weight groups. As already mentioned, the cortical area in the sagittal and the frontal sections, which sections cross one another at right angles, may be reduced to rectangles which have as the long side the lengths proportional respectively to the sagittal and the frontal diameters of the cerebrum (L. F and W. D), and as the short side the cortical
GROWTH OF THE CEREBRAL CORTEX
83
thicknesses {T^ and Tp). For the present purpose, the mean cortical thickness (T) may be substituted for both the foregoing values of the cortical thickness, when the brain weight is the same, because T falls at the mean of the T^ and T^, so that the gain in T^ would be compensated by the loss in T^ (fig. 3). As a consequence the volume of the cortex may be represented by an index value, the formula for which follows.^
L.FX W. D XT
(all in millimeters)
CKNES5 OF CORTEX
Fig. 3 The solid lines show the simplified geometrical form used to indicate the volume of the entire cortex, which is assumed to be proportional to the rectangular form designated by dotted lines in the figure. The volume of the rectangular figure, which was obtained by the value: L. F y, W . F X T, has been tabulated in column F, table 6, and plotted as graph LWT in chart 2.
The values thus obtained — which mean the actual volume of the rectangle denoted by dotted lines in figure 3 — stand in a fixed relation to the true cortical volume which is denoted by solid lines in the same figure, as far as the latter retains a similar form during growth.
5 In this formula, the coefficients 1.22 and 0.91, which were empirically determined, were eliminated, because these coefficients are fixed throughout all the groups to be compared. For Groups XIII to XX, the coefficients are respectively 1.21 and 0.93, and these will be taken into consideration when comparison is made between the Albino and the Norway rats.
8-i
NAOKI SUGITA
TABLE 6
Giving for each brain weight group the average brain weight, ratio in cerebral volume, computed cortical volume and the data used to obtain the computed cortical volume, and ratio in cortical volume
A
B
C
D
E
F
G
BRAIN WEIGHT GROUP
BRAIN
WEIGHT
RATIO
OF
VOLUME
OF
CEREBRUM
L.F
IN FRESH BRAIN
W. D
IN FRESH BRAIN
AVERAGE
CORTICAL
THICKNESS
L. FX
W. DXT,
COMPUTED VOLUME
OF CORTEX
RATIO OF
COMPUTED
VOLUME
OF COKTEX
grams
m m .
m m .
m m .
?n»i.'
I
0.161
5.6
6.6
0.54
19.96
II (birth)
0.251
1.00
6.4
7.7
0.73
35.97
1.00
III
0.358
1.34
7.4
8.7
0.96
61.81
1.72
IV
0.432
1.66
8.0
9.3
1.10
81.84
2.28
V
0.542
2.12
8.9
10.1
1.24
111.46
3.10
VI
0.639
2.53
9.6
10.6
1.42
144.50
4.02
VII
0.750
3.12
10.4
11.2
1.58
184.04
5.12
vni
0.841
3.50 '~
11.0
11.6
1.65
210.54
5.85
IX (10 days)
0.964
4.04
11.6
12.1
1.71
240.02
6.67
X
1.040
4.10
12.0
12.4
1.72
255.94
7.12
XI (20 days)
1.171
4.61
12.5
12.7
1.82
288.93
8.03
XII
1.253
4.80
12.8
13.0
1.8S
304.51
8.47
XIII
1.335
5.17
13.0
13.2
1.83
314.03
8.73
XIV
1.445
5.40
13.3
13.4
1.85
329.71
9.17
XV
1.554
5.89
13.7
13.5
1.87
345.86
9.62
XVI
1.656
6.05
14.1
13.7
1.86
359.30
9.99
XVII
1.726
6.44
14.3
13.8
1.85
365.08
10.15
XVIII
1.839
6.72
14.7
14.1
1.92
397.96
11.06
XIX
1.924
6.91
15.0
14.3
1.82
390.39
10.85
XX
2.054
7.85
15.3
14.6
1.76
393.15
10.93
1 T, here entered, is the mean value of Ts and T^, previously given in tables 4 and 5 and is not the general average thickness of the cortex of the sagittal, frontal add horizontal sections formerly presented in my second paper in this series (Sugita, '17 a) .
Table 6 shows the values for the cortical volume computed by the above method and the ratios, the cortical volume at birth being taken as the unit of the comparison.
Chart 2 (graph LWT) shows graphically the ratios obtained (table 6, column G), accompanied by the graph (graph LWH) which shows the increase in volume of the cerebrum (table 6, column B). The volume of the cerebrum was computed according to my previous procedure (Sugita, '17). From this
GROWTH OF THE CEREBRAL CORTEX
86
chart we see that the cortical volume increases more rapidly than the entire cerebral volume, until the brain attains the weight of 1.17 grams (20 days) (see crosses in chart 2), If we take these marks as the starting points, then the cerebral volume increases to about 1.7 times at full maturity and in the same way the cortical volume increases to about 1.4 times compared with the value at twenty days (table 6). So, it may be stated that after twenty days the increase in cortical volume becomes
^2
n
10 9
X
y—
~-«v,_
-:^
'°N.
■ L\A
T
-^
y^"
-■
^^
"~tf'
^'^
"^s^
"°"
■
■Tiu
VT°
_^-'
x^
^•^
-^^
6
\
/
/'"
y
/
^'^
f
6
5
4
-^
A
y
y
,,,
'-"
•'■
/
\
\
/
/•'
,..„
'-
'
\
\
/
/
,
'-'■'
"■"
>
\
__,
,-'
'
/
^'
V
^-^
~^.-_
^
— »—
-" —
-.-_
'
N
^
^
0.1 0.2 B 0.3 0.4 05 0.6 0.7
09 10 11 12 13 14- 15 ife i? 18 19 2.0 Jmi
Chart 2 Showing the ratios of the values for the cortical volume, the volume of the cerebrum, the cell density in two unit volumes and the computed number of nerve cells in the entire cerebral cortex of the albino rat, according to the
brain weight. • • LWT, The ratios of the computed volume of the cerebral
cortex, the volume at birth being taken as the unit. Based on the data in table
6. . • LWH, The ratios of the volume of the entire cerebrum,
the volume at birth being taken as the unit. Based on the data presented in a former paper (Sugita, '17) and given also in table 6. X XN, The cell density in two unit volumes of the cortex. Based on the data given in column C, table 7, as N", and plotted here according to the values corresponding to one onehundredth of the number given in column C, table 7. •■ — •" * NLWT, The ratios of the computed number of nerve ce»lls in the entire cortex, the value at birth being taken as the unit. Here the unit chosen on the ordinate is 5. The data are given in column E, table 7.
86 NAOKI SUGITA
slower and is somewhat less in rate than the increase in cerebral volume or brain weight, as is also seen in the graphs given in chart 2.
/. Number of cells in a unit volume of the cortex
In the lamina pyramidalis of the newborn Albino brain, at a dorso-lateral part of the pallium, where, in the frontal section, the cell count was irfade (fig. 2, VII), there were in the fresh condition about 500 pyramids crowded in a unit volume of 0.001 mm.^' This number decreases, as the brain grows, and falls to 110 in a brain weighing about 1.2 grams (20 days) (table 3). In a brain weighing about 1.5 grams (50 days), the number has dropped nearly to 90, from which it is only slightly reduced in the heavier brains. In an old rat, whose brain weighs more than 2.0 grams, the number is about 80, or less than one-sixth the number at birth. According to another study, which will be published later, the size of the cell body and of the nucleus of the pyramids in the lamina pyramidalis, measured at this same locality, increases very rapidly during the first ten days after birth, till the brain has attained 0.9 gram in weight, when these structures reach their maximum size (Cell body 16/x X 20ju; Nucleus 14;u X 15m). After this stage the cell body and the nucleus ar'e mature in their nucleus-plasma relation, but still changing their chemical composition, as revealed by the stains, while the neuron as a whole is still growing as shown by the developing axon and the dendrites.' This fact is in accord with the observation that the number of pyramidal cells in the lamina pyramidalis decreases rapidly after birth, until the brain weight reaches about 0.9 gram (10 days), after which the rate of decrease becomes slow.
The change in cell number in a given volume of the cortex during the growth of the brain is determined by two main factors: (1) the enlargement of the cell body proper and the growth of the cell branches and (2) the development of the intercellular structures (that is, incoming nerve fibers, neuroglia, blood vessels) and myelin formation, separating the cells more and more from each other.
GROWTH OF THE CEREBRAL CORTEX 87
As to the cells in the lamina ganglionaris, the relation is somewhat different from that just described. The total number of cells, including both the small and large pyramids, decreases relatively rapidly after birth, until the brain weight reaches 1.25 grams (25 days). It then shows a slight increase (table 3, Groups XIII and XIV), but decreases again by slow steps and remains almost fixed after 35 days (brain weight 1.4 grams) at 60. Finally, in old rats, only 50 cells were counted in a unit volume of 0.001 mm. ,3 or about one-fifth the number at birth.
