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Morphogenetic studies of the rabbit. XX. A comparison of the weights of the brain and of its parts in a large and in a small sized race of rabbits

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MORPHOGENETIC STUDIES O F T H E RABBIT
XX. A COMPARISON O F T H E WEIGHTS O F T H E BRAIN AND
O F I T S PARTS I N A LARGE AND I N A SMALL
SIZED RACE O F RABBITS
HOMER B. L A T I M E R AND P A U L B. SAWIN'
Department of Anatomy, University of Kansas and
Roscoe B. Jackson Memorial Laboratory, B a r Harbor, Maine
The weight of the brain and its relation to body weight and
to stature has been an interesting subject of investigation for
over a century, and in 1892 Marshall reported the weights of
the parts of the human brain. Some of this literature, especially on the weights of the parts of the brain in man and in
animals has been reviewed in an earlier publication (Latimer
and Sawin, '55c). The weights of the parts of the brain in
several species of vertebrates have been compared (Latimer,
'SS), but so far as is known no study has been made on the
weights of the parts of the brain in closely related groups of
differing body size. A recent report shows that all of the
internal organs do not have the same percentages of total body
weight in rabbits of large race I11 and small race X (Latimer
and Sawin, '57).
The weights of the parts of the brain in small race X rabbits have been reported (Latimer and Sawin, '55c) ; and this
study will present the weights and relative weights of the
parts of the brain in large race I11 rabbits, and then compare
these weights with those in rabbits of small race X.
MATERIALS A N D METHODS
The 35 male and 30 female rabbits of large inbred race 111,
developed from the New Zealand White rabbits are described
'Aided by a grant from the American Cancer Society and f r o m the Kationnl
Caiiccr Institute, National Institutes of Health, United States Public Health
Service.
619
620
HOMER B. LATIMER AND PAUL B. SAWIN
in a recent publication (Latimer and Sawin, ’57). The 100
rabbits of small race X, descended from Castle’s small race are
likewise described in an earlier report (Latimer and Sawin,
%a). Although race X carries the dwarf gene and some of
the race X rabbits were heteroxygous dwarfs (Latimer and
Sawin, ’55b), 35 males and 30 females were normal, or without the dwarf characteristics and only these normal, or nondwarf rabbits of race X will be used for comparison with
race I11 rabbits. Throughout this report these normal rabbits
of race X will be referred to as “race X rabbits.” The
weights of the parts of the brain of the smaller race X rabbits
are presented in the previous report (Latimer and Sawin,
’55c) and will not be repeated here.
Both races of rabbits were raised at the R. B. Jackson Rlemorial Laboratory in Bar Harbor, Maine, during approximately the same time. They were shipped to Kansas and
studied in one continuous series. The methods of dividing the
brain are the same f o r all of these rabbits and are the same
as the methods used for studies of cat and dog brains (Latimer,
’38). All of the dissections were made by one person (H. B. L.).
Weights and percevztnge weights
The weights in grams of the brain, of its 4 divisions and of
the spinal cord of race I11 rabbits are shown in panel A of
table 1. The weights, standard deviations and coefficients of
variation for the males are listed in the first three columns
and the next three columns present similar data for the females. The last column contains the “ t ” values of the differences between the sexes, with the sex having the larger
value indicated. All but two of these weights (cord and
mesencephalon) are heavier, but not significantly heavier in
the males. The spinal cord is slightly heavier in the females
and thus resembles the total body weight which is significantly
heavier at the 5% level in the females.
