Paper - Comparative studies on the growth of the cerebral cortex 1 (1917)
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Sugita N. 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. (1917) J Comp. Neurol. 28: 495-.
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Sugita N. Comparative studies on the growth of the cerebral cortex. II. On the increases in the thickness of the cerebral cortex during the postnatal growth of the brain. Albino rat. (1917) J Comp. Neurol. 28: 511-. Sugita N. 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. (1918) J Comp. Neurol. 29: 1-. Sugita N. 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 rat. (1918) J Comp. Neurol. 29: 11-. Sugita N. Comparative studies on the growth of the cerebral cortex. 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 c responding data for the albino rat. (1918) J Comp. Neurol. 29: 61-117. Sugita N. Comparative studies on the growth of the cerebral cortex. VI. Part I. On the increase in size and on the developmental changes of some nerve cells in the cerebral cortex of the albino rat during the growth of the brain. VI. Part II. On the increase in size of some nerve cells in the cerebral cortex of the Norway rat (Mus norvegicus), compared with the corresponding changes in the albino rat. (1918) J Comp. Neurol. 29: 119-. Sugita N. Comparative studies on the growth of the cerebral cortex. VII. On the influence of starvation at an early age upon the development of the cerebral cortex. Albino rat. (1918) J Comp. Neurol. 29: 177-. Sugita N. Comparative studies on the growth of the cerebral cortex. VIII. General review of data for the thickness of the cerebral cortex and the size of the cortical cells in several mammals, together with some postnatal growth changes in these structures. (1918) J Comp. Neurol. 29: 241-.
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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
From The Wistar Institute of Anatomy and Biology
Two Figures And Two Charts
I. Introduction
The present study is preliminary to an investigation on the postnatal growth of the cerebral cortex in thickness, in the case of the albino rat. For this purpose it was necessary to learn the changes in shape and size of brain — represented by the cerebrum — which occur during postnatal growth and to record these changes in terms of linear measurements.
The growth of the brain, as represented by increase in weight, is tabulated in "The Rat" (Donaldson, '15). As yet however we have no records concerning the shape and dimensions of the brain — or cerebrum — in relation to increasing weight or age. Hatai ('07) has given detailed measurements on the skull of mature albino rats, from which we can infer approximately the shape and size of the adult albino rat brain, but measurements for the younger stages were not included.
As a first step in this study, I had to ascertain the relation existing between the weight of the entire brain and of the cerebrum during growth. For the purpose of a more detailed study, Donaldson has divided the entire brain into four parts, i.e., the cerebrum, the stem, the cerebellum and the olfactory bulbs, and investigated the increase in weight of each of these parts and the changes in the weight relations among them, during postnatal growth (unpublished observations, partly presented in a Harvey Lecture, December, 1916) . From a like investigation on my part, on a small number of cases, the following may be reported. In table 1 are given for ten ages the total brain weights and their ratios, the weights of the parts and the ratios of the weights of parts to their respective initial weights at birth. It is seen from these data that throughout the early period of life (first 150 days), the cerebellum develops most rapidly, the olfactory bulbs show the next highest rate, while the stem develops rather steadily during that period. The cerebrum, however, develops in a ratio equal to that of the entire brain, from which fact we may conclude that the developmental stage of the cerebrum is fairly represented by that of the entire brain.