If the number of the large pyramids alone is considered, then the number decreases rapidly from birth to a brain weight of 0.8 gram (9 days). After this, it decreases slightly and remains almost fixed at 23 up to a brain w^eighing 1.2 grams. In brains weighing 1.3 to 1.5 grams it shows a tendency to increase slightly for a time — corresponding to the increase in total number of cells in this layer (above mentioned) — but finally becomes fixed again at 23 to 24 throughout maturity. In old age, it has diminished to 20 or about two-sevenths the number at birth. The large ganglion cells attain nearly their full size (Cell bod}^ 21^ X 28m; Nucleus 18m X 19m) at 0.9 gram in brain weight (10 days), almost at the same time as the small pyramids.
I can not, from the data at hand, satisfactorily explain the increase in cell number in the lamina ganglionaris in the period during which the brain grows from 1.2 grams to 1.4 grams in weight. This fact might however have some connection with the chemical structure of the cells and consequently be related to a change in reaction to the reagents used, so that the size of the large pyramids, after having attained a maximum (21m X 28m) at a brain weight of 0.9 gram, diminishes slightl}^ at the same time that their response to the stain changes somewhat, measuring only 20m X 27m at a brain weight of 1.3 to 1.4 grams, after which they again enlarge to a full size of the cell body (sometimes over 23m X 30m). In the carbol-thionine staining the sections from brains weighing less than 1.0 gram show a violet tone, those from brains weighing more than 1.2 grams a blue tone while those from brains weighing 1.0 to 1.2 grams are intermediate in tone. We shall pass over this question now,
88 NAOKl SUGITA
as a detailed description of the size of each cell type and its mode of enlargement according to age will be the theme of a later paper.
To represent the relative cell density in the cerebral cortex for each brain weight group, the sum of the cell numbers in the lamina pyramidalis and the lamina ganglionaris, given in table 3, was used, in order to balance, in some measure, the inequality of the cell distribution. These values are given in table 7, column C, and in chart 2 (graph N). Both table and chart show that the number of nerve cells in a unit volume of the cortex decreases verj^ rapidly during the first ten days after birth (up to the brain weight of 0.95 gram) and after that time it decreases slowly but steadily as the age advances. The cell number at maturity is nearly one-fifth the value at birth.
J . Values for the co7nputed yiumher of nerve cells in the entire cerebral cortex, according to brain weight
The number of nerve cells given in table 3 does not means the actual volume of complete cells contained in a unit volume, because the parts of cells which showed a nucleus but no nucleolus in the section were also counted. In spite of this, the number in the table indicates fairly the relative number of cells or the relative cell density at different ages in the localities examined, and from this we may be able to get some indication as to the number of nerve cells in the entire cerebral cortex.
If the actual number of cells in a unit volume be proportional to the number of cells counted, the number of cells in the entire cerebral cortex may be indicated (theoretically) by this number multiplied by the number obtained by dividing the volume of the entire cerebral cortex by the unit volume.
The actual volume of the cortex was not measured, but the computed volume is indicated by the following formula, as explained already.
L.F XW.D XT (all in millimeters)
So, if N means the cell number in a unit volume (for example,
GROWTH OF THE CEREBRAL CORTEX 89
N is 240 for Group VIII, as shown in table 7, column C), the relative value of the number of nerve cells in the entire cortex may be computed by the following formula.^
NxL.FxW.DxT (L.F, W.D and T, in millimeters)
The results of this computation are shown in table 7 and in chart- 2 (graph NLWT), where the necessary data were all taken from the present or former papers and the relative value of N X L. F X W. D X T is calculated. For N, the corrected sum of the cell numbers in the lamina pyramidalis and in the lamina ganglionaris, given in table 3, was used (table 7, column C). The results are quite interesting. As seen from table 7, columns D and E, and chart 2 (graph NLWT based on column E,), the relative value of the computed number of cells in the entire cortex increases rapidly from birth to a brain weighing 0.9 gram (about 10 days), and then for a while the increase becomes slow up to a brain weight of 1.17 grams (20 days), attaining at this time nearly the complete number of nerve cells (see graph NLWT, mark X in chart 2) . After having passed this phase, the value for the number of cells remains almost constant throughout the life. The average of the values for Groups XI-XX in table 7 is 530, so that between birth and maturity the number of cells counted has increased two times, but nearly al^ of this increase has taken place during the first ten days of life. These results coincide v.ery well with the conclusions of Allen ('12), that in the cerebrum mitosis continues with diminishing activity to the 20th day after birth.
'^ By this computation the number of cells in the entire cortex will be equal to the number of times the unit of volume, 0.001 mm.' in which the cells were counted, is contained in the entire volume of the cortex, multiplied by the number of cells in a unit volume. The number of cells designated by N is however the sum of the numbers in two unit volumes, that is, the number in one unit volume of the lamina pyramidalis plus the number in one unit volume of the lamina ganglionaris.
Since the numbers of cells used, N, is that in two unit volumes, the foregoing product must be divided by two. As dividing the volume of the cortex by 0.001 is equivalent to multiplying it by 1000, and as the product must be divided by two, the operation may be expressed as follows:
N X L. F X W. D X T X oOO = Number of cells
90
NAOKI SUGITA
TABLE 7
Giving the computed number of nerve cells in the entire cerebral cortex, obtained on the basis of the measurements given in this series of studies. The ratio of the mimber of cells of each later group to that of Group 11 (birth) is also given
A
B
C
D
E
COMPUTED
BRAI.V WEIGHT GROUP
BRAIX
WEIGHT
COMPUTED
VOLUME OF
CORTEX
L.FX ir. D X T
SUM OF XOS.
OF CELLS I.V
L.\M. PYR. AXD
■LAM. GAXG.
IX TWO UNIT
NUMBER OF
CELLS IN CORTEX,'
A XL.FX W. D XT
RATIO
OF NU.MBER
OF CELLS
VOLUMES, K
^ 100
gra m s
mrn.^
II fbirthi
0.251
35.97
739
265.8
1.00
III
0.358
61.81
590
364.7
1.37
IV
0.432
81.84
499
408.4
1.54
^'
0.542
111.46
394
439.2
1.65
VI
0.639
144.50
305
440.8
1.66
VII
0.750
184.04
257
473.0
1.78
VIII
0.841
210.54
240
505.3
1.90
IX flO days)
0.964
240.02
213
511.2
1.92
X
1.040
255.91
198
506.8
1.91
XI (20 davs)
1.171
288.93
186
537.4
2.02
XII
1.253
304.51
171
520.7
1.96
XIII
1.335
314.03
176
552.7
2.08
XIV
1.445
329.71
165
544.0
2.05
XV
1,554
345.86
149
515.3
1.94
XVI
1.656
359.30
144
517.4
1.95
XVII
1.726
365.08
146
533.0
2.01
XVIII
1.839
397.96
138
549.2
2.07
XIX
1.924
390.39
132
515.3
1.94
XX
2.854
393.15
131
515.0
1.94
Average (Groups !X
- i-xx) ....
530.0
2.00
Average (Groups ^
- iii-xx) ..
530.2
2.00
1 As explained in a footnote (footnote 4j, the actual number of cells contained in the computed volume of the cortex should be N X L. F X W. D X T X 500, but, for the convenience, 1/100 of N X L. F X W. D X T, or 1/50,000 of the actual numbet of cells contained in the computed volume, was given here as the computed number of cells in the cortex.
The above statement that between birth and maturity the nmnber of nerve cells in the entire cortex has increased twofold, does not necessarily mean that the additional cells have been all newly formed after birth. As a matter of fact, we see,
GROWTH OF THE CEREBRAL CORTEX 91
in the sections of the newborn brains, many immature cells, the indifferent cells and the neuroblasts, crowded densely together in the ventricular wall and in the transitional layers and these are all migrating to the cortex. The number of cells in the cortex is increased after birth by receiving these cells already formed but lying at birth still outside of the cortex proper, besides by receiving the cells which are newly formed after birth. So the nerve cells, destined for the cortex, are largely present in immature form in the cerebrum at birth, but lie outside of the cortex proper, while the actual number of cells formed after birth may amount only to a small fraction of the total number of nerve cells in the cortex at maturity, though there is active mitosis during the first days after birth.
I have previously recognized three developmental phases in the growth of the cortex in thickness (Sugita, '17a), as f ollow^s :
First phase, from birth to the 10th day.
Second phase, from the 10th to the 20th day.
Third phase, from the 20th to the 90th day.
The first and the second phases here given may also be applied, without any modification, to the changes in cell number in the cerebral cortex, while the third phase does not appear in this connection.
