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Corpus callosum in sexually dimorphic and nondimorphic primates.

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AMERICAN JOURNAL, OF PHYSICAL ANTHROPOLOGY 87:349-357 (1992)
Corpus Callosum in Sexually Dimorphic and
Nondimorphic Primates
RALPH L. HOLLOWAY AND PETER HEILBRONER
Department of Anthropology, Columbia University,
New York, New York 10027
KEY WORDS
Brain, Corpus callosum, Sexual dimorphism, Cerebral lateralization, Primates
ABSTRACT
The midsagittal area and other morphological measures were
taken on the corpus callosum of four different species of primate: Macaca
mulatta, M. fascicularis, Callithrixjacchus, and Saguinus oedipus. The first
two species are strongly dimorphic, whereas the New World forms show little
dimorphism with regard to overall body size, canines, and brain weight.
Neither total corpus callosal area (TOTALCC), or other parts of the corpus
callosum (CC) showed any significant sexual dimorphism in any of the primate
species sampled. Only in M . mulatta did a sexual dimorphism appear to be
significant. In males of this species, the dorsoventral width of the splenium
was larger than in females. In addition, the anterior commissure (ANTCOMM)
evinced no sexual dimorphism in the different species.
Brain weight was significantly dimorphic in only M. mulatta, and when
ratio data were used to correct for brain weight, no significant differences were
found in the corpus callosum. This is in contrast to Homo sapiens, where the
relative size of the CC has been reported to be larger in females, and
particularly so in the posterior, or splenial portion of the CC. Correlation
coefficients were calculated for the various variables within each species. In
general, most of the callosal measures are significantly inter-correlated,
although the exact pattern varies for each species.
Thus, unlike Homo sapiens, or pongids such a s Gorilla and Pan, neither New
nor Old World monkeys show any striking evidence for sexual dimorphism in
the corpus callosum.
In recent years, a number of investigators
(e.g., de LaCoste-Utamsing and Holloway,
1982; Holloway et al.; 1986, Kertesz et al.,
1987; Demeter et al., 1988) have examined
the anatomy of the corpus callosum (CC), the
large fiber bundle interconnecting the two
cerebral hemispheres in the human brain.
(For details regarding fiber distributions see
Pandya e t al., 1971; and Seltzer and Pandya
1983.) In two of the human studies, significant sex differences have been reported for
the midsagittal sectional area of the CC, and
its splenial portion, in particular (de LaCoste-Utamsing and Holloway, 1982; and
Holloway et al., 1986; Holloway, 1990). (It is
the splenial portion that carries the fibers
interconnecting the parietal, occipital, and a
small portion of the temporal cortex. The
@
1992 WILEY-LISS, INC.
rostrum and genu contain fibers mostly related to the frontal cortex.) Although the
existence of this dimorphism has recently
been contested (e.g., Kertesz et al., 1987,
Demeter et al., 1988, Witelson, 1985, Witelson and Kigar, 1987, Byne et al., 1988, Weber and Weis, 1986), sexual dimorphism in
this non-reproductive area of the brain remains a potentially intriguing correlate of
some of the sex differences in human cerebral lateralization that have been reported
(e.g., Harris, 1978; McGlone, 1980; Kimura,
1983; Kimura and Harshman, 1984). All of
Received November 12,1990; accepted July 23,1991.
Address reprint requests to Dr. Ralph L. Holloway, Dept. of
Anthropology, Columbia University New York, NY 10027.
350
R.L. HOLLOWAY AND P. HEILBRONER
the above studies on the human corpus callosum have failed to properly take human
brain size into consideration, thus ignoring
the possibility that relative differences in
corpus callosal size will favor the female, as
originally suggested by de Lacoste-Uitamsing and Holloway, (1982). This matter has
been reviewed elsewhere (Holloway, 1990).