The weight of the brain, of its 4 parts and the weight of the
cord are all more variable in the females, while the gross
~
49.37
67.13
7.95
14.95
9.98
5.54
9.20
6.11
7.14
6.08
6.16
Weights in grams
11.557
5.940
7.745
0.931
1.737
1.144
11.35
9.37
11.90
11.18
11.53
10.57
0.403
0.206
0.270
0.0324
0.0605
0.0398
3.47
0.89
0.40
0.60
0.45
~
7.03
1.33
5.01
4.03
4.50
51.47
67.00
8.05
15.04
9.90
Pancl C Weights as percentages of brain weight
0.048
0.019
0.033
0.0037
0.0072
0.0044
4.41
1.25
0.52
0.84
0.53
0.041
0.019
0.030
0.0035
0.0062
0.0041
0.740
0.551
0.550
0.084
0.121
0.091
‘ “ t ” values of 2.04 and above are signscant at 5% and 2.75 and above are significant a t 1%.
Spinal cord
Prosencephalon
Mesencephalon
Cerebellum
Medulla
0.419
0.205
0.281
0.0332
0.0626
0.0417
Brain
Spinal cord
Prosencephalon
Mesencephalon
Cerebellum
Medulla
0.649
0.532
0.481
0.066
0.106
0.072
Panel A
Stand.
dev.
Average
Panel B Weights as percentages of net body weight
11.711
5.781
7.863
0.931
1.750
1.167
Brain
Spinal cord
Prosencephalon
Mesencephalon
Cerebellum
Medulla
Average
F EM A LES
Coef.
var.
MALES
Stand.
dev.
8.57
1.86
6.46
5.58
5.35
10.21
9.17
11.03
10.84
10.33
10.22
6.40
9.28
7.10
8.98
6.95
7.98
Coef.
var.
Weights and percentage weights of the brain and o f i t s parts and o f the spinal cord in 35 male and
30 fsniale rabbits of race III
TABLE 1
0
2.12
1.42
0.12
1.39
0.87
1.25
1.77
0.88
1.16
0.92
0.00
0.45
1.12
1
8 0.48
0 0.91
0 0.53
8 0.59
8
8
8
d
d
8
d
t
I‘ 9 ,
W
E
B
id
622
H O M E R B. L A T I M E R A N D PAUL B. SAWI'IN
body weight is more variable in the males (Latimer and
Sawin, '57).
The same 6 parts of the central nervous system as percentages of net body weight are shown in panel B,table 1. The
net body weight is the weight of the rabbit immediately after
anesthetization minus the weight of the contents of the digestive tube and all fat which could be removed by gross dissection. This net body weight better represents the living animal
than the gross body weight. The brain and its 4 parts not
only are heavier (panel A ) but they also form larger percentages of net body weight in the males. The weight and percentage weight of the spinal cord however, are more like
the body weight and thus heavier in weight and in percentage
weight in the females.
Although the weights of all parts of the central nervous
system in panel A are more variable in the females, these same
parts as percentages of net body weight in panel B are slightly
more variable in the males. Since the net body weight of the
males is more variable, changing the weights in grams to percentages of this more variable body weight evidently causes
this greater variability in the percentages of the parts of the
male central nervous system. These percentages in both sexes
in panel B are more variable than the weights in panel A.
Panel C of table 1 presents the weights of the spinal cord
and of the 4 parts of the brain as percentages of the weight
of the entire brain. The spinal cord is about half the weight
of the entire brain in these race I11 rabbits and it is the only
part of the central nervous system in this entire table with a
significant sex difference. Seventeen of the 29 measurements
of the parts and organs of these race I11 rabbits in table 1
of the preceding publication (Latimer and Sawin, '57) show
a significant sex difference and most of them were heavier in
the females. While there are some slight sex differences in
the weights and percentage weights of the parts of the brain,
none of them is significant. Possibly the general pattern of
the brain is developed so early in the embryonic period that
it is not affected by the later appearing sex characteristics.
BRAIN I N LARGE AND SMALL RABBITS
623
The brain also appears to be quantitatively more or less independent of the weight of the entire body. This will be evident
in the correlations between body weight and brain weight,
none of which is significant.
I n panel C, as well as in panel A, the parts of the central
nervous system are more variable in the females. The more
variable body weight of the males causes the greater variability of these parts of the nervous system when expressed
as percentages of the body weight in panel B.
