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Thickness of the male white cranium.

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THICKNESS O F THE MALE WHITE CRANIIJM
T. WINGATE TODD
Hamann Museum of Comparative Anthropology and Anatomy,
Western Reserve Universzty, Cleveland, Ohio
THREE FIGURES
AVERAGE CRANIAL THlCKNESS AND I T S RELATION TO AGE
A study of the thickness of the cranium needs no introduction. Our information upon the subject is scanty in the
extreme. Krause indeed makes the following statement :
“Die Wandungsdicke betragt ca 15 mm. an der Protuberantia
occipitalis externa ; am Schiideldach schwankt sie zwischen
5-7 mm. und sinkt auf 2 mm. an der Squama om. temporium.,’(2). More precise data are not available. It has long
been held that in old age the cranium becomes thinner,
although Henle (I) reminded his readers that Lucae (3) had
questioned whether the diminishing weight of the skull in
senility might not be associated with atrophy in the facial
skeleton rather than with changes in the cranial bones.
I n order to obtain more exact information on the thickness
of the cranium and its relation t o age, I have taken measurements upon 448 male white crania of known age o r of age
determined to within a year or two by methods which I have
previously outlined, and I have subjected this material to a
detailed examination the results of which I propose now to
record. Each skull was set up on the Reserve Craniostat (5’6)
in the Frankfort plane; the maximum glabellar length and
auricular height were determined. ?Vith Plower’s craniometer the maximum breadth was obtained and the Eurya
marked. The points involved in these measurements were
penciled upon the cranium. The skull being already bisected,
245
THE ANATOMICAL RECORD, T O L . 27, NO. 5
246
T. WINGATE TODD
it was easily unpinned and the two halves taken apart. The
thickness of bone at each of the sites mentioned was then
determined with a large Martin’s Tasterzirkel and recorded.
In those skulls which had been opened at autopsy and therefore had had the calvarium removed instead of being bisected
in the sagittal plane, the frontal thickness was obtained by
Martin’s Koordinatenzirkel. All measurements were determined to the nearest quarter millimeter. The thickness at
t
Fig. 1 Age distribution of 445 male skulls used in the calculation of average
cranial thickness. Note the peaks a t each decade and half decade. The threeyearly running average eliminates these irregularities. Ordinates refer t o years ;
abscissae t o number of skulls. (By accident three of the 448 skulls are omitted
in the figure.)
the Euryon on right and left sides was averaged. Thus we
obtained a series of determinations of thickness at the following sites : frontal area (glabella) including the frontal
sinus, Opisthion, vertical point, Euryon. It is obvious that
the thickness at the Opisthion is more serviceable than
Krause’s measurement at the external occipital protuberance.
My secretary, Miss Lindala, arranged the series in order
of age and the three-yearly running average was ascertained.
It is to be understood that all measurements were determined
twice, that all figures have been checked and all calculations
247
THICKNESS O F MALE WHITE CRANIUM
7
-:
OCClnTALiL
-
-
-
---
I
I
-
7-
VERTEX 6-
4-
EURYON
I
1
1
1
I
4-
I
1
&
Fig. 2 Unsmoothed graphs of the running averages a t four cranial sites plotted
on arithmetic grid. This figure is included in order to contrast its effectiveness
with that of figure 3. Ordinates in years; abscissae in millimeters of thickness.
Figure 2 presents the unsmoothed graphs of the running
averages on arithmetic grid paper at each of the four sites
chosen from nineteen to eight-two years. Thickness is recorded in millimeters. From twenty-nine to fifty-two years
the graphs, except that of frontal thickness, possess a very
smooth appearance. During this period the occipital thick ness is practically constant at approximately 6 mm.; thickness at the vertex increases slowly from 5.4 mm. to 6.0 mm. ;
at the Euryon thickness increases from 2.9 mm. to 3.5 mm.
Other studies which we have made convince us that the
period from just under thirty years to just over fifty years
248
T. WINGATE TODD
is the most stationary period in differentiation of the skeleton. We were not surprised, therefore, to find that cranial
thickness during this period alters very slowly or not at all.
We were also prepared to find a greater swinging of the
graphs before and after this period of lull in cranial differentiation. It is noteworthy that oscillation of the graphs is
more marked after fifty years than under thirty years. A
glance at figure 1indicates that the cause for this appearance
is not found in the comparative paucity of material; it is
rather to be sought in a sporadic thickening of the cranium
during later life. We find, then, no evidence of real diminution in thickness of the cranium with increasing age and
share Lucae’s view of the causation of senile loss of skull
weight.