TABLE 1
Giving for ten ages the total brain weights and their ratios, the weights of the parts and the ratios of the weights of parts to their respective initial weights at birth, albino rat brain
NUMBER OF
.\GE
IN DATS
TOTAL BRAIN WEIGHT
CEREBRUM
CEREBELLUM
STEM
OLFACTORY BULBS
CASES
Observed
Ratio
Observed
Ratio
Observed
Ratio
Observed
Ratio
Observed
Ratio
4 4 3 2
4 3 2 5 4
B
4
5
20
35
50
60
70
90
150
grams
0.236 0.482 0.503 1.153 1.355 1.469 1.531 1.612 1.779 1.933
1.0 2.0 2.1 4.9 5.7 6.2 6.5 6.8 7.5 8.2
gram.s
0.150 0.338 0.349 0.817 0.870 0.974 0.959 1.033 1.121 1.191
1.0 2.3 2.3 5.4 5.8 6.5 6.4 6.9 7.5 8.0
grams
0.008 0.023 0.026 0.126 0.197 0.197 0.226 0.215 0.244 0.275
1.0 2.9 3.3 15.8 23.4 23.4 28.3 26.9 30.5 34.4
grams
0.073 0.105 0.113 0.171 0.248 0.258 0.278 0.331 0.337 0.373
1.0 1.4
1.5 2.3 3.4 3.5 3.8 4.5 4.6 5.1
grams
0.005 0.016 0.015 0.039 0.040 0.040 0.068 0.033 0.077 0.094
1.0 3.2 2
7.8
8.0
8.0
13.6
6.61
15.4
18.8
1 The olfactory bulbs are very variable in weight. Undeveloped bulbs like the above sometimes occur.
This preliminary examination was made to ascertain whether or not the developmental weight phases of the cerebrum are represented by those of the total brain weight. It appears that they are thus represented, so that total brain weights may be used when cerebrum weights are not available.
To study the developmental changes in the shape and size of the cerebrum, I selected five diameters of the entire cerebrum.
from the measurements of which its general shape and size can be closely determined.
The materials used in this study were all employed for the further investigation on the cortical development, including a study on the thickness of the cerebral cortex. The present research was begun in October, 1915, and concluded in June, 1916, at The Wistar Institute of Anatomy and Biology.
In connection with this study, which is the first of a series made during my stay in Philadelphia, I desire to express my sincere thanks to Dr. M. J. Greenman, Director of The Wistar Institute, for extending to me the privileges of the Institute and putting its facilities at my disposal — and also to acknowledge my obligations to Prof. Henry H. Donaldson under whose direction these researches have been made.
II. Material and Technique
The material, consisting of 141 albino rats (106 males, 32 females and 3, sex undetermined) — representing every phase of postnatal growth and having approximately standard body measurements — were all from the rat colony at The Wistar Institute. After dissection the entire brain was severed from the spinal cord by a transverse section at the level of the calamus scriptorius and weighed to a milligram in a weighing bottle. The brain was next put on a glass plate, base down, without any lateral support. Five diameters of the hemispheres were then measured with a sliding calipers to a twentieth of millimeter, according to the method to be later described.
These measured values are, of course, slightly different from the values of the same diameters taken on the hemispheres in situ within the skull, because normally the basal surface of the skull does not lie in a plane, but is slightly arched, and the sides are supported by the temporal walls of the skull. Thus, as measured, the height of the fresh brain is somewhat reduced and the width increased. To measure the brain in situ was however not satisfactory and I thought it better to bring the brain to a position convenient for measurement, in order to get more exact values. As I measured all the material in the same manner, the data thus obtained are comparable among themselves.
I have arranged the individuals in twenty groups, numbered according to the number of decigrams in the brain weight of each, for example, brains weighing 0.300-0.399 grams form Group III and brains weighing 1.500 to 1.599 grams Group XV, etc. In each group, the individual was designated as a, or b, or c, etc. in the order of the date of the dissection. Each individual carries the same designation when the record for it appears in the other studies in this series. Measurements of the body and brain weights, body and tail lengths, were made by the usual methods employed at The Wistar Institute (see The Rat," Donaldson, '15).
As the individual records will, for the most part, be given in a study, which follows, on the growth of the cortex, and as all of the records are on file at The Wistar Institute, it has not been thought necessary to print them here. In table 2, the mean values for each brain weight group are entered with a statement of the number of individuals on which the average has been based.
In table 2 are given for comparison the standard body weight and body and tail lengths and the age, corresponding to the observed brain weights, and obtained by the use of formulas devised by Hatai (see "The Rat," Donaldson, '15). Some discrepancies seen in the case of Groups XVI-XX between the observed and calculated values are due to the fact that in grown-up rats the brain weight increases very slowly, while the body measurements are open to wide variations.
III. Positions of Diameters
The positions of the five diameters, by measurement of which the §hape and size of an albino rat cerebrum are to be determined, are as follows (figs. 1 and 2).