Correlations
The correlation coefficients between the body weight and
body length and the various parts of the central nervous system and also the correlations betmeen the parts of the nervous
system are shown in table 2. I n these race I11 rabbits, as has
been found in race X rabbits, the females have, in general,
higher correlation coefficients than the males. The coefficients
of correlation between the weight of the brain and its 4 parts
in both male and female rabbits are all significant at the 1%
level. The net body weight is significantly correlated at the
1% level in the males, with the medulla and spinal cord only,
and in the females with only the weight of the spinal cord.
I n neither sex are the net body weights and the weights of the
brain significantly correlated.
The coefficients of correlation in the males range from
0.976, the highest correlation in the table, to - 0.235, and
0.105. There are
in the females the range is from 0.969 to
5 coefficients of correlation in the males which are negative.
All of these are with the length of the spinal cord and all are
too low to be significant. No negative correlation coefficients
are found in the females. I n the males there are 15 coefficients
of correlation not significant at the 5% level and in the females,
but 8. There is but one correlation in each sex above 0.9 and
this is between the weight of the entire brain and the prosencephalon. The prosencephalon forms over two-thirds of the
total brain weight and hence these high correlations are to be
expected.
+
+
+
TABLE 2
nevvou.9 system
0.812
0.317
0.655
0.194
0.224
0.391
0.274
0.474
Body L.
Brain
Cord wt.
Cord L.
Prosen.
Mesenceph.
Cerebellum
Medulla
Body wt.
NET
BODY
WT.
0.418
0.173
0.472
0.124
-0.097
0.528
0.246
0.666
BODY
LENGTH
0.702
0.759
0.732
0.976
-0.172
0.792
0.692
0.177
BRlIN
0.692
0.310
0.645
0.585
0.218
0.446
0.811
0.476
.
CORD
WT
-0.002
-0.054
O.li9
-0.235
0.672
0.231
0.752
0.887
L:zgH
0.599
0.663
0.626
0.132
0.324
0.969
0.572
0.105
PROSEN.
0.708
0.533
0.591
0.340
0.474
0.698
0.613
0.241
MESEN.
0.468
0.518
0.501
0.368
0.543
0.664
0.750
0.235
B~~~~~
0.581
0.498
0.620
0.280
0.509
0.735
0.615
0.266
MEDULLA
All correlations are positive except those otherwise marked. Male correlations are in the lower left part and the female
correlations, in the upper and right pa r t of table. Correlations in the males of 0.325 and above are significant at 5% and correlations of 0.418 and above are significant at 1%. Similar values for the felnales are 0.349 and 0.449 respectively.
Coefficients of correlation with the central
BRAIN I N LARGE AND SMALL RABBITS
625
The central nervous system and its parts are more variable
in weight in the females (panel A of table l), yet the correlations between the parts of the central nervous system are
higher in the females. Thus the quantitative relationships
are more constant in the female brains than in the males.
Comparison of races III and X
The data in table 1 for large race I11 rabbits will be compared with the similar data for small race X rabbits. A
comparison of the weights of corresponding parts of the
central nervous system in the two races shows, as expected,
that all of the 6 parts of the central nervous system are heavier
in the large race I11 rabbits. They are not uniformly heavier,
however, for the percentages in race I11 males range from
124% to 146% of the weight of the similar parts of the nervous system in race X male rabbits. These percentages for
the females range from 116% to 131%. The greatest difference is for the weight of the spinal cord which has a percentage of 146.5 in the males and 130.9 in the females. The
mesencephalon shows the least difference in the males or
124.0% and in the females, the lowest percentages are, 115.6
for the cerebellum and 115.8 for the mesencephalon. The
average of these percentages in the males is 129.6 and in the
females, 120.2. All of these parts of the central nervous system
in the two races differ less than the gross body weights. The
body weight of race I11 males averages 170% of that of race
X males and the comparable percentage for the females is
144%.
There is also a sex difference in the weights of the parts
of the central nervous system. The weight of the brain and
its 4 parts are heavier in the males of race I11 and heavier
in the females of race X rabbits. The spinal cord is heavier
in the females of both races.