IV. CONCLUSIONS
In an earlier study on the cerebral cortex of the albino rat (Sugita, '17 a), I stated that the cerebral cortex attains nearly its full thickness at the age of twenty days, before myelination in the cortex had begun, and that the organization of the cerebral cortex might be considered as precocious, having been provided with all its mechanisms at the time of weaning. At this age, the brain weight is only a little more than one-half the weight at maturity. Size, volume and weight of the entire brain are^ all midway in their growth, but there have appeared no striking changes by which we might guess from the gross appearance of the brain anything about the numerical completeness of its cortical elements. Just at this stage, however, cell division in the cerebrum has almost ceased (Allen, '12).
92 NAOKI SUGITA
From the data now available, I conclude that, in the albino rat, the cerebral cortex exhibits the complete number of nerve cells at about the 20th day after birth, at which age some of the cells have attained their full size. The area of the cortex in the sagittal and in the frontal sections has shown a continuous increase throughout life and no radical change in rate occurs at this time. But, if the thickness of the cortex be taken into consideration and the volume of the entire cortex be calculated, it becomes clear that the entire volume of the cerebral cortex has stopped the more active increase, which it made earlier, at about the 20th day, and after that the increase becomes slow, and lower in rate than the increase in the volume of the cerebrum. If, further, the' cell density in the cortex be considered, it is found that the number of cells as computed for the cerebral cortex (table 7, column E) increases rapidly, especially during the first ten days after birth, but exhibits nearly its complete number at the age of twenty daj^s, after which it shows no significant change.
We may conclude therefore that the cerebral cortex has been completely organized at the age of about twenty days, and that the further development of the cortex does not involve an increase in cell number, but involves mainly the maturing of elements already provided. The education of the cerebral cortex as a whole might properly be said to begin after this age, the preceding period having been largely one of preparation or construction. It is of interest to note that this epoch corresponds to the weaning time of the rat.
According to the study of Donaldson ('08) on the comparison of the albino rat and man, the rat grows thirty times as fast as man. When however the brain of the rat is to be compared with that of man, it must be remembered that at birth the human brain is somewhat more mature and corresponds in organization not with the rat brain at birth but at five days of age (Donaldson MS.). This being the case, the rat cortex at the 20th day of postnatal life probably corresponds with the human cortex at the 15th month (20 less 5). This conclusion has not yet been tested.
V. SUMMARY
1. Empl-oying the sagittal and the frontal sections of 78 albino rats, which were formerly used for the investigation on the thickness of the cerebral cortex (Sugita, '17 a), I made further measurements on the area of the cortex in these sections and counted at a fixed locality the number of nerve cells contained in a unit volume of 0.001 mm,,^ in brains from birth to maturity.
2. The observed data were all corrected to the values for the fresh condition of the material, by the use of the correctioncoefficients based on the observations. The results were grouped and averaged according to the brain weight groups and the postnatal growth changes systematically analysed.
3. The area of the cortex shown in the sagittal section is found to be proportional to the value L. F X T^, where L. F is the longitudinal diameter of the cerebrum and T^ is the average thickness of the cerebral cortex in the sagittal section. The actual area (after five days of age) may be calculated by the formula: L. F X T^ X 1.22 (L. F and T^, in millimeters), where 1.22 is a constant coefficient which was empirically determined (see table 4, column G).
4. The area of the cortex shown in the frontal section (of one hemicerebrum) is found to be proportional to the value W.D X T^, where W. D is the frontal diameter of the cerebrum and T^ is the average thickness of the cortex in the frontal section. The actual area (after five days of age) may be calculated by the formula: W.D xT^ X 0.91 {W.D and T^, in millimeters), where 0.91 is a constant coefficient which was empirically determined (table 5, column G).
5. The percentage of the total' area of that frontal section which is represented by the cortical area is least at birth (34 per cent) and increases as the age advances till it reaches the maximum (50 per cent) at the period of 7 to 20 days (brain weight 0.75 to 1.25 grams). It then decreases, slowly and at maturity is less than 44 per cent (table 2). This means that durihg the first 7 days the cortex is increasing in area more rapidly than the remainder of the section, while during the
following 13 days its rate of increase is similar to that of the remainder. After 20 days the rate of increase for the remainder
surpasses that for the cortex.
6. The actual volume of the cortex could not be obtained by the use of the data now available, but the cornputed volumes of the cerebral cortex at different ages (comparable among themselves), may be found by the use of the formula: L. F X W.D xT (all in millimeters), where L. F is the longitudinal diameter of the cerebrum, W. D is the frontal diameter of the cerebrum and T is the average thickness of the cortex. The volume increases most rapidly during the first ten days after birth and the rate of increase in the cortical volume continues to surpass the rate of increase in the entire cerebral volume, during the first twenty days. After twenty days the cortex increases at a somewhat lower rate than the increase of the entire cerebrum in volume (chart 2).
7. The number of cells contained in a unit volume of 0.001 mm.-^ of the cortex indicates the cell density of the locality where the count was made. In the lamina pyramidalis the pyramids are most crowded at birth and the number in the unit volume decreases rapidly during the first ten days after birth. After twenty days it decreases slowly but steadily, the number at maturity being about one-sixth the number at birth. As for the lamina ganglionaris, the total cell number in the unit volume (the small and the large pyramids taken together), is at its highest value at birth. It decreases relatively rapidly during the first twenty-five days after birth, then is slightly increased for a time, after which it decreases again slowly and at full maturity it shows about one-fifth the number present at birth. Taking the large ganglion cells alone, we find that the number decreases rapidly during the first eight to ten days, then remains the same up to twenty days, after which it decreases again, showing two-sevenths the initial number at full maturity. The decrease in cell density according to brain growth is due to the enlargement of cell bodies, the deA'elopment of cell attachments, the separation of cells from each other through myelination, ingrowing fibers and other changes. The average cell density,
represented by the sum of the numbers in the lamina pyramidalis and the lamina gariglionaris, given as A^ in table 7, decreases rapidly during the first ten days and after that the decrease becomes very slow and steady, showing at maturity a
density of about one-fifth of that at birth.
8. The computed value for the number of cells in the entire cerebral cortex may be determined by the formula: N X L. F X W.D X T {L.F, W.D and T, all in millimeters), where L. F is the longitudinal diameter of the cerebrum, W. D the frontal diameter of the cerebrum, T the average thickness of the sagittal and frontal cortex and A^ the average number of the nerve cells in two unit volumes of the cortex, at the particular locality (locality VII) where the counts were made. This computed value for the number of nerve cells in the entire cerebral cortex increases rapidly during the first ten days, at the end of which period it attains nearly 1.9 times the value at birth. During the following ten days, it increases slowly but steadily, and it attains its complete number at the age of twenty days (brain weight 1.17 grams). After this age the number of nerve cells is almost constant. The number of cells at maturity is twice the number at birth.
It is recognized that this conclusion concerning the number of nerve cells in the cortex at various ages is based on enumerations in only two cortical layers at but one locality, and that on this ground its general value might be questioned. When it is recalled however that table 11 in a preceding study on the growth of the cortex in thickness (Sugita, '17 a) shows all the localities measured in the cortex to undergo the same relative increase in thickness between birth and maturity, and always to stand in the same relation to one another, the doubts with regard to the general value of these particular results are largely removed.
9. Considered all together, the data on the development of the cerebral cortex indicate that it has been completely organized in the albino rat at the age of twenty days. The further development after this age represents a maturing of the elements. The completion of the cerebral organization corresponds to the
96 NAOKI SUGITA
weaning time of the rat.. If the cerebral organization of the rat brain at five days of age is similar to that of the man at birth, and the growth processes in the rat are thirty times as rapid as in man, then the completion of the cortex which occurs in the rat brain at twenty days should occur in the human brain at about fifteenth month of age.
PART II
ON THE AREA OF THE, CORTEX AND ON THE NUMBER OF CELLS IN A UNIT VOLUME, MEASURED ON THE FRONTAL AND SAGITTAL SECTIONS OF THE BRAIN OF THE NORWAY RAT (mUS NORVEGICUS), AND COMPARED WITH THE CORRESPONDING DATA FOR THE ALBINO RAT
VI. INTRODUCTION
In the Part I of this paper, I have presented the data on the area of the cerebral cortex measured on the sagittal and the frontal sections of the Albino rat brain and on the number of nerve cells in a unit volume of the cerebral cortex, and, by calculations based on these data, I have come to the conclusion that the entire volume of the cerebral cortex is increasing most rapidly during the first ten days after birth, while from twenty days onwards it increases at a lower rate than the entire cerebral volume. Further, the computed number of nerve cells in the entire cerebral cortex also increases very rapidly during the first ten days after birth and attains nearly its complete number at the age of twenty days.
I now wish to compare these relations in the Albino with those in the Norway rat, in the same manner as I have already done in the matter of the growth of the brain in size (Sugita, '18) and of the thickness of the cortex (Sugita, '18 a).