1. Width AB (abbreviation W. B), the greatest width along the frontal plane (fig. 1).
2. Width CD (abbreviation W. D), passing through the middle point O of the fissura sagittalis and parallel to AB (fig. 1).
TABLE 2
The body measurements as observed are here compared with the standard values for the body measurements based on the observed brain weights and computed by the formulas devised by Hatai ("The Rat," Donaldson, '15)
BRAIN
NUMBER OF CASES
OBSERVED
ST.VNDARD
GROUP
Again days
Body weight
Body length
Tail length
Brain weight
Tail length
Body length
Body weight
Age in days
grams
mm.
mm.
grams
mm,.
mm.
grams
I
3
.1
3.0
38
14
0.161
II
10
B.
5.2
48
18
0.254
19
51
5.2
1
III
11
3
6.2
52
20
0.341
24
56
6.0
2+
IV
10
4+
7.7
56
23
0.424
27
58
6.7
4
V
19
6
9.6
61
27
0.544
31
61
8.0
6
VI
4
7
9.6
63
28
0.622
34
64
9.0
7
VII
7
8+
9.6
64
32
0.769
40
69
11.1
8+
VIII
10
9+
12.4
68
33
0.845
42
71
11.9
9+
IX
5
11 +
13.9
74
38
0.954
46
75
13.6
11
X
6
IS
15.5
76
46
1.047
51
80
15.8
15
XI
6
IS
16.1
78
50
1.156
59
87
19.7
20+
XII
6
(27)
25.8
92
69
1.253
68
96
24.9
26
XIII
7
28.1
99
73
1.334
77
105
31.1
32
XIV
5
55.8
125
102
1.449
93
121
44.4
41
XV
7
(50)
74.1
141
129
1.558
111
139
64.1
54
XVI
9
156.8
177
158
1.662
130
158
92.3
65
XVII
7
(100)
157.8
180
157
1.737
144
174
122.0
76
XVIII
5
184.3
188
160
1.832
164
194
175.0
107
XIX
1
2 years
300.2
225
195
1.924
183
215
250.5
205
XX
3
2 years
289.2
—
199
2.037
207
241
388.0
—
Prematurely born.
^ Rigor mortis.
Fig. 1 Dorsal view of the albino rat brain weighing 1.5 grams. Enlarged 1.8 diameters. To show the positions at which the two measurements for the width and the two measurements for the length were taken. AB = Width W .B, CD = Width W.D, EF = Length L.F and EG = Length L.G. .
Fig. 2 Lateral view of the albino rat brain weighing 1.5 grams. Enlarged 1.8 diameters. To show the position at which the height was measured. HK = Height Ht.
3. Length EF (abbreviation L.F.), passing through the frontal pole at E and running parallel to the mesial surface of the hemisphere (fig. 1).
4. Length EG (abbreviation L. G), passing from the frontal pole at E to the occipital pole at G (fig-. 1). This measurement gives the greatest length.
5. Height HK (abbreviation Ht.), from the stalk of the hypophysis to the dorsal surface and vertical to the plane on which the brain is resting (fig. 2) .
These lines here marked on the surface of a cerebrum really indicate the shortest distance between the terminal points, a distance which has been exactly measured with sliding calipers to a twentieth of millimeter.
As a matter of fact, the point G is difficult to fix, while the other points are relatively easily found and fixed. I took as G the extreme point of lateral contact of the cerebrum and the cerebellum (disregarding the paraflocculi). Sometimes this line of contact was disturbed in the removal of the brain, but in such instances I replaced the parts and measured the greatest distance from the frontal tip to a point at the occipital pole which was supposed to be G.
To measure the height, I brought the brain to the edge of the glass plate, inserted one end of the calipers under the basal surface at the stalk of the hypophysis and, holding the calipers vertically to the plate, carefully measured the distance to the dorsal surface of the brain.
In a fresh brain it is of course hard to get exact measurements owing to the softness of the brain substance, but each measurement was repeated more than three times for each diameter and the average value was recorded.