Panel A of table 3 presents the percentages of net body
weight of these parts of the central nervous system in race
I11 rabbits as percentages of similar relative weights of the
626
HOMER B. LATIMER AND PAUL B. SAWIN
same parts in race X rabbits of the same sex. For example,
the relative weight of the brain in the males of race I11 is
73.4% of the relative weight of the brain in race X males.
The “ t ” values in the last column are for the differences in
the percentage weights and indicate that the brain and its
TABLE 3
Weights of the parts relative t o net body weight in panel A and t o total brain
weight in panel B in race III rabbits as percentages of the same
relative weights in race X rabbits of the same sex
The “ t ” values show the significance of the differences between the weights
as percentages of net body weight or of total brain weight in the two races.
-
MALES
% ofX
race
Panel A
Brain
Spinal cord
Prosencephalon
Mesencephalon
Cerebellum
Medulla
Spinal cord
Prosencephalon
Mesencephalon
Cerebellum
Medulla
Percentages of
73.4
85.5
73.6
71.9
72.4
75.7
FIXALES
“t”
net body weight
10.41
6.95
9.81
9.94
10.10
10.51
of
race X
qo
I‘
t
9,
1
80.0
88.4
80.4
78.3
78.1
81.7
7.75
5.08
6.83
8.96
9.59
7.41
Panel B Percentages of total brain weight
7.75
110.6
115.9
100.2
0.35
100.5
97.9
1.34
97.6
98.6
1.16
97.6
102.9
1.95
102.1
4.86
1.08
1.44
1.89
1.40
l(( t ” values in the males of 2.03 and above are significant a t 5% and 2.72 and
above are significant a t 1%. Similar valucs f o r the females are respectively, 2.04
and 2.75.
parts and the spinal cord are all significantly lighter, relative
to net body weight, in the larger race. These ratios are not all
alike however, for they range from 72% to 86% for the male
rabbits and from 80% to 88% for the females.
All of the percentages in panel A, table 3 are relatively
smaller in the large race I11 rabbits. This is as expected, for
it is generally accepted that the larger of two closely related
races has the relatively smaller brain and spinal cord. May
BRAIN I N LARGE AND SMALL RABBITS
627
this be accounted for, at least in part, by the longer postnatal
growth period in the larger race of rabbits, which gives the
general body weight more time to increase after the precocious
nervous system has completed its growth? The weights of
the heads of these two races of rabbits show this same difference. The relative weight of the head of race I11 males is
89% of the relative weight of the head in raee X males and
the ratio f o r the females is 90%. 9recent study of the human
skeletons of a small sized Asiatic race shows a relatively
larger skull (Lowrance and Latimer, '57). The skulls of these
Asiatic skeletons average 78% of the skull weight in an
American series of skeletons, while the weights of the long
bones of the extremities average from 50% to 60% of the
weights of the same bones in the larger American skeletons.
These Asiatic people, like the small race X rabbits, mature
more rapidly and their heads and brains as well, are relatively
larger than in a larger and more slowly maturing race.
The percentages in panel A , table 3, show that the 6 parts
of the central nervous system are more alike in the females
of the two races than in the males, but it must be remembered
that there is less difference in the body weights of the females
than in the males of races I11 and X rabbits, and thus these
parts of the central nervous system are more o r less in
accord with the difference in body weight in the two sexes.
The percentages of 86 and 88 for the spinal cord of the males
and females, respectively, show that the cord has less difference in the two races than is found in the brain o r in any of
its parts. Another factor affecting the weight of the cord is
the greater body length in race I11 rabbits. The index of body
build shows that race I11 rabbits of both sexes are relatively
longer bodied than race X rabbits (Latimer and Sawin, '57).