In nonhuman primates, which appear to
exhibit less lateralized brains than humans
(Holloway and de Lacoste-Utamsing, 1982;
Heilbroner and Holloway, 1988, 1989; Falk
19861, the possibility of sexual dimorphism
in the morphology of the CC has only recently been investigated. de Lacoste and
Woodward (1988) have examined the CC in
brain samples representing major taxonomic groups within the Primates. Their
evidence suggests greater mean total crosssectional callosal area in female than male
brains in two of these groups (pongids and
strepsirrhines), as well a s greater dorsoventral splenial width in female pongids than in
males. In contrast, these workers did not
find any sex differences in cercopithecoid or
ceboid brain samples. Unfortunately, it is
not clear from their sample of 34 primate
species (54 brains) just how many males and
females were studied within the pongids.
Their Table I11 (p. 320) indicates only that
the total number of pongids was 15,and thus
one cannot be certain how strong or weak the
within-species dimorphism was (e.g., for gorilla or chimpanzee).
In almost all studies mentioned above,
sample sizes have been rather small, and
given the controversial aspects of some of
these studies, particularly in Homo, replication studies using larger samples and as
many different species as possible seem in
order. In the present study, we attempt to
assess the degree of sexual dimorphism in
the cross-sectional area of the CC and anterior commissure (ANTCOMM) in four nonhuman primate species. These species, two
each from Old and New World monkey
groups respectively, were chosen for the contrasting patterns of anatomical and behavioral sexual dimorphism which they represent. Two of the species (Callithrixjacchus
and Saguinus oedipus) exhibit little sexual
dimorphism in either reproductive anatomy
or in behavior (Herskovitz, 1977); the other
two species, Macaca mulatta and M. fascicuZaris, exhibit anatomical sexual dimorphism
in body size and canine development, and are
also behaviorally sexually dimorphic with
respect to infant care roles, mating strate-
gies, group defense, and other social parameters (Roonwal and Monot, 1977).
In addition, it has been hypothesized by
Holloway (1983) that human sexual dimorphism in the corpus callosum may be a species-specific dimorphism related to evolutionary forces acting upon a complemental
social behavioral set of strategies, and thus
a n evolutionary residuum with less importance today than in the past. In essence, it
was hypothesized that the lower degree of
asymmetry in the female cerebral cortex
would be supported by a morphological pattern that showed a larger splenial portion in
the female brain, signifying a n increase in
fibers communicating between the two cerebral sides, particularly in the posterior parietal region. Testing this speculation must
involve the study of numerous primate and
other animal species, as well a s larger samples within Homo and the pongids. This
study is intended to add to our growing
knowledge regarding the organization of primate brains.
MATERIALS AND METHODS
The brain materials for Macaca mulatta
and M . fascicularis were kindly provided by
the New England Regional Primate Center,
the Bowman-Gray School of Medicine, N.
Carolina, the Oregon Regional Primate Center, Oregon, and the Wisconsin Regional Primate Center as described in Table 1 of Heilbroner and Holloway (1989). The brains af
Callithrix jacchus and Saguinus oedipus
were received from Oak Ridge Associated
Universities, and were removed from freshfrozen crania that had been shipped express
from Oak Ridge, Tennessee.
All brains examined were immersionfixed specimens from adult or older juvenile
monkeys from these four species with no
history of neuropathology or cerebrovascular
disease. Relatively large brain samples were
used in this study: 23 (10 males, 13 females)
Macaca mulatta 29 (16 males, 13fema1es)M.
fascicularis; 17 (10 males, 7 females) CalZithrix jacchus; 21 (11 males, 10 females)
Saguinus oedipus.
Each brain was weighed to the nearest
gram and then sectioned along the midsagittal plane. The cerebral hemisphere in which
the CC and ANTCOMM appeared to be in
the best condition was placed on a level
platform with the medial surface facing up.