These measurements were intended first, to show the rate of increase in each dimension of the cerebrum during growth and second, to furnish a basis with which to compare the corresponding measurements after fixation for histological study and at various later stages. All these data are necessary in order to determine the coefficients needed to convert the observed values of the cortical thickness, cortical area, etc., as seen on the slide, into the values for the fresh condition of the material.
Among above diameters, the L. F was measured in the plane, from which the sagittal sections were taken for the investigations on the cortex, and the diameter W. D. in the plane from which the frontal sections were taken for the same purpose. So the diameter L. F measured in the fresh brain is comparable with the correspondng diameter in the sagittal sections and the diameter W. D with that in the frontal sections. The diameters W. B, W. D and L. G are controllable in the horizontal sections, which were taken in a plane passing through the frontal pole and approximately parallel to the basal surface of the brain. The measurements W. B, W. D and L. F were utilized as factors for correction-coefficients used to convert the cortical thickness as measured on the sections into the values for fresh condition, — as will be described in another study. The height is not controllable directly in any section prepared by me. The diameters W. B, L. G and Ht. indicate the maximum values in each dimension of the cerebrum and by them it would be possible to outline the shape of a cerebrum of the albino rat, because it is very simple in form.
These five diameters representing three dimensions of the cerebrum are therefore available for a systematic comparison of the changes which occur in the shape and size of the cerebrum during its growth.
IV. MEASUREMENTS PRESENTED IN TABLE AND CHART
Table 3 gives for each brain weight group the data obtained by measurements on fresh brains according to the above mentioned procedure. The individual measurements have been placed on file at The Wistar Institute.
Chart 1 shows graphically the linear measurements given in table 3.
V. Discussion
From the study of table 3 and chart 1, it is seen that the cerebrum of the albino rats does not increase in volume so as to maintain the proportions present at birth, but that the rates of increase differ a little in the several dimensions.
The diameter W. B. has an almost fixed rate of increase gaining a little less rapidly than the cube root of the brain weight
TABLE 3
Giving the brain weights for each brain weight group, the cube roots of the brain weights and the linear measurements for width, length and height of the cerebrum.
Albino rat
BRAIN
NTJMBEB
AVERAGE
CUBE ROOT OF
LINEAR MEASUREMENTS
WEIGHT
OF
BRAIN
THE
GKOUP
CASES
WEIGHT
BRAIN WEIGHT
W. B
W. D
L. G
l.'f
Ht.
grams
mm.
mm.
mm.
mm.
mm.
I
3
0.161
0.545
7.02
6.58
6.18
5.60
4.52
II B.
10
0.254
0.633
8.64
8.05
7.12
6.34
5.39
Ill
11
0.341
0.699
9.28
8.52
7.84
7.20
5.85
IV
10
0.424
0.750
10.02
9.11
8.50
7.92
6.35
V
19
0.544
0.816
10.78
10.02
9.41
8.69
6.93
VI
4
0.622
0.854
11.24
10.44
10.00
9.39
7.23
VII
7
0.769
0.916
12.05
11.10
11.09
10.59
7.91
VIII
10
0.845
0.945
12.26
11.48
11.43
10.88
8.22
IX
5
0.954
0.984
12.90
12.10
12.12
11.42
8.54
. X
6
1.047
1.016
13.05
12.22
12.23
12.03
8.50
XI
6
1.156
1.049
13.50
12.61
12.61
12.35
8.94
XII
6
1.253
1.078
13.79
12.99
13.04
12.50
8.93
XIII
7
1.334
1.101
13,87
13.14
13.45
13.09
9.16
XIV
5
1.449
1:132
14.04
13.42
13.77
13.31
9.25
XV
7
1.558
1.159
14.42
13.76
14.28
13.61
9.50
XVI
9
1.662
1.184
14.44
13.62
14.93
14.10
9.34
XVII
7
1.737
1.202
14.80
14.03
15.29
14.51
9.53
XVIII
5
1.832
1.224
14.88
14.22
15.47
14.63
9.68
XIX
1
1.924
1.243
14.65
14.10
16.00
15.40
9.75
XX
3
2.037
1.267
15.39
14.62
16.65
15.30
10.02
Ratios II
XX
8.02
2.00
1.78
1.81
2.34
2.41
1.86
IT Ife 15 14 13 12 11 10
/
/2
^z^
6 5
4
L_l
i
1 Q
2
3 Q
4 Q
5 Q
6 Q
r Q
8
9 I
1
1 1
2 13 14 15 Ife n 18 19 20
y.s
Chart 1 Giving for each brain weight group, in millimeters, on brain weight in grams, the values for the several diameters. W .B. and W .D., width; L.F . and L.G., length; Et., height.