Employing for the Norway brains the sections on which the cortical thickness was measured earlier and for which the individual body measurements have been already given in table 1 in mj^ fourth paper (Sugita, '18 a), I have measured the area
GROWTH OF THE CEREBRAL CORTEX 97
of the cortex in the sagittal and the frontal section, following methods of measurement just described (part I) in the case of the Albino rat. Correction of the observed values to the values in the fresh condition of the material was also made by the use of the correction-coefficients obtained in the same way as those used for the Albino.
This study was made between March and May, 1917, at the Wistar Institute of Anatomy and Biology.
VII. MEASUREMENTS AND ENUMERATIONS
A'. Area of the cortex in the sagittal section {Nonvay rat)
Table 8 shows the observed and corrected areas of the cerebral cortex in the sagittal section of the Norway brain, also the data for the correction-coefficient for each individual, and the correction-coefficient for each brain weight group. The method of measurement and the positions of the borderlines of the measured area have been already described in part I of this paper, so that the explanations need not be repeated here (fig. 1). Chart 3 (graph s) has been plotted on the basis of table 8.
L. Area of the cortex in the frontal section {Nonvay rat)
Table 9 gives the observed and corrected areas of the cortex and the total area of the frontal section (one hemicerebrum) of the Norway brain with the data for the correction-coefficient for each individual and the correction-coefficient for each brain weight group. It gives also the percentage of the cortical area to the total area of the section. Chart 3 shows also in graphs (graphs F and f) the corrected data given in table 9.
M. Number of nerve cells (Norway rat)
Table 10 gives the observed and corrected number of nerve cells in a unit volume of 0.001 mm.-^ (0.1 mm.- in area and 0.01 mm. in thickness) at a fixed locality (locality VII) of the cortex in the frontal section, for each individual and for each brain weight group. The locality was chosen at a middle part of the cortical band in the frontal section as shown in figure 2, VII,
9.8
NAOKI SUGITA
for the Albino rat. The numbers of cells in the lamina pyramidalis and in the lamina ganglionaris respectively and the number of ganglion cells only in the lamina ganglionaris in five adjoining squares, each 100 micra on each side, were counted and the numbers in the unit volume of 0.001 mm. computed (see part I) and recorded in table 10. The relative cell density
^
F
^
.^
^y
/
■
«
1
1 1
10 11 1.2 13 14- 15 16 IT 1& 1.9 2.0 2.1 22 23 jws.
Chart 3 Showing the areas of the cerebral cortex in the sagittal and the frontal sections and the areas of the whole frontal section according to the brain weight. Norway rat. This chart is comparable with chart 1, which gives the corresponding graphs for the albino rat. X — . — . — Xs Cortical area in the
sagittal section. • 'f, Cortical area in the frontal section. •——•F, Area of
the whole frontal section. All graphs were based on the data in tables 8 and 9.
represented by the sum of the numbers of nerve cells in the lamina pyramidalis and the lamina ganglionaris is tabulated in table 16, column D, and plotted in chart 4 as graph N' .
VIII. DISCUSSION AND COMPARISON
The foregoing data, treated in a manner similar to that adopted in the case of the Albino (part I), may now be used for discussion and comparison.
TABLE 8
Showing the observed and corrected values of the area of the cerebral cortex in the sagittal section of the Norway rat brain, accompanied by the data for the correction-coefficient in the individual cases and the correction-coefficient for each brain weight group. L. F is the longitudinal diameter of the cerebrum
CORRECTION-COEFFICIENT
BR.\IN WEIGHT
OBSERVED
.\RE.\^ OF CORTEX
CORRECTED
GROUP
L.F
on fresh brain
The same
on slide
.\RE.4.
OP CORTEX
aravix
mm.'
m m .
m m .
Hi m .2
N XI b
1.155
18.4
11.75
10.40
23.5
a
1.160
17.0
12.10
10.15
24.2
i
1.175
14.2
12.55
9.60
24.3
1.163
16.5
l.'A
?P
24.0
NXII
N XIII a
1.369
16.7
12.95
10.10
27.5
1.369
16.7
l.i
W
27.5
NXIVb
1.407
18.2
13.45
10.50
29.8
g
1.429
16.3
13.05
10.10
27.2
a
1.431
19.1
13.15
10.40
30.6
i
1.431
18.1
13.05
10.25
29.4
e
1.437
15.8
12.80
10.05
25.7
k
1.445
19.2
13.35
10.30
32.3
1.430
17.8
l.i
W
29.2
N XV c
1.517
16.4
12.70
10.10
26.0
e
1.557
17. 3
13.75
10.30
30.8
1.537
16.9
l.t
w
28.4
N XVI a
1.619
17.2
13.50
10.20
30.2
g
1.632
16.8
13.45
9.75
32.0
e
1.636
15.9
13.55
10.00
29.2
1.629
16.6
l.t
w
30.5
N XVII e
1.710
18.8
13.70
10.40
32.6
g
1.721
18.7
13.40
10.20
32.3
a
1.738
16.8
13.60
10.40
28.8
c
1.788
20.1
14.20
11.00
33.5
1.739
18.6
l.i
w
31.8
N XVIII c
1.825
18.1
14.30
10.70
32.4
a
1.833
22.0
14.20
11.50
33.5
1.829
20.1
1.28'
33.0
100
NAOKl SUGITA
TABLE S— Continued
BRAIN- WEIGHT
OBSERVED
AHE.\ OF CORTEX
C ORRECTION-COEFFICIEXT
CORRECTED
GROUP
L.F
on fresh brain
The same
on slide
ARE.\
OF CORTEX
grains
mm.
mm.
mm.
m m .
N XIX b
1.962
19.9
14.70
11.25
34.1
a
1.981
19.5
14.40
11.00
33.5
1.972
19.7
1.31-'
33.8
NXXc
2.015
20.6
14.55
11.30
34.2
a
2.089
20.7
14.95
11.80
33.3
2.052
20.7
1.28'
33.8
NXXIg
2.156
21.1
15.15
11.90
34.2
d
2.187
20.2
15.30
11.50
35.7
2.172
20.7
l.t
w
35.0
NXXII
N XXIII a
2.345
22.4
14.50
11.50
35.7
2.345
22.4
1.26'
35.7
N. The area of the cortex in the sagittal section. Norway rat compared with the Albino
Table 11 shows the relations between the cortical area in the sagittal section and the longitudinal diameter of the cerebrum (L. F). Column B gives the average brain weight by groups, column C the average area of the cortex in the sagittal section, column D the average cortical thickness in the sagittal section {T ), column F the longitudinal diameter of the cerebrum (L. F), all of these being the corrected values. In column E the value C ; D or relative length of the long side, when the cortical area was reduced to a rectangle with the short side equal to the cortical thickness, appears. iVs shown in column G a.s E IF. these computed lengths show similar ratios when divided by the actual diameters L.F (column F), that is, 1.16 to 1.24 or on the average 1.20 for Groups N XI-N XXIII, but 1.19 for Groups N XIIIJN^ XX.- If necessary, therefore, the cortical area in the sagittal
GROWTH OF THE CEREBRAL CORTEX
101
TABLE 9
Showing the observed and corrected value's of the area of the cerebral cortex and of the total section in the frontal section and the -percentage of the cortical area in the total frontal section of the Norway rat brain, accompanied by the data for the correction-coefficient in the individual cases and the correction-coefficient for the group. W. D is the frontal diameter of the cerebrum,
OBSERVED
CORRECTIONCOEFFICIENT
CORRECTED
PERCENTAGE OP
BRAIN
WEIGHT
CORTICAL
GROUP
Area of
cortex
Area of
total
section
W.D
in fresh brain
The
same on
slide
Area of
cortex
Area of
total section
AREA
IN TOTAL
SECTION
gra ms
vim.