Modelling clay was placed under the lateral
surface of the hemisphere to level the medial
surface. A millimeter ruler was placed along-
SEXUAL DIMORPHISM IN PRIMATE CORPUS CALLOSUM
side the hemisphere at the height of the
medial surface. An Olympus 35 mm camera
(with macrolens adapter), mounted on a tripod, fixed at a constant height for all of the
brains, was positioned directly above the
hemisphere and ruler. The camera back was
leveled, and the camera was positioned so
that the body of the CC appeared in the
center of the focusing window in the viewfinder. A color slide photograph was then
taken.
The slides were projected onto 8” x 11”
paper with a darkroom enlarger. The greatest enlargement possible ( 3 ~ - 1 0x), (depending on brain size) that permitted clear
tracing of the CC outline was used. Two
marks were made on the projection paper
indicating one centimeter on the ruler in the
photograph to denote scale. The perimeters
of the CC and ANTCOMM were then traced
onto the paper by hand from each slide.
As the corpus callosum is a single continuous structure, it is necessary to divide the CC
into somewhat arbitrary divisions that permit measurement of its various sections,
such as the rostrum, genu, body, and splenium. These divisions and the rationale for
using them have been spelled out in detail
elsewhere (e.g., de Lacoste-Utamsing and
Holloway, 1982). I n brief, following Figure 1,
we divide the corpus callosum into fifths
along a n anterior-posterior axis from rostrum through splenium. The posterior fifth
thus approximates the whole of the splenial
portion of the CC. From previous studies (de
Lacoste-Utamsing and Holloway, 19821, we
ANT CC
351
have not found any differences in the anterior % of the CC, thus we lump together the
rostrum, genu, and a part of the body of the
CC into the first Y2, or ANTCC (see Figure 1).
On each tracing, the CC is divided as follows:
first, a straight line was drawn connecting
the most caudal and rostral points on the
border of the CC. The midpoint, the most
caudal fifth (POST5AREA), and the next-tomost caudal fifth of this line were determined with vernier calipers and marked.
Line segments perpendicular to the line
were drawn from these three points to subdivide the CC into anterior and posterior
halves (ANTCC and POSTCC), and to indicate the most posterior fifth (POST5AREA
or splenium) and next-to-most posterior fifth
(NEXTAREA). We include this region, a s it
might contain some of the most anterior part
of the splenium along with the posterior part
of the body.
The area of each of these subdivisions (see
Figure 1) and the area of the ANTCOMM
were then determined using a Tamaya
Planix-2 rolling digital planimeter. Each
planimetric measurement was repeated
three times and the results averaged for each
specimen, using the mean value for our statistical calculations. In addition, splenial
width (greatest dorsoventral distance across
the splenium perpendicular to the main axis
of this region of the CC) was measured using
vernier calipers.
The SPSSX (Statistical Package for the
Social Sciences) was used for the statistical
analyses of these data. Student t-tests and
POST CC
POST 5
Fig. 1. A schematic diagram of primate corpus callosum which is the major fibrous interconnection between the
two cerebral hemispheres. The splenial portion is the posterior section toward the right; the g e m and rostrum are
anterior and to the left. The dashed lines represent the approximate transect, at right angles to the axis of the
splenium, along which dorsoventral splenial width is measured. The anterior ccmmissure (ANTCOMM) is just
slightly posterior to the pointed end of the rostral part of the corpus callosum, and given its very small size, is not
drawn on this diagram. The divisions shown in this diagram are as described in the Methods sections.
352
R.L. HOLLOWAY AND P. HEILBRONER
ANOVA subroutines were used in the analyses of the sex differences. For ANOVA, F-ratios for brain weight (Fbr) and sex (Fsx) were
calculated to determine the degree of sexual
dimorphism resulting from allometric and
nonallometric factors. In these calculations,
the callosal variable was treated a s the dependent variable, brain weight as a eovariate, and sex as the main factor.