• — • — • = W.B.
• •= W.D.
X-
° — ° — ° = L.G.
o o ^ Li.h .
X = Ht.
(volume) (see also table 4, column C). The approximate value of W. B can be estimated by formula (1) as follows:
W . B. (mm.) = Cw ^ vBrain weight (grams) (1)
grains
where C^ will be 13.5 for a brain weighing 0.3-0.5 13.2 for a brain weighing 0.5-1.0 12.9 for a brain weighing 1.0-1.3 12.5 for a brain weighing 1.3-1.6 12.2 for a brain weighing 1.6-2.1
The value for the measurement W. D stands in an almost fixed relation to that for W. B. The latter averages through its course 0.6 to 1.0 mm. below the former, the average difference being 0.76 mm. Thus in chart 1 both graphs run nearly parallel to each other.
The "measurement L. G increases rapidly as compared with the other diameters. The formula (2) which expresses the relation between it and the brain weight is as follows :
L. G. (mm.) = CY X vBrain weight (grams) (2)
grams where CY will be 11.2 for a brain weighing 0.3-0.5 11.5 for a brain weighing 0.5-0.7 12.2 for a brain weighing 0.7-1.6 12.7 for a brain weighing 1.6-2.0 13.1 for a brain weighing 2.0-2.1
The graph for the measurement L. F runs in general parallel to that for L. G, as might be inferred from the relation of the two diameters, but after the brain has reached the weight of 1.3 grams, the difference between them tends to increase owing to the slightly more rapid growth of L. G. The difference between L. F and L. G ranges between 0.20 and 1.35 mm. In general, the difference tends to decrease from birth (0.78 mm.) to the brain weighing 1.0 to 1.1 grams, at which stage the difference is least (0.20 to 0.26 mm.), and then increases again (up to 1.35 mm.) as the brain weight advances.
At birth the width {W. B and W. D) surpasses considerably the length (L. G and L. F) and the cerebrum is short and rounded. But very soon the length begins to increase more rapidly than the width and the shape becomes more and more elongated. The measurement L. G surpasses W. B and the measurement L. F surpasses W. D at the stage when the brain reaches 1.6 grams in weight.
The width-length index of the brain, here used, is obtained by
the formula — '- It is at birth about 127, reaches ICO
L.F
in a brain weighing 1.3 — 1.5 grams and is about 95 in old age.
The height of a brain may be obtained by the following formula (3) :
Ht. (mm.) = Ch X V Brain weight (grams) (3)
grams
where Ch will be 8.6 for a brain weighing 0.3-1.2 8.3 for a brain weighing 1.2-1.6 7.9 for a brain weighing 1.6-2.1
The increase of Ht. is somewhat more rapid than the increase in width, but is rather slow as compared with the increase in length, so that in relation to its length the brain flattens somewhat as the age advances.
If the initial values of the diameters in the newborn brain group (Group II) be taken as unity and the corresponding values of the diameters in the other successive groups be compared with these units, the series of ratios in columns D, E and F, table 4, are found. If the shape of the cerebrum remained the same throughout growth, the product oi W. B X L. G X Ht. would give the relative volume of the cerebrum at maturity as compared with its volume at birth.
As already stated, the weight of the cerebrum stands in an almost fixed relation to the weight of the entire brain, so the ratio of the total brain weight to its weight at birth would be the same as the ratio for the cerebrum and the cube root of that ratio would indicate the theoretical increase in one (mean) dimension, if the cerebrum did not change in form. These calculated ratios based on the data in table 3 are given in table 4. From among the values given in table 4, the cube root of the brain weight ratio and the ratios of W. B, L. B and Ht. are presented in chart 2 in smoothed graphs.