»jm.2
mm .
m m .
mm.
mm .2
per cent
NXIb
1.155
13.8
28.1
13.00
10,00
23.4
47.5
49
a
1.160
12.8
27.9
12.70
9.80
21.5
47.0
46
i
1.175
10.9
23.6
12.50
8.80
22.1
47.7
. 46
1.163
12.5
26.5
1..
u
22.3
47.4
47
NXII
N XIII a
1.369
13.7
27.9
13.00
9.80
24.2
49.2
49
1.369
13.7
27.9
l.i
?32
24.2
49.2
49
N XIV b
1.407
14.0
27.8
13.05
9.50
26.5
52.7
!o
g
1.429
14.0
28.5
13.20
9.50
27.1
55.0
49
a
1.431
14.6
30.4
12.85
10.20
23.2
48.4
48
i
1.431
14.9
29.6
13.40
10.30
25.3
50.2
50
e
1.437
12.6
28.7
13.25
9.60
24.1
54.1
44
k
1.445
13.2
28.4
13.30
9.50
26.0
55.8
47
1.430
13.9
28.9
1.35-^
25.4
52.7
48
NXVc
1.517
13.0
29.0
13.20
9.60
24.7
55.0
45
e
1.557
12.7
25.7
13.50
9,20
27.4
55.4
49
a
1.564
14.1
29.0
13.50
9.80
. 26.8
55.0
49
1.546
13.3
27.9
lA
.0=
26.3
55.1
48
N XVI a
1.619
14.7
31.3
13.80
10.50
25.4
54.2
47
g
1.632
13.8
27.6
13.70
9.50
28.8
57.6
50
e
1.636
13.2
28.2
13.80
9.60
27.3
58.2
47
1.629
13.9
29.0
1.^
.0'
27.2
56.7
48
N XVII e
1.710
13.4
29.5
13.80
9.70
27.2
59.8
.44
g
1.721
15.7
32.1
13.60
10.10
28.5
58.4
49
a
1.738
15.2
33.2
, 14.10
10.60
27.0
58.8
46
c
1.788
15.0
30.7
13.95
10.10
28.6
58.6
49
1.739
U.8
31.4
1.37-^
27.8
58.9
47
102
NAOKI SUGITA
TABLE 9— Continued
BRAIN WEIGHT
OBSERVED
CORRECTIONCOEFFICIENT
CORRECTED
PERCENTAGE OF
CORTICAL
Area of
cortex
Area of
total
section
W. D
in fresh brain
The
same on
slide
Area of
corte.x:
Area of
total
section
AREA
IN TOTAL
SECTION
grams
mm.
mm .
m m .
mm.
7)1 m.
mm.
per cent
N XVIII c
1.825
15.0
32.3
14.45
10.30
29.6
63.7
47
a
1.833
19.0
39.2
13.95
11.20
29.5
61.0
49
1.829
17.0
35.8
1.32
29.6
62.4
48
NXIXb
1.962
16.6
36.6
14.60
11.20
28.3
62.3
44
a
1.981
15.3
32.9
13.95
10.30
28.1
60.5
47
1.972
16.0
34.8
1.33'
28.2
61. 4
46
NXXc
2.015
14.6
33.1
14.30
10.20
28.7
65.2
44
a
2.089
15.7
35.5
14.50
10.95
27.6
62.3
44
2.052
15.2
3^.3
1.36^
28.2
63.8
u
N XXI g
2.156
15.1
35.1
14.75 10.70
28.7
67.0
43
d
■2.187
15.3
34.0
15.05 10.70
30.3
67.4
45
«
2.172
15.2
3J^.6
1.39-^
29.5
67.2
44
section may be calculated by the following formula, in which Ts denotes the average cortical thickness in the sagittal section.
L. F X T^X 1.20
(L. F and T^,, in millimeters)
The corresponding coefficient was found to be 1.22 in the Albino brains weighing more than 0.5 gram (table 4), but 1.20 for brains weighing more than 1.3 grams (Groups XIII-XX). The coefficients in the two forms may therefore be considered similar, that for the Albino being a trifle the larger.
If comparison is made between the absolute values of the cortical areas in the sagittal sections of the Norway and the Albino brains of like weight, no great difference appears (table 12). In the pair of Groups N XI and XI, the Norway is 10 per cent smaller in the area. This may be explained by the fact that the Norway brain weighing 1.16 grams is in a younger stage of cortical development, as compared with the Albino brain of like weight, the cortex of which is already provided with nearly all its nerve elements. But, in the pairs of Groups N XIII-XIII
GROWTH OF THE CEREBRAL CORTEX
103
TABLE 10 Giving for each individual and for each hrain weight group the number of nerve cells in 0.001 mm.^ of the cerebral cortex, in the lamina pyramidalis and in the lamina ganglionaris , and also the number of the ganglion cells only in the same volume of the lamina ganglionaris, counted at locality VII in the frontal section, as shown in fig. 2. Norway rat
BRAIN WEIGHT
CORRKCriOXCOEFFICIENT
XU.MBER OF CELLS IX .\ VOLU.MB
0.001 MM.-"
OF CORTEX,
GROUP
ir. D
in fresh brain
W.D
on slide
Lam. p.
•raniid.
Lam. ganglion.
Ganglion cells
in lam. gangl.
Observed
Corrected
Observed
Corrected
Observed
Corrected
grams
mm.
mm.
N XI b
1.155
13.00
10.00
253
115
170
78
44
20
a
1.160
12.70
9.80
242
111
164
76
41
19
i
1 . 175
12.50
8.80
271
95
199
69
48
17
1 . 163
(1/1
34)'
255
107
178
74
44
19
NXII
N XIII a
1.369
13.00
9.80
225
96
164
70
45
19
1.369
{1/1.33)^
225
96
164
70
45
19
N XIV b
1.407
13.05
9.50
243
94
174
67
46
18
g
1.429
13.20
9.50
227
85
176
65
48
18
a
1.431
12.85
10.20
200
100
142
71
40
20
i
1.431
13.40
10.30
222
101
175
79
47
21
e
1.437
13.25
9.60
225
86
165
63
49
19
k
1.445
13.30
9.50
230
84
178
65
51
19
1430
il/l
35)^
225
92
168
68
47
19
NXVc
1.517
13.20
9.60
235
90
169
65
52
20
e
1.557
13.50
9.20
250
79
176
56
58
IS
a
1.564
13.50
9.80
208
79
166
63
55
21
1.546
{l/l
40)'
231
83
170
61
55
20
NXVIa
1.619
13.80
10.50
203
90
143
63
50
22
g
1.632
13.70
9.50
235
78
159
56
60
20
e
1.636
13.80
9.60
214
72
164
55
57
19
1.629
{1/1
40)^
217
80
155
58
56
20
N XVII e
1.710
13.80
9.70
213
74
155
54
58
20
g
1.721
13.60
10.10
182
75
147
60
54
22
a
1.738
14.10
10.60
190
81
131
56
54
23
c
1.788
13.95
10.10
192
73
142
54
53
20
1.739
{1/1. 37Y
194
76
lU
56
55
21
104
NAOKI SUGITA
TABLE 10— Continued
'
BRAINWEIGHT
CORRECTIONCOEFFICIENT
NUMBER OF CELLS IN A VOLUME OF CORTEX,
0.001 MM. 3
■ GROUP
\V. D
in fresh brain
W.D
on slide
Lam. pyramid.
Lam. ganglion.
Ganglion cells
in lam. gangl.
Observed
Corrected
Observed
Corrected
Observed
Corrected
N XVIII c
a
NXIX b
a
NXXc
a
NXXIg
d
grams
1.825 1.833
1.829
1.962 1.981 1.972
2.015 2.089 2.052
2.156
2.187 2.172
mm.
14.45 13.95
(1/1
14.60 13.95
(1/1
14.30 14.50
(1/1
14.75 15.05
(.1/1
?nm.
10.30 11.20
32)^
11.20 10.30
33y
10.20 10.95
36y
10.70 10.70
39y
200
147
174
164 176
170 ■
189 170
180
180 186
183
• 73
76
75
74 71 73
69
74
72
69 67 68
146
114
130
120 134
127
140 116
128
118 120
119
53
59
56
54
54 54
51 50
51
45 43
u
55
42
49
45
48 47
49 44
47
45 46
46
20
22
21
20 19
20
18 19 19
17
17
17
to N XX-XX the Norway shows a sHght excess in the area ; on the average 2 per cent.
In spite of the fact that an adult Norway brain has a thicker cortex (by about 6.7 per cent in the sagittal section) than the Albino brain of the same weight, yet between the two a smaller difference in the area of the cortex in the sagittal section is found, because of the shorter longitudinal diameter of the cerebrum (L. F) in the Norway (Sugita, '18).
0. The area of the cortex in the frontal section, pared with ihe Albino
Norway rat com
bust as in the case of the sagittal section, table 13 shows relations between the cortical area in the frontal section and the
frontal diameter of the cerebrum iW. D). As a result, we see
that the relative value C/D or ^ ,.- i -, • , stands almost
' Cortical thickness
in a fixed ratio to the frontal diameter TF. D, that is, from 0.94
GROWTH OF THE CEREBRAL CORTEX
105
TABLE 11
Shotving relations between the cortical area in the sagittal section and the sagittal diameter of the cerebrum (L. F). Column E gives the relative lengths of the long side when the area is reduced to. a rectangle with the short side equal to the cortical thickness. These values have almost a fixed ratio to the sagittal diameter of the cerebrum (L. F) in each group, the average being 1.20. For the ex-planation see the text
A
B
C
D
E
P
G
' BRAIN WEIGHT
GROUP
BRAIN
WEIGHT
CORTICAL
AREA IN
S.^GITTAL SECTION
CORTICAL
THICKNESS
IN SAGITTAL
SECTION
c
D
L.F
E
F
grams
TO?«2
mm.
mm..
mm.