Because there have been indications from
previous publications of a relative sexual
dimorphism (i.e., relative to brain size in
some CC measurements), ratio data were
also tested using t-tests (Ratiol-Ratio5, see
below), and ANOVA was also used on Ratio4,
as it did not contain brain weight a s a variable.
Ratiol is total CC area divided by brain
weight raised to the exponent of .66, a s this
approaches a n areal dimension more commensurate with CC area. Ratio2 is the splenial area (POST5AREA) divided by the .66
power of brain weight. Ratio3 is splenial
width divided by the .33 power of brain
weight (commensurate with a linear dimen-
sion). Ratio4 is the POSTSAREA divided by
TOTALCC area, and Ratio5 is RATIO4 divided by brain weight raised to the .66
power. In fact, simply using brain weight
provides essentially the same statistical patterns. We are using exponential values of
brain weight to keep mensurational consistency.
Finally, correlation analyses were run for
each of the species to show the relationship
between the measurements of the corpus
callosum and brain weight.
RESULTS
Few sex differences in the cross-sectional
area of these callosal subdivisions were revealed (see Tables 1 4 ) . The differences
found appear in both species of Macaca and
show greater callosal areas in males, reflecting brain weight a s shown in the ANOVA
analyses. In Macaca mulatta, however, splenial width showed a significant size difference in terms of sex, favoring males. The
posterior fifth, or splenial area, did not show
TABLE 1. Macaca fascicularis'
Region
TotalCC
AntCC
PostCC
Next 115
Sex
N
Area2
s.d.
t
P
Fsx
P
Fbr
P
M
F
M
F
M
F
16
13
16
13
17
13
17
13
17
13
17
13
15
13
17
,655
,677
,390
,378
,298
,294
,095
,102
.149
,158
,349
,322
,035
,041
59.24
84.30
,044
,049
,011
.011
,091
,086
.239
,219
1.636
1.530
,107
.115
.115
-083
.057
.053
.025
.018
-032
-028
.051
.048
.009
.012
6.17
5.36
.006
-007
.002
.002
-013
.012
.026
.022
.223
.I26
-544
,591
2.415
,133
5.275
,031
,196
,846
.050
,827
,903
,361
,218
,828
,427
,526
6.576
,017
.458
,839
.180
5.962
327
,844
,406
,008
,930
7.287
,012
1.506
,143
,798
,390
3.669
.067
,213
4.621
,042
1.714
,703
4.146
,053
,764
,253
M
F
Post 115
M
F
Sp1enia 1
M
width
Antcomm
F
Brain
weight
Ratiol
Ratio2
M
F
M
F
M
F
M
F
Ratio3
M
F
Ratio4
M
Ratio5
F
M
F
11
16
11
17
11
17
11
16
11
16
11
-.752
-1.276
1.102
-1.614
,280
,119
,062
.95
1.053
,302
2.263
.032
1.417
,169
'Results from t-tests andANOVA(ana1ysis 0fvariance)for the regions studied.The t-value is based on apooled variances. Fsx and Fhr are
F-ratio values from ANOVA for sex and brain weight respectively. Values significant at less than p = .05 are italicized.
"Area is in mm2.
353
SEXUAL DIMORPHISM IN PRIMATE CORPUS CALLOSUM
TABLE 2. Macaca mulattal
Region
TotalCC
AntCC
PostCC
Next 1/5
Post 1/5
Splenial
width
Antcomm
Brain
weight
Ratio1
Ratio2
Ratio3
Ratio4
Ratio5
Sex
N
Area2
s.d.