On examining chart 2, we see that the diameter W. B increases in an almost fixed relation to the theoretical curve denoted by ■\/C (representing the cube root of the bran weight ratios), indicating that W. B is growing almost in proportion to the increase in total volume. The graph for L. G shows the rapid growth of this dimension. The rate of increase is most rapid in brains weighing 0.25 to 0.90 grams, then, in the brains weighing 0.90 to 1.25 grams, the curve runs nearly parallel to \/C, and after that period the rate becomes more rapid again. Up to a brain weight of 1.1 grams, the increase of Ht. is nearly equal to that of \/C and after that becomes slower. Generally speaking, in the period in which the brain weighs 0.9 to 1.2 grams, the three dimensions of the cerebrum increase in nearly the same proportions, a fact to which we shall return later when considering the growth in thickness of the cerebral cortex.
If, in table 4, the brain weight ratio be compared with the ratio oi W. B x L. G X Ht. for any brain weight group, it appears that the values are nearly equal in the groups II-XII, though some fluctuations under 0.2 may be seen. But in groups beyond XII, the values in the two series deviate from one another; those for the brain weight ratios being consistently larger. This shows roughly that in the brains weighing 0.25 to 1.20 grams the volume and weight keep a fixed relation, but that in the brains weighing more than 1.2 grams the total weight increases more rapidly than the cerebral volume, as measured by the diameters which were chosen. This relation probably depends on several causes. 1. As already noted, at the beginning of the present paper, the cerebellum develops more rapidly than the other parts of the brain, attaining at maturity over thirty-four times its initial weight. This will be one of the reasons why the relative weight increase of the total brain is greater than the relative volume increase of the cerebrum only.
TABLE 4 Giving Jrom birth to matimiy the ratios of the cube root of the brain weight, ratios of W. B, of L. G and of Ht., and also the ratios of the products of these three values
A
B
C
D
E
F
G
BRAIN WEIGHT GROUP
Br&in weight
Ratio of brain weight
Cube root of the ratio
W.B
L. G.
Ht.
Ratio of
Their ratios to theinit at birth
ial values
W. BX L. GXHt.
(/rams
II
0.254
1.000
1.000
1.000
1.000
1.000
1.000
III
0.341
1.343
1.103
1.074
1.104
1.085
1.284
IV
0.424
1.669
1.186
1.160
1.194
1.178
1.631
V
0.544
2.142
1 .289
1.248
1.322
1.286
2.120
VI
0.622
2.449
1.348
1.301
1.405
1.341
2.451
VII
0.769
3.028
1.447
1.396
1.558
1.467
3.188
VIII
0.845
3.327
1.493
1.419
1.605
1.525
3.474
IX
0.954
3.756
1.554
1.493
1.703
1.584
4.026
X
1.047
4.122
1.603
1.511
1.718
1.577
4.091
XI
1.156
4.551
1.657
1.563
1.771
1.659
4.590
XII
1.253
4.933
1.702
1.596
1.832
1.657
4.843
XIII
1.334
5.252
1.738
1.606
1.889
1.700
5.154
XIV
1.449
5.705
1.787
1.625
1.934
1.716
5.393
XV
1.558
6.134
1.831
1.669
2.005
1.763
5.899
XVI
1.662
6.543
1.870
1.671
2.097
1.733
6.073
XVII
1.737
6.839
1.898
1.713
2.147
1.768
6.504
XVIII
1.832
7.213
1.932
1.722
2.173
1.796
6.720
XIX
1.924
7.575
1.964
1.696
2.247
1.809
6.893
XX
2.037
8.020
2.002
1.781
2.338
1.859
7.744
2. The specific gravity of the brain substance is probably increasing as the age advances, especially after the brain has at
L.G 55
Ht.
W.B
O 02 B af
Brain weight in qrams.
Chart 2 Showing on brain weight by smoothed graphs, the ratios of the width W.B., the length L.G. and the height Ht, as compared with the cube root of the brain weight y^ C
tained 1.2 grams in weight, for as already determined by Watson ('03) the myelination of the brain begins in the albino rat at the age of fourteen to twenty days and this process, which increases the specific gravity of the brain, continues most energetically during and after the fourth week, when the brain attains 1.2 to 1.3 grams in weight.