NXI
1.163
24.0
1.61
14.9
12.2
1.22
NXII
NXIII
1.369
27.5
1.73
15.9
13.1
1.21
NXIV
1.430
29.2
1.84
15.9
13.2
1.21
NXV
1.537
28.4
1.82
15.6
13.5
1.16
NXVI
1.629
30.5
1.88
16.2
13.6
1.19
NXVII
1.739
31.8
1.94
16.4
13.9
1.18
N XVIII
1.829
33.0
1.93
17.1
14.3
1.20
NXIX
1.972
33.8
1.97
17.2
14.6
1.18
NXX
2.052
33.8
1.92
17.6
14.7
1.17
NXXI
2.172
35.0
1.99
17.6
15.1
1.17
NXXII
N XXIII
2.345
35.7
1.86
19.2
15.5
1.24
Average (Groups N XI-N XXIII)
1.20
'
Average (Groun.s N XIIT-N XX^
1.19
to 1.00 or on the average 0.97 for Groups N XI-N XXI, so that the cortical area in the frontal section may be obtained by the following formula, in which T^ denotes the average cortical thickness in the frontal section:
W. D X T^ X 0.97 (W. D and T,-, in millimeters)
For Groups N XIII-N XX, the coefficient is 0.98 (table 13). The corresponding coefficient in the Albino, Groups XIII-XX, is about 0.93, as shown in table 5. Comparing the absolute values of the cortical area in the frontal sections in two forms of like brain weight group (Groups N XIII-N XX to Groups XIII-XX), we find that in the Norway it is on the average larger by about 10 per cent (table 12).
106
NAOKI SUGITA
TABLE 12
Com/parison of the Norway rat brain with the Albino rat brain of like weight in the areas of the cortex^ in the sagittal and the frontal sections and in the area of the total frontal section. The data were taken fram tables 1, 2, 8 and 9
BRAIN WEIGHT GROUP
BRAIX
WEIGHT
AREA OF
CORTEX INSAGITTAL
SECTIOX
AREA OF
CORTEX IN
FRONTAL
SECTION
AREA OF
TOTAL FRONTAL
SECTION
Albino
Norway
Albino
Norway
Albino
Norway
Albino
Norway
gram s
grams
mm.
TOm.2
7mn .2
mm.^
mm. 2
TO TO. 2
XI
1.171
1.163
26.6
24.0
21.7
22.3
45.7
47.4
XII
1.253
26.1
23.0
47.2
XIII
1.335
1.369
27.6
27.5
23.2
24.2
50.2
49.2
XIV
1.445
1.430
28.2
29.2
24.8
25.4
52.3
52.7
XV
1.554
1.542
28.7
28.4
24.3
26.3
54.0
55.1
XVI
1.656
1.629
29.2
30.5
24.3
27.2
54.9
56.7
XVII
1.726
1.739
31.1
31.8
24.6
27.8
56.4
58.9
XVIII
1.839
1.829
32.8
33.0
26.0
29.6
58.9
62.4
XIX
1.924
1.972
32.3
33.8
24.8
28.2
57.0
61. 4
XX
2.054
2.052
33.7
33.8
24.9
28.2
63.4
63.8
XXI
2.172
35.0
29.5
67.2
XXII
XXIII
2.345
35.7
Average for Groups XIII
XX
1.692
1.695
30.5
31.0
24.6
27.1
55.9
57.5
The total area of the frontal section is also slightly in favor of the Norway (table 12).
P. Percentage of the urea of the cortex to the lotal area of the frontal
section (one hemicerehrum) . Norway rat compared
with the Albino
As for the percentage of the cortical area to the total area of the section, a comparison between the two forms is interesting. In the Albino this percentage value increases from birth to a brain weighing 0.7 to 1.2 grams when it attains the value of about 48 per cent (table 2), but in the Norway the highest percentage is attained in brains weighing 1.1 to 1.8 grams. This indicates that the cortical organization is more retarded in the Norway, if the brain weight be taken as the basis of comparison. In a fully mature Norway brain (from Group N XX onwards,
GROWTH OF THE CEREBRAL CORTEX
107
TABLE 13 Showing relations between the cortical area in the frontal section and the frontal diameter of the cerebrum {W. D). Column E gives relative lengths of the long side ivhen the area is reduced to a rectangle toith the short side equal to the cortical thickness. These values have almost a fixed ratio to the frontal diameter of the cerebrum {W. D) in each group, the average being 0.97. For the detailed explanation see also the text. Norway rat
A
B
C
D
E
F
G
CORTICAL
CORTICAL
BRAIN WEIGHT
B BAIN
AREA IN
THICKNESS
C
ir D
E
GROUP
WEIGHT
FRONTAL
SECTION
IN FRONT.\^L
SECTION
D
F
grams
mm.
vim.
vim.
mm.
NXI
1.163
22.3
1.88
11.9
12.7
0.94
NXII
NXIII
1.369
24.2
1.96
12.3
13.0
0.95
NXIV
1.430
25.4
1.95
13.0
13.2
0.98
NXV
1.546
26.3
2.04
12.9
13.4
0.96
NXVI
1.629
27.2
2.08
13.1
13.7
0.96
N XVII
1.739
27.8
2.07
13.4
13.9
0.96
N XVIII
1.829
29.6
2.08
14.2
14.2
1.00
NXIX
1.972
28.2
2.00
14.1
14.3
0.99
NXX
2.052
28.2
1.96
14.4
14.4
1.00
NXXI
2.172
29.5
2.08
14.2
14.9
0.95
Average (Gro
ups N XI
N XXI) . . .
0.97
Average (Gro
ups N XIIT-N XX)
0.98
table 9) this percentage amounts to 44 per cent, which is equal to that seen in the mature Albino brain (Groups XVI to XIX, table 2), if we disregard one case of advanced age (Group XX).
Q. Number of cells in a unit volume of the cortex, compared with the Albino
Norway rat
Reviewing table 10 which gives separately the numbers of nerve cells in the unit volume of 0.001 mm.^ of the lamina pyramidalis and the lamina ganglionaris at a fixed locality m the frontal section of the cerebrum and counted by the same method used for the Albino rat and comparing these numbers with those in table 3 in part I, it is easily seen that, if the like brain weight groups of the two forms are paired, the number of cells in the unit volume of both layers is slightly lower in the Norway rat.
108
NAOKI SUGITA
These relations are shown in table 14. As for the number of the ganghon cells only in the lamina ganglionaris, it is always lower by 2 to 6 in the Norway and the highest figure (21) in the Norway is seen in Groups N XVII and N XVIII, while in the Albino the highest figure (25) is attained in Groups- XIII and XIV and again in Group XVII. In the Albino a temporary increase of cell number in the lamina ganglionaris was seen in Groups XIII and XIV, and in my Norway sections a similar phenomenon is indicated in Groups N XVII and N XVIII. Generally speaking, therefore, the cell densit}^ in the cerebral cortex, as far as represented by my observations, is slightly
600 ■i'in
X
•r^
.---'
--°
'•^
^o—
-o —
■^
.•
-~.y
350
300
^
^
-LV\
H'
200
_
rr
^:
^
100
"~"
—
—
—
— ~-r
M
50
1
do 11 12 1.3 14 d.5 1.6 L7
1.9 2.0 2.1 2.2 2.3 2.4
yns.
Chart 4 Showing the computed values for the cortical volume, the volume of the cerebrum, the cenn density in two unit volumes and the computed number of nerve cells in the entire cortex of the Norway rat, according to the brain weight. This chart is equivalent to, but not directly comparable with chart 2, which gives the similar data in the Al'bino in ratios of the values at birth. • •LWT', The computed volume of the cerebral cortex, based on table 15.
hWH' , The relative volume of the entire cerebrum, based on the data
presented in a former paper (Sugita, '18) and given also in table 15. X— — XN', The cell density in two unit volumes of the cortex. Graph based on the data
given as N in column D, table 16. -" — ^NLWT', The computed number of
nerve cells in the entire cortex, based on the figures given in column E, table 16. Mark X shows the phase in growth corresponding to that indicated by the same mark in chart 2, which shows the end of the second developmental phase in the Albino.
GROWTH OF THE CEREBRAL CORTEX
109
TABLE 14. Comparison of the Norway rat brain with the albino rat brain of lilie weight for the nuvibers of nerve cells in the lamina pijramidalis and in the lamina ganglionaris and the number of ganglion cells only in the lamina ganglionaris, in a unit volume of 0.001 mm.^, and also for N, which is the sum of the numbers in the lamina pyramidalis and in, the lamina ganglionaris. The data were taken from tables 3 and 10
NUMBER OF
CELL.S
IX .4 UNIT VOLUME
N,
OF
ORTEX
0.001
MM. 3
THE SUM OF
DRAIN
WEIGHT
NUMBERS
DRAIN WEIGHT GROUP
Lam.
pyrani .