M
F
M
F
M
F
M
F
M
F
M
F
M
F
M
F
M
F
M
F
M
F
M
F
M
F
10
13
10
13
10
13
10
13
10
13
10
13
10
13
10
13
10
13
10
13
10
13
10
13
10
13
,959
,942
,523
.530
.444
.413
.142
.133
,240
.220
,417
.367
,075
,047
91.15
84.30
,049
,050
,012
,012
.094
,085
.253
.235
1.304
1.260
,136
,154
,097
,090
.05 1
.084
.024
,030
,022
,038
,038
,060
,115
,014
7.29
5.36
.006
,007
,001
,002
.009
,013
,028
,020
,206
.117
P
Fsx
P
Fbr
P
,278
.78
,639
,442
5.081
.036
p.190
.85
1.602
,220
4.114
,056
1.009
.32
.048
.831
3.509
.076
.734
.47
,021
.887
3.992
,059
1.457
.16
,771
.400
2.187
255
2.261
.03
2.93
,102
2.384
,138
,876
.39
.001
,975
3.158
,090
,010
1.386
,253
t
2.65
.01
-.461
.65
,766
.45
1.92
.07
1.82
.08
.66
.52
8.12
'Results from t-tests and ANOVA (analysisof variance) for the regions studied. The t-valueis based on a pooled variances. Fsx and Fbr are
F-ratio values from ANOVA for sex and brain weight respectively. Values significant at less than p = .05 are italicized.
2Area is in mm2.
significant sex differences in any of the species,
Brain weight was significantly higher in
male M . mulatta than i n females of this
species. Using ratio data, i.e., correcting for
brain weight, these data did not provide
evidence for significant sex differences, except in the case of Ratio4, the relative
amount of splenial portion comprising totalCC area. Here, ANOVA shows the only
sex effect that is significant in M . mulatta,
The p value for M . fascicularis is .053, also
suggesting some dimorphism. In both cases,
however, the male values are higher, a finding the opposite of that from the human data
(see Discussion). Neither of the New World
monkey species examined here showed any
significant dimorphism in primary measures (including brain weight) or in the ratios.
DISCUSSION
Very little evidence for sexual dimorphism
in the morphology of the CC in four monkey
species was found in the samples presented
here. These results are consistent with those
of de Lacoste and Woodward (1988),who did
not find dimorphism in the cross-sectional
areas of the CC in New and Old World monkey brain samples. The TOTALCC area ofM.
fascicularis was higher in females, but not
significantly so. In contrast, the M . mulatta
male sample had a larger TOTALCC area.
SPLENIAL WIDTH was higher in males
than in females in both macaque species, a
finding not reported above and opposite to
those reported by de Lacoste-Utamsing and
Holloway (1982) and Holloway et al. (1986)
for Homo. In the former case, i.e., TOTALCC
area, the ANOVA analysis shows that the
dimorphism is best explained by dimorphism in brain weight. However, Ratio4
(POSTERIOR % divided by TOTALCC) is a
true sex effect, without strong allometric
dependence, which in these samples, favors
the male of the macaque species. We frankly
do not understand why this reversal occurs.
There does not appear to be any behavioral
data to suggest that visuospatial task performance shows significantly higher scores in
male macaques than in females. While be-
354
R.L. HOLLOWAY AND P. HEILBRONER
TABLE 3. Callithrix jacchus
Region
TotalCC
AntCC
PostCC
Next 1/5
Post 1/5
Splenial
width
Antcomm
Brain
weight
Ratio1
Ratio2
Ratio3
Ratio4
Ratio5
Sex
M
F
M
F
M
F
M
F
M
F
M
F
M
F
M
F
M
F
M
F
M
F
M
F
M
F
N
10
7
10
7
10
7
10
7
10
7
6
5
10
7
10
7
10
7
10
7
6
5
10
7
10
7
Area
,167
,161
,081
,079
,087
,082
,030
,028
,046
,045
,043
,011
,165
,184
7.85
7.61
,043
,042
,012
.012
,022
,006
,280
,280
7.19
7.34
t
,030
,018
,020
.012
.012
.010
,007
,003
.006
,006
,072
,497
.63
,157
,702
,208
,660
.136
.89
.018
396
,000
,999
.927
.37
.491
,502
1.350
,265
.606
.55
,141
,717
1.358
,263
,447
.66
.061
A11
.961
,354
,989
.34
4.654
,063
,642
,454
.43
1.734
,209
3.556
.080
,026
377
,472
,510
P
Fsx
Fbr
s.d.