From a study of the age relationship in frontal thickness
we note the extreme individual variability in dimensions of
the frontal sinus and t,hat this sinus does not appreciably
increase in dimensions during adult life. The average frontal
thickness of the cranium is not far from 11.0 mm. The occipital thickness and vertex thickness are each nearly 6.0 mm.
and the thickness at the Euryon approaches 4.0 mm. Disregarding age, these averages are found mathematically to
be the following :
Average thzckness
Glabella,
Opisthion,
Vertex,
Euryon,
11.26
5.73
5.88
3.56
mm.
mm.
mm.
mm.
There is a serious objection to plotting running averages
on arithmetic grid: it gives no adequate idea of the percentage variations. I have therefore plotted the distribution
upon arithlog grid and present the results as figure 3.
We shall see later that by adding the coefficients of rariation for each of the four types of male white cranium shortly
to be differentiated, and dividing the sum by four we obtain
the following average coefficients of variation for each of the
several sites of measurement in thickness :
249
THICKNESS O F MALE WHITE CRANIUM
Glabella, 23.19 ; Opisthion, 29.53 ; Vertex, 21.78 ; Euryon,
29.28.
Figure 3 gives at a glance a rough idea of the same result.
It is obvious at once that the Opisthion and Euryon are the
most variable areas of cranial thickness, and this is naturally
clue to the erratic development of external body ridges at the
1
T
1
1
T.
T
T
1
1
1
T
1
1
FRoyru
OCClPlTU
VERTEX
EURYON
AGE
11
20
1
1
1
1
1
1
1
1
1
1
1
1
25
30
35
40
45
50
55
60
65
70
75
80
12.0
Fig. 3 Unsmoothed graphs of the running averages in cranial thickness plotted
on arith-log grid t o demonstrate visually the relative percentage variability at
each site. Compare these graphs with the figures in table 1. Ordinates refer to
years ; abscissae to millimeters of thickness.
former and to the marked local irregularity of endocranial
bony surface at the latter site. Glabellar thickness, much to
my surprise, shows no such large variability. Also there is
no progressive increase in thickness shown on the graph. I
therefore conclude that after early adult life there is no
usual further encroachment by the frontal sinus. The very
variable supra-orbital ridges of course do not figure in this
measurement. Like the glabellar region, the area of the
250
T. WIPI’GATE TODD
vertex is relatively less variable. But unlike the Glabella,
the vertex shows a definite trend of increasing thickness on
the graph. Allowing for irregularities, cranial thickness at
the vertex does increase with age from early adult life up till
about sixty years. Thereafter there is no definite decrease
in thickness, the oscillation of the graph being accounted for
by paucity of material. This increase in thickness related t o
age may be observed in the curve of the Euryon and t o a
slighter extent also in that of the Opisthion. It does not
occur at the Glabella. There is, then, a small but definite
inclination on the part of cranial thickness t o increase with
age up to about sixty pears.
No one of the curves exhibits a real tendency toward decrease in thickness after sixty. Consequently we must hold
with Lucae that diminishing weight of the skull in senility,
a phenomenon which undoubtedly occurs and is amply confirmed in studies to be published by my colleague, Doctor Ingalls, results from atrophy in the facial skeleton rather than
from chaiiges in the cranial bones.
The oscillation of these unsmoothed graphs demonstrates
visually the utter impossibility of predicting the probable
thickness of the cranium at any age and the error into which
one may fall if one attempt to use mere cranial thickness as
an age indicator.
RELATION O F CRANIAL THICKNESS TO CRANIAL T Y P E
It has been usual t o invoke the cephalic index as a rough
method of distinguishing between cranial types. I n the course
of our studies we have come to regard cephalic index as
merely one of the compensatory methods by which cranial
form is adapted to cerebral volume. The determining factors
for cephalic index are to be sought primarily in the initial
conformation of the cranial base. I believe that I have obtained a more precise method of subdividing crania into types
-a method which will be fully presented upon another occasion. The fundamental principle of this subdivision is the
relation between cerebral (or perhaps it were safer, at pres-
THICKNESS O F MALE WHITE CRANIUM
251
ent, to say possible physiological brain) volume and cranial
dimensions. By modifications of contour some crania accommodate a greater brain volume than others of the same
linear dimensions. By this method I have segregated four
cranial types which for essentially the same linear dimensions
possess the following average possible physiological brain
volumes. (For a discussion of the possible physiological
lorain volume see 7.)
a. 1307 cc.
p. 1383 cc.
y. 1449 cc.
6. 1501 cc.