Lam .
gangl.
Ganglion
cells in lam.
gangl.
OF CELLS IN
L.iM. PYR.
AND IN
LAM. GANG.
Al
Nor
Al
Nor
Al
Nor
Al
Nor
Al
Nor
bino
way
bino
way
bino
way
bino
way
bino
way
grams
grams
XI
1.171
1.163
113
107
73
74
23
19
186
181
XII
1.253
103
68
23
171
XIII
1.335
1.369
99
96
77
70
25
19
176
166
XIV
1.445
1.430
94
92
71
68
25
19
165
160
XV
1.554
1.546
87
83
62
61
23
20
149
144
XVI
1.65G
1.629
84
80
60
58
24
20
144
138
XVII
1.726
1.739
83
76
63
56
25
21
146
132
XVIII
1.839
1.829
79
75
59
56
23
21
138
131
XIX
1.924
1.972
81
73
51
54
24
20
132
127
XX
2.054
2.052
80
72
51
51
20
19
131
123
XXI
2.172
68
44
17
112
Average for Groups
XIII-XX
1.Q92 1. 695
86
81
62
60
24
20
148
140
lower in the Norway rat, if the brain weight be selected as a standard of comparison.
/?. The computed volume of the entire cerebral cortex, compared with the Albino
Norumij rat
The computed volume of the cerebral cortex for the Norway may also be obtained and expressed in values comparable among themselves, by the use of the formula: L. F X W. D X T (where T denotes the mean thickness of the cortices in the sagittal and the frontal sections), as already explained in detail in part I (see p. 82). But for a comparison between the cortical volumes of the Norway and of the Albino brains, the direct comparison
THE JOURNAL OP COMPARATIVE NEUROLOGY, VOL. 29, NO. 2
110 NAOKI SUGITA
of the values obtained by the above fonnuhxs is not allowable, since, comparing the areas in the Albino among themselves, the fixed coefficients"' 1.21 and 0.93 were ehminated from the formula, as already stated, and similarly in the Norway the corresponding coefficients'^ 1.19 and 0.98 were also eliminated from the formula. In order to compare the areas in these two forms, the coefficients must be taken into consideration. As the product 1.19 X 0.98 is higher by 3.6 per cent than theproduct 1.21 X 0.93, the value of L. F X W.D X T for the Norway should be raised by 3.(3 per cent to be directly comparable with the \'alue of L. F X
1 1 Q V 98 IF. D X T for the Albino. The ratio =,','! r^L (= 1-03(3)
1.21 X 0.93 ^
being represented by C, the comparable value of the cortical
volume for the Norway may be obtained by the corrected formula
as follows:
L. F X W. D X T XC (C ^ 1.036)
Table 15 gives the computed cortical volume of the Norway brain, obtained according to the above corrected formula, and this is shown graphically in chart 4 (graph LWT').
As the available data in the Norway do not extend to the earlier ages, I could not determine the early increase in the cortical volume of the Norway, but our data show that the cortical volume is increasing somewhat more rapidly during the period when the brain weight is increasing from 1.16 to 1.54 grams and after that it increases more slowly but steadily as the entire cerebral volume increases, as shown in table 15 and in chart 4 (graph LWH'). In the Albino, as has been shown, the cortical volume increases relatively rapidly until the brain attains 1.17 grams in weight, a phase which probably corresponds to the phase in the Norway of 1.43 grams in brain weight.
To compare the cortical volume in the Norway rat with that of the Albino, I have paired, in table 15, the Norway data {L. F XW. D X T X C] directly with the corresponding Albino
- For a proper (;onii)arisoii, the eoeflficieuts here used are those for the same
brain weight groups compared in both forms, l)eing respectively the averages for Groups XIII to XX and for Groups N XIII to N XX, taken from tables 4, 5, 11 and 13.
GROWTH OF THE CEREBRAL CORTEX
111
TABLE 15
Showing the computed volume for the entire cerebral cortex of the N'orway rat hraiii, calculated by the formula: L.F X W. D X T X C for each brain iveight group, C being a fixed coefficient used to convert the computed volume of the Norway cortex so as to make it comparable with that of the Albino {C = 1.036). The computed volume of the cerebrum is quoted from my previous presentation (Sugita, '18). These values are paired ivith the corresponding values for the cortical volume of the Albino and the ratios between them, calculated
NORWAY RATS
ALBINO RATS
A
B
C
D
E
F
G
H
I
Brain weight
group
Brain
wciglit
Computed
volume
of
cerelirum
L.G X W.DXHt.
L.F
in fre.sli
brain
\V. D
in fresh
brain
average
cortical
thickness
L.FX
W. D XT
XC
Computed
volume
of corte\
Corresponding
computed
volume
of the
Albino
cortex, of
the same
group
number
Ratio
of cortical
volume
of the
Norwav
to that of
the
Albino
grams
)H tn .3
mm .
)// m .
m m .
mm .^
7)1 m.^
NXI
1.163
156
12.2
12.7
1.75
281.00
288.93
0.973
NXII
304.51
NXIII
1.369
182
13.1
13.0
1.85
326.51
314.03
1.040
NXIV
1.430
185
13.2
13.2
1.90
343.09
329.71
1.040
NXV
1.537
194
13.5
13.4
1.93
361.83
345.86
1.046
NXVI
1.629
203
13.6
13.7
1.98
382.32
359.30
1.064
NXVII
1.739
218
13.9
13.9
2.01
402.47
365.08
1.102
N XVIII
1.829
226
14.3
14.2
2.01
423.00
397.96
1.063
NXIX
1.972
241
14.6
14.3
1.99
430.57
390.39
1.103
NXX
2.052
249
14.7
14.4
1.94
425.59
393.15
1.0S3
NXXI
2.172
264
15.1
14.9
2.04
475.66
Average
(Groups
N XIII
N XX) .
386.92
361.94
1.069
1 T, here entered, is the mean value of T, and Tp, previously given in tables 11 and 13 and is not the general average thickness of the corte.x of the sagittal, frontal and horizontal sections formerly presented in my fourth paper in this series (Sugita, '18 a).
data (L. F X W. D X T) according to the brain weight groups, quoted from part I. In table 15 the ratios show the volume of the cortex in the Norway to be greater (1.040 to 1.103) in all the comparisons for brain weights above Groups XIII (brain weight 1.87 grams). The average value is about 1.07. In Group XI (brain weight 1.17 grams), the ratio for the Norway is less than 1. At this weight the Norway brain is regarded as less mature than
112 NAOKI SUGITA
the corresponding Albino brain. The ratio tends to increase as the brain weight increases, showing roughly the relative growth in the Norway cortex.
Since, as has been shown (Sugita, '18 a), the cortex in the mature Norw^ay is about 8 per cent thicker (average of the sagittal and frontal sections) than in the Albino, and since this value enters as T into the formula under discussion, this would tend to give a greater \'olume of the cortex in the Norway than in the Albino. The mean value found for the ratio of the cortical volume — 1.07 — is about that to be expected, in view of the relatively smaller value of L. F in the Norway.
>S. Computed number of nerve cells in the entire cortex. Norway rat compared with the Albino
As described in part I, the computed number of nerve cells in the entire cerebral cortex may be obtained by the following formula :^
NXL.FX W. D X T XC (L.F, ]V. D and T, in miUimeters) where L. F X W. D X T X C is the computed volume of the Norway cortex made comparable directly with the corresponding volume for the Albino, as explained in the foregoing chapter, and A^ is the cell density, represented by the sum of the numbers of cells in a unit volume in the lamina pjTamidalis and in a unit volume in the lamina ganglionaris (two unit volumes altogether), given separately in table 10 and combined in table 16.
Table 16 gives the computed value of the cell number in the entire cerebral cortex for each brain weight group of the Norway rats (column E), calculated by the use of the above formula, and also in the corresponding case of the Albino (column G).
On examining table 16, column E, w^e find the computed number of nerve cells in the cortex to be nearly completed in a brain weighing 1.37 grams (Group N XIII), while in the Albino this condition was reached in a brain weighing 1.17 grams (Group XI). The value of the completed cell number is indicated in
The formula for the total number of nerve cells in the Norway cortex is like that for the Albino cortex with the addition of the factor C (footnote 4) .
GROWTH OP THE CEREBRAL CORTEX
113
TABLE 16
Giving the computed number of nerve cells in the entire cerebral cortex of the Norivay rat brain, obtained on the basis of the m.easurements given in this series of studies. These values are made to be comparable ivith the corresponding values of the computed number of nerve cells in the cortex of the albino rat brains of like brain weight groups
NORW.W R.\TS
ALBINO RATS
A
B
C
D
E
F
G
Brain weight
group
Brain weight
Computed
volume of
cortex
L.FX n'. D
XT XC
Sum of
numbers of
cells in lam. pyr.
and lam. gang, in two
unit volumes, N
Computed
number of cells
in entire
cortex,!