P
P
,002
.059
,025
,511
,689
,007
,005
,001
.002
,038
,001
,037
,037
1.003
377
-309
,820
.42
,173
.86
,103
.92
.972
.36
p.015
.99
p.315
.75
'Results from t-testsand ANOVA (analysis of variance) for the regions studied. The t-value is based on a pooled variances. Fsx and Fbr are
F-ratio values from ANOVA for sex and brain weight respectively. Values significant a t less than p = .05 are italicized.
havioral reasons cannot be ruled out (as
many have yet to be thoroughly studied), we
prefer to regard this unique finding as a n
example of statistical artifact, until larger
samples are described.
While sexual dimorphism appears in humans, and de Lacoste and Woodward (1988)
suggest that it is present in pongids and
prosimians, we strongly urge that larger
samples will be necessary to demonstrate
whether or not larger female CC's are a
shared character state in haplorrhine primates.
The correlational Tables 5-8 indicate
many interesting possible relationships. We
note, in particular, the higher correlations
between variables in the larger sample for
M. fusciculuris than in M . mulattu. Yet neither the splenial wideth nor the splenial area
correlates significantly with brain weight,
while showing strong and significant correlations with TOTALCC area. The anterior
commissure only has significant correlations
with TOTALCC area and the anterior half of
the CC, ANTCC. In effect, each species
shows a unique set of correlation coefficients, with negative correlations between
splenial width, brain size, and TOTALCC
area being more common in Callithrix and
Sa.guinus. We frankly do not know whether
these unique patterns are truly species-specific indicators of possible neural reorganizational differences in the corpus callosum, or
simply statistical artifacts due to sampling.
Only larger sample sizes including more species will clear up this question.
The anterior commissure interconnects
contralateral temporal polar cortices (McCullough and Garol, 1941; Ebner and Myers,
1965; Cippolini and Pandya, 1985). This cortical area is generally thought to have a close
affiliation with the limbic system. No sex
differences of any statistical significance appear in these data. We draw attention to the
very small area of this structure, however,
and the greater consequent possibility of
355
SEXUAL DIMORPHISM IN PRIMATE CORPUS CALLOSUM
TABLE 4. Saguinus oedipus1
Region
TotalCC
AntCC
PostCC
Next 1/5
Post 1/5
Splenial
width
Antcomm
Brain
weight
Ratio1
Ratio2
Ratio3
Ratio4
Ratio5
Sex
N
Area
s.d.
t
P
Fbr
P
M
F
M
F
M
F
M
F
M
F
M
F
M
F
M
F
M
F
M
F
M
F
M
F
M
F
11
10
11
,164
,164
.084
.086
.081
.079
.043
,043
,043
,046
,177
,181
,012
,014
9.48
9.93
,037
.036
,010
.010
,012
,017
.011
.012
,006
,008
,006
.039
.97
,000
.845
,012
,915
p.411
.69
.238
637
.040
.845
,626
.54
,470
.508
,018
,896
-1.007
.33
1.833
-192
,729
,413
-1.365
.19
1.474
.241
,318
,586
-.465
.65
,183
-678
,021
.887
-284
.39
.435
.527
,997
.345
-1.427
,170
1.887
,186
.789
,395
10
11
10
11
10
11
10
11
10
11
10
11
10
11
10
11
10
Fsx
.055
,006
.005
,020
,020
.003
,004
,687
,753
,003
,004
,001
,001
,010
,010
,029
.028
,647
,758
,084
11
10
11
10
11
10
P
,085
,263
.284
5.976
6.256
,737
,470
-.I47
,464
-.154
379
-1.617
.122
-.945
.356
'Results from t-tests and ANOVA (analysis of variance)for the regions studied.The t-valueis based on a pooled variances. Fsxand Fbr are
F-ratio values from ANOVA for sex and brain weight respectively. Values significant a t less than p = .05 are italicized.