Following the cord, which has the least difference in percentage weights is the medulla with percentages of 76 and 82 for
the males and females. This may be explained by the fact that
the medulla oblongata is the anterior continuation of the
medulla spinalis, both structurally and functionally, and hence
it, like the spinal cord, conforms more closely to the greater
628
HOMER B. LATIMER AND PAUL B. SAWIN
body size in race I11 rabbits. The percentages of the entire
brain and the three remaining parts of the brain show a
variation of but about 2% in both sexes and hence we may
conclude that these parts retain nearly the same relative
proportions in both races of rabbits.
Panel B of table 3 presents the weights of the spinal cord
and the 4 parts of the brain, relative to weight of the entire
brain of race I11 rabbits, as percentages of the corresponding
weights relative to total brain weight in race X rabbits of the
same sex. The percentages and the “ t ” values of the differences for the males are shown in the first two columns and
similar data for the females, in the last two columns. The
spinal cord of both sexes is the only part of the central nervous
system showing a significant percentage difference. The spinal
cord is 49.4% of the brain weight in the males of race I11 and
51.5% in the females. The corresponding percentages in race
X rabbits are: 42.6% and 46.5% respectively. Thus the cord
is significantly larger relative t o brain weight in the large
rabbits, again showing that the weight of the spinal cord
resembles the body weight more than the brain weight. The
relative weights of the 4 divisions of the brain are not significantly different in the two races. The prosencephalon and
medulla are slightly larger in race I11 but these differences
in both sexes are not significant. I n the earlier study of the
normal and dwarf rabbits of race X, it was shown that the
prosencephalon was slightly but not significantly larger in
the normal than in the dwarf rabbits of race X.
The data for the rabbits of large race I11 and for both the
normal and dwarf rabbits of small race X seem to indicate
that the relative weights of the parts of the brain in both
sexes remain rather constant, or the rabbit brain is uniformly
proportioned as far as the weights of these 4 divisions are
concerned, although the relationships of brain and body weight
are affected by the size of the rabbit.
Although the proportions of the brain itself are very similar
in both races, there are certain tendencies which may be mentioned. The relative weights of the prosencephalon and me-
BRAIN I N LARGE AND SMALL RABBITS
629
dulla of race I11 rabbits (panel C, table 1)are slightly larger
in the males and the other two parts correspondingly smaller.
This is likewise true for race X rabbits except that the medulla comprises 9.7% of the total brain weight in each sex.
The relatively larger cerebellum in the heavier females of both
races is in accord with the suggestion of Larsell and von Berthelsdorf ( '41) that the cerebellum tends to parallel the weight
of the musculature. I n both sexes of the large race I11 rabbits,
the cerebellum is relatively smaller than in the small rabbits
of race X, but the weight of the musculature relative to body
weight in race I11 rabbits is 94% and 92% of the relative
weight of the musculature of race X rabbits of the same sex.
There is a difference in the variability of the weights of the
parts of the central nervous system in the two races. I n race
I11 the weights in grams and also the percentages of total
brain weight are all more variable in the females, while the
corresponding parts are, in general, more variable in the
males of race X rabbits.
Empirical formulae
Another difference between the brains of race I11 and race
X rabbits is made apparent through application of the empirical formulae. The formulae listed in table 8 (Latimer and
Sawin, '55c) for race X rabbit brains and which gave estimated
values differing from the observed weights by from 1.64%
to 2.09% did not fit these race I11 rabbits. The percentage
differences f o r the race I11 rabbits ranged from 6.52% to
12.98%. Some of the cephalization formulae from the literature gave better estimates of brain weight for race I11 than
for race X rabbits. The formula of Quiring ('41) gave better
estimates of brain weight in race I11 than it did for race X
rabbits. The percentage differences between the observed
and the calculated values for race I11 were 5.81% for the
males and 0.82% for the females. Quiring's formula appears
to fit the females of both races better than the males.
630
HOMER B. LATIMER AND PAUL B. SAWIN
The brains of large race I11 rabbits as percentages of body
weight are more like the percentages given by Crile and
Quiring ('40) and Levine et al. ('47) than the percentage
weights of small race X rabbits. Levine's rabbits were New
Zealand Whites.