3. Finally it is at about this period, when the brain has reached 1.2 grams in weight, that the more rapid growth in the length appears and the change in the proportions between the lengths of the diameters which is thus brought about tends, as a mere matter of arithmetic, to make the values of their product less than it would have been had their proportions remain the unaltered.
Sex characteristics. When brains of different sexes but of like weight were compared, there was not detected any considerable sex-differences in measurements, except in three cases. These individuals had apparently an elongated form of brain, their lengths being markedly high as compared with the average values for the brains of like weight. These three were all old females, exact age unknown. ^ In other respects, even these brains, showed no peculiar characteristics.
Hatai ('07) concluded from his skull measurements of the mature albino rats that, in every respect other than the nasal bone, the female cranium might be considered as an undersized male cranium, and vice versa, since the other differences found between the two sexes were too small to be significant. This statement is probably true for the form of the cranial cavity, i.e., the form of the brain, as indicated by my measurements on brains of like weight but different sex. According to Hatai ('07) the skull capacity of the mature albino rat measured and represented by shot weight, is thus; male: 10.896 grams, female: 10.368 grams, which empirically correspond to the brains weighing 1.822 grams (male) and 1.725 grams (female) respectively, suggesting that the specific gravity of the male brain substance is slightly higher than that of the female (male 6.009: female 5.980).
- According to my observations, the brains from rats which were severely underfed for a long time and whose body weights were reduced considerably, in the younger age, not only weigh less than the brains of standard rats of like age, but have generally an elongated shape as compared with the controls.
VI. Summary
- On the fresh brain of the albino rat, five diameters were measured at fixed localities. By these the shape and the size of the cerebrum can be indicated and by the changes in them, the postnatal growth can be studied. As material 141 albino rats at every stage of growth were used.
- The greatest width (W.B), the greatest length (L.G) and the height (Ht.) of the cerebrum at birth are respectively 8.6, 7.1 and 5.4 mm. The same measurements at full maturity are respectively 15.4, 16.7 and 10.0 mm. (table 3). The ratio of each measurement in the mature brain to its initial value at birth is, therefore, respectively 1.78, 2.34 and 1.86. Using the product of these three diameters as a measure the ratio of volume of the mature cerebrum to the volume at birth is 7.74.
- The increase in the ratio of the weight of a cerebrum according to age is quite equal to the increase in the ratio of total weight of the brain, which includes the cerebellum, the stem and the olfactory bulbs, besides the cerebrum. Thus the developmental stage of the cerebrum (in weight) corresponds to the developmental stage of the entire brain (in weight).
- As the cerebrum increases its volume with age, it does not enlarge proportionally in all dimensions. In general, the length increases most rapidly while the width and height increase more slowly. However, in the period between the tenth and the twentieth day after birth (brain weight 0.95 to 1.2 grams), the cerebrum is enlarging in volume quite uniformly in all its dimensions.
- In the newborn cerebrum the width is greater than the length (width-length index, ^127). After birth, the increase in the longitudinal diameter surpasses that of the transverse diameter and finally at full maturity the cerebrum has a somewhat elongated form (width-length index 95).
- Sex differences in the size and shape of the cerebrum are not significant, when brains of like weight are compared.
- A rough estimation indicates that the specific gravity of the brain increases after brain has attained 1.2 grams in weight. This is due probably to myelination.
References
Donaldson, H. H. 1915 The Rat. Memoirs of The Wistar Institute of Anatomy and Biology. No. 6.
Hatai, Shinkishi 1907 Studies on the variation and correlation of skull measurements in both sexes of mature albino rats (Mus norvegicus var. albus). Am. Jour. Anat., vol. 7, pp. 423-^1.
Watson, J. B. 1903 Animal education. Con. from, the Psychol. Lab. Univ. of Chicago, vol. 4, No. 2, pp. 5-122.
Cite this page: Hill, M.A. (2024, April 23) Embryology Paper - Comparative studies on the growth of the cerebral cortex 1 (1917). Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Paper_-_Comparative_studies_on_the_growth_of_the_cerebral_cortex_1_(1917)
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