X XL.F
X It'. DXT
x^'x'iTo
Ratio of
number of
cells in the Norway
to that in the Albino
Corresponding
computed number of cells
in the
Albino, of the
same group
number
NXI
NXII
NXIII
NXIV
NXV
NXVI
N XVII
N XVIII
NXIX
NXX
NXXI
grams
1.163
1.369 1.430 1.537 1.629 1.739 1.829 1.972 2.052 2.172
m m .3
281.00
326.51 343.09 361.83 382.32 402.47 423.00 430.57 425.59 475.66
181
166 160 144 138 132 131 127 123 112
508.6
542.0 548.9 521.0 527.6 531.3 554.1 546.8 523.5 532.7
0.946
0.981 1.009 1.011 1.020 0.997 1.009 1.061 1.016
537.4
520.7
552.7
544.0
515.3
517.4
533.0
549.2
515.3
515.0
Average (Groups N XIII-N XX)
536.9
1.013
530.2
1 As remarked in a note to table 7, the number given in this column corresponds to 1/100 of N X L. F X W. D X T,or 1/50,000 of the actual number of cells contained in the computed volume of the cortex.
the Norway by about 537 (the average of Groups N XIIIN XX) or about 1 per cent more than that of the Albino, which has been indicated by about 530 (the average of Groups XIIIXX, see table 7), so that the number of nerve cells in the entire cortex of the mature Norway and of the Albino rats may be regarded as practically the same, as suggested by Donaldson (Donaldson and Hatai, '11).
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IX. CONCLUSIONS
Putting together the foregoing observations, we come to the conclusion that in the case of the Norway rat brain the entire volume of the cerebral cortex is actively increasing up to a brain weight of something more than 1.43 grams (Group N XIV) and that the number of nerve cells in the cortex is completed in a brain weighing something less than 1.43 grams (Group N XIV) (chart 4). After this, the increase in cortical volume keeps pace with the enlargement of the entire cerebrum, showing that the cortical mass and the remainder of the cerebrum are growing at the same rate. So, the end of the short period during which the brain has attained 1.37 to 1.54 grams in weight (Groups N XIII to N XV) marks an epoch in the development of the cerebral cortex of the Norway rat, at which the structural completion of the cortex has been acquired and the full preparation for the functional education has been established. This period corresponds approximately to the age of twenty days.
In the Albino, the same degree of development is reached when the brain attains a weight of 1.17 grams or is twenty days old. As I suggested in an earlier paper (Sugita, '18 a), a Norway brain corresponds in the development of the cortex to an Albino brain weighing about 18 per cent less. This assumption has held true in the present examinations of the cortical volume and cell number, because an Albino brain weighing 1.17 grams just corresponds to a Norway brain weighing 1.43 grams.
The number of cells in the Norway cortex has been shown to be but slightly (1 per cent) different from that in the Albino rat cortex and may be regarded as the same in both forms. This fact justifies at the same time a conclusion reached by Donaldson in his former comparison of the Norway with the Albino rats, that the greater weight of the brain in the Norway rat, compared with the Albino of the same body weight or of the same age, is probably due to an enlargement of the constituent neurons rather than to an increase in their number (Donaldson and Hatai, '11). The results of my study regarding the cell size in the cortex in these two forms will be discussed in a forthcoming paper and will support the statement just made.
GROWTH OF THE CEREBRAL CORTEX 115
X. SUMMARY
1. On the sagittal and the frontal sections from 28 Norway rats, whose brain weights fall between 1.1 and 2.4 grams and which were formerly used for the investigation on the cortical thickness (Sugita, '18 a), the area of the cortex was measured and the number of nerve cells, in a unit volume of 0.001 mm.^ at a fixed locality of the cortex, was counted. These values were all later corrected to the corresponding values in the fresh condition of the material, using the correction- coefficients devised for this purpose. These results have been grouped and averaged according to the brain weight and then compared with the corresponding data in the Albino, which were presented in part I of this paper.
2. The actual area of the cortex in the sagittal section may be obtained by the formula: L. F X T^X 1.20 (L. F and T^, in millimeters), where L. F is the longitudinal diameter of the cerebrum, T^ is the thickness of the cortex in the sagittal section and 1.20 is a constant coefficient which was empirically determined (table 11, column G).
3. The actual area of the cortex in the frontal section may be obtained, though less precisely, by the formula: W. D xT^ X 0.97 {W. D and T^ in millimeters), where W. D is the frontal diameter of the cerebrum, T^ is the thickness of the cortex in the frontal section and 0.97 is a constant coefficient which was determined empirically (table 12, column G).
4. The percentage of the cortical area to the area of the whole frontal section is highest (48 per cent) in brains weighing 1.1 to 1.8 grams. In a fully mature brain it has fallen to 44 per cent.
5. The computed value for the volume of the entire cortex, indicated by the formula: L. F X W. D X T X C (L. F, W. D and T, in millimeters), where L. F is the longitudinal diameter, W. D is the frontal diameter of the cerebrum, T is the average thickness of the cortex in the two sections and C a theoretically determined coefficient necessary to make the values directly comparable with the corresponding values for the albino rat, shows that the cortex is increasing relatively rapidly in the
116 NAOKI SUGITA
Norway brains weighing less than 1.43 grams. After that stage its increase nearly keeps pace with the increase in the volume of the entire cerebrum.
6. In Norway brains weighing from 1.1 to 2.2 grams, the cell density or the number of nerve cells in a unit volume of the lamina pyramidalis and the lamina ganglionaris, in a fixed locality of the cortex, decreases slowly but steadily as the brain weight advances. It has proved sHghtly less than that in the Albino (compare table 16, column D, with table 7, column C). In the lamina ganglionaris the number of ganglion cells onl}^ in a unit volume is at its highest in the brains weighing 1.7-1.8 grams (table 14).
7. The value for the computed number of nerve cells in the entire Norway cortex, indicated by the formula: A*^ X L. F X Wl D XT XC (L. F, W. D and T, in millimeters), where A^ is the number of cells in two unit volumes and L.F x W. D X T X C is the computed volume of the cortex, shows that it is almost completed in a brain weighing something more than .37 grams.
8. Comparisons in respect of the above characters between the Norway and the Albino brains of the like weight show that, in the cortical areas in the sagittal and the frontal sections and in the volume of the entire cortex, the Norway rat surpasses the albino rat, but the number of cells as computed for the entire cortex may be regarded as the same in both forms. We conclude therefore that the difference in absolute brain weight between the two forms is not correlated with a difference in the number of nerve cells in the cerebral cortex. In a Norway brain weighing 1.4 to 1.5 grams, which corresponds to an Albino brain weighing 1.17 grams and is about twenty days in age, the elemental organization of the cerebral cortex in the Norway rat is considered to be almost completed.
GROWTH OF THE CEREBRAL CORTEX 117
LITERATURE CITED
Allen, Ezra 1912 The cessation of mitosis in the central nervous system of the albino rat. Jour. Comp. Neur., vol. 22, no. 6.
Donaldson, H. H. 19 8 A comparison of the albino rat with man in respect to the growth of the brain and of the spinal cord. Jour. Comp. Neur. and Psychol., vol. 18, pp. 345-392.
1915 The Rat. Memoirs of The Wistar Institute of Anatomy and Biology, no. 6.
Donaldson, H. H. and Hatai, S. 1911 A comparison of the Norway rat with the albino rat in respect to body length, brain weight, spinal cord weight and the percentage of water in both the brain and the spinal cord. Jour. Comp. Neur., vol. 21, pp. 417-458.
Stjgita, Naoki 1917 Comparative studies on the growth of the cerebral cortex. I. On the changes in the size and shape of the cerebrum during the postnatal growth of the brain. Albino rat. Jour. Comp. Neur., vol. 28, no. 3.
1917 a Comparative studies on the growth of the cerebral cortex. II. On the increase in the thickness of the cerebral cortex during the postnatal growth of the brain. Albino rat. Jour. Comp. Neur., vol. 28, no. 3.
1918 Comparative studies on the growth of the cerebral cortex. III. On the size and shape of the cerebrum in the Norway rat (Mus norvegicus) and a comparison of these with the corresponding characters in the Albino rat. Jour. Comp. Neur., vol. 29, no. 1.
1918 a Comparative studies on the growth of the cerebral cortex. IV. On the thickness of the cerebral cortex of the Norway rat (Mus norvegicus) and a comparison of the same with the cortical thickness in the Albino. Jour. Comp. Neur., vol. 29, no. 1.