The use of these cephalization formulae in the study of these
two races of rabbits indicates that size, or body weight of the
rabbit has much to do with their accuracy in predicting brain
weight. These formulae will not predict brain weight with
equal accuracy for both large and small rabbits.
SUMMARY
The body weight of the males of large race I11 rabbits averages 170% of the body weight in small race X males. The
similar percentage for the females is, 144%. All of the parts
of the central nervous system are not uniformly heavier in
the large race I11 than in small race X rabbits. These ratios
range from 124% to 1467, f o r the males and from 116% to
131% f o r the females. The brain and its 4 parts are heavier
in the males of race I11 and heavier in the females of race X.
The cord is heavier in the females of both races.
I n both races, the weights of the parts of the central nervous system as percentages of body weight are more variable
than the weights in grams. The parts of the brain are least
variable when expressed as percentages of the weight of the
entire brain.
The parts of the brain as percentages of total brain weight
are very much alike in the two races. The prosencephalon
forms approximately 67% ; the cercbcllum, 15% ; the medulla,
10% ; and the mesencephalon, 8%. The prosencephalon and
medulla are slightly larger relatively in the males.
The spinal cord of race I11 is 4970 of the weight of the brain
in the males and 52% in the females. Similar percentages for
race X rabbits are: 437% and 46%.
The empirical formulae developed for race X rabbits do not
give as good estimated values for the brain weights of race
BRAIN I N LARGE AND SMALL RABBITS
631
111. The cephalization formulae from the literature give
better estimates of brain weight for race I11 than for race X
rabbits. The accuracy of these formulae seems t o depend on
body weight of the rabbit.
Although the central nervous system is more variable in
weight in the female, the coefficients of correlation between the
parts of the system are, in general, higher in the females.
LITERATURE CITED
D. P. QUIRING 1940 A record of the body weight and certain
organ and gland weights of 3690 animals. Ohio J . Sci., 40: 219-259.
LARSELL,
O., A N D S. VON BERTHELSDORF
1941 The ansoparamedian lobule of
the cerebellum and its correlation with the limb-muscle masses. J. Comp.
Neur., 75: 315-340.
LATIMER,
H. B. 1938 The prenatal growth of the cat. VII. The growth of the
brain and of its parts, of the spinal cord and of the eyeballs. Ihid.,
68: 381-394.
1956 The weights of the parts of the brain i n several species of
animals. Trans. Kans. Acad. Sci., 59: 432-441.
LATIMER,
H. B., AKD P. 13. SAWIN 1955a Norphogenctic studies of the rabbit.
X I I . Organ size i n relation to body weights in adults of small race X.
Aaat. Rec., 12.3: 81-102.
l955b Morphogenetic studies of the rabbit. XTII. The influence
of the dwarf gene upon organ size and variability in race X. Jhid.,
123: 447-466.
1955c The weight of the brain, of its parts and the >\?right and
length of the spinal cord in the rabbit (race X ) . J. Comp. Xcur., 103:
513-540.
1957 Morphogenetic studies of the rabbit. X I X . Organ size in
relation to body size in large race 111 and in small race X. Anat. lter.,
1 2 9 : 457-472.
LEVINE,c. J.. W. MA",
H. C. HODGE,
I. ARIELAND 0. DUPONT 1941 Distribution of body weight in the organs and tissues of the rabbit. Proc. SOC.
Exp. Biol. Me&, 47: 318-321.
LOWRANCE,
E. W., AND H. B. I A T I h I E R 1957 Weights and measurements of
105 human skeletons from Asia. Am. J. Anat., 1 0 1 : 445-459.
MARSHALL,
J. 1892 On the relations between the weight of the brain and i t s
parts, and the stature and mass of the body i n man. J. Anat. Physiol.,
36: 445-500.
QUIRING,D. P. 1941 The scale of being according to the power formula. Growth,
5: 301-327.
CRILE, G.,
AND
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