In sum, there does not appear to be any
correlation between known behavioral and
overall anatomical dimorphism with a dimorphic counterpart in the corpora callosa of
New or Old World Monkeys.
measurement error than with the other
structures measured. Anterior commissure
measurements on human brains by Demeter
et al., (1988),do not indicate any significant
human dimorphism.
TABLE 5. Correlation (Pearson) matrix for Macaca fascicularis'
brain
brain
totalcc
antcc
-
totalcc
.40
(.03)
-
antcc
.16
~41)
.45
(.01)
-
postcc
post5
next
antcomm
splenial
.45
(.01)
.90
t.00)
.44
.47
(.01)
.82
.43
(.02)
.80
.24
(.23)
.65
.35
(.OO)
(.OO)
.48
(.01)
.92
(.00)
.34
(.02)
postcc
post5
next
antcomm
-
-
.91
.I7
(.00)
-
.20
(.W
61
(.00)
.57
(.00)
.58
(.00)
splenial
IPearson Correlations for raw measurements on the corpus callosum for each species with two-sided p values.
-
.59
(.OO)
.46
(.01)
.76
(.W
.90
(.00)
.56
(.0Q
.35
~07)
-
356
R.L. HOLLOWAY AND P. HEILBRONER
TABLE 6. Correlation (Pearson) matrix for Macaca mulatta'
brain
brain
-
totalcc
antcc
postcc
post5
next
antcomm
.44
.40
(.W
.90
.39
(.07)
.84
.31
(.15)
.I7
.41
(.05)
.79
.36
(.08)
.43
(.OO)
(.OW
(.OO)
(.OO)
.54
.47
(.02)
.94
.53
(.W
.92
(.OO)
(.OW
(.W
-
totalcc
-
antcc
(.W
postcc
-
-
post5
.81
(.OW
next
-
.47
(.02)
.26
03)
.26
(.22)
.22
~32)
-
antcomm
splenial
splenial
.31
~ 5 )
.45
(.03)
.22
~31)
.65
(.OW
.72
(.OO)
.47
(.02)
.10
(.66)
-
'Pearson Correlations for raw measurements on the corpus callosum for each species with two-sided p values.
TABLE 7. Correlation (Pearson) matrix for Callithrix jacchusl
brain
totalcc
antcc
uostcc
Llost5
next
antcomm
sulenial
.43
brain
totalcc
antcc
postcc
(.W
.02
post5
next
antcomm
splenial
'Pearson Correlations for raw measurements on the corpus callosum for each species with two-sided p values.
TABLE 8. Correlation (Pearson) matrix for Saguinus oedipus'
brain
totalcc
brain
totalcc
antcc
postcc
post5
next
-
-.02
(.91)
-.05
(.84)
.03
(.W
.13
(.58)
.51
(.0%
.23
(31)
.59
p.19
~41)
-.05
-
.84
(.OO)
antcc
postcc
-
.58
(.OO)
.05
(.8U
-
(.OO)
post5
next
antcomm
-
(.82)
.09
(.W
-.25
(.28)
-.06
(.79)
-
antcomm
.25
~32)
-.21
(.43)
-.17
C51)
-.15
(.57)
-.02
(.92)
.44
(.08)
splenial
'Pearson Correlations for raw measurements on the corpus callosum for each species with two-sided p values.
-
splenial
.03
(38)
.56
(.OU
.26
(.23
.63
(.OO)
.79
(.OO)
,023
(.73)
-.03
(.88)
-
SEXUAL DIMORPHISM IN PRIMATE CORPUS CALLOSUM
ACKNOWLEDGMENTS
The authors are grateful for partial support from NSF-BNS-84-18921 (R.L.H.) and
to the Primate Research centers described in
the Methods section. The comments of unknown reviewers were also very helpful to
us.
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