Industrial fluctuations and social upheavals following the
war have provided an illuminating means of demonstrating
the reactions of each of these types of individual to existing
conditions of civilization. Closer investigation of the types
demands an inquiry into the thickness of cranium characteristic of each.
From 1917 to 1922, inclusive, our material includes the following numbers of male white skulls definitely allocated to
each type : a, 38 ; P, 39 ; y, 43 ;6,49. From so slender a material
it would be unwise to draw too far-reaching conclusions.
Nevertheless, the sample provides a reasonable working test
of the justification of our segregation. Niss Lindala has
therefore calculated f o r me the means and variabilities in
thickness f o r each type in this sample, and her results after
being checked by myself are presented in the table below
(table 1).
There is apparently a diminishing scale of thickness in each
dimension in the ascending series of crania from type a to
type 6. The significance of this diminution must be considered, but first of all a glance at the variabilities is important.
The coefficients of variability range between 18 and 34 per
cent. This is a very high degree of variability and type of
cranium has no real influence upon the variability. Without
some comparison, however, it is impossible t o realize the
unusual degree of this variability. From time to time there
252
T. WINGATE TODD
have been gathered tables of variability in different bodily
dimensions, but in these tables there is evident no significant
order of variability. From a study of our own material I
am led t o infer that the apparent chaos of such tables result,s
from the very heterogeneous material utilized, the different
methods employed by the several observers from whose investigations the figures are obtained, and the inadequacy and
uncertain character of the material itself. Upon another occaTACLE 1
YEAN
STANDARD D E V I A T I O N
COEFFICIENT O F
VARIATION
a. Glabella..
. . . . . . . . . . . 11.8 -C .323
Opisthion . . . . . . . . . . . 6.1 f 2 2 9
Vertex . . . . . . . . . . . . . 6.2 2 .145
Euryon . . . . . . . . . . . . . 3.7 -1- .122
2.95 ? 2 2 8
2.10 f .162
1.33 k .lo3
1.12 & .087
23.00 -+- 2.052
34.43 C 2.962
21.45 2 1.726
30.27 C 2.553
p. Glabella ............ 11.5 -C .225
2.08 2 .159
1.45 2 .111
1.17 2 .089
1.23 2 .094
18.09
24.17
20.17
33.24
t 1.424
Opisthion . . . . . . . . . . . 6.0 i.l57
Vertex ............. 5.8 f .126
Euryon . . . . . . . . . . . . . 3.7 f 2 3 3
. . . . . . . . . . . . 11.0 -C .257
Opisthion . . . . . . . . . . . 5.7 f .178
Vertex . . . . . . . . . . . . . 5.9 -C .l50
Euryon . . . . . . . . . . . . . 3.5 2 .097
2.50 2 .182
1.73 2 .126
1.46 & .lo6
0.94 2 .068
22.73
30.35
24.75
26.86
C 1.736
C 2.406
............ 9.8 -C .254
Opisthion . . . . . . . . . . . 4.9 -C .138
Vertex . . . . . . . . . . . . . 5.2 f .lo4
Euryon . . . . . . . . . . . . . 3.1 4 .080
2.64 iA80
1.43 i- .097
1.08 2 .074
0.83 4 .057
26.94
29.18
20.77
36.77
2 1.964
y. Glabella
6. Glabella
-t 1.938
2 1.602
& 2.805
2 1.908
t 2.090
C 2.147
3- 1.472
4 1.952
sion it will be necessary to discuss fully the very definite
order of variability shown by a material of known origin and
ascertainable selection like that housed in this institution, and
to formulate what may conveniently be defined as the laws
of variability in anthropometry.
I n order to emphasize this order of variability in a preliminary manner, I have drawn a p table 2 from the records
of our investigations on the Reserve material. The standard
of variability is that of standing height. This indicates
roughly the variability of the body as an entity. Sitting
height closely resembles it. Whereas the variability of the
THICKNESS O F MALE WHITE C R A N I U X
253
body as a whole is not far from 3.5 per cent, the variability
of major parts, leg and skull, f o r example, is between 4 and 5
per cent. Variability of segments of these major parts,
namely, femur length and internal nasal length, is between
5 and 6 per cent. Upon such a basis of comparison we may
infer that some real restraining influence is at work upon
dimensions like epicondylar breadth of the femur and cranial
breadth. Cranial capacity, as we are taught from a study
TABLE 2
W e s t e r n Reserve material-Hamann Museum
Coeficients of variation: W h i t e males
NUIBER
100
100
100
100
100
167
167
167
50
30
167
45
49
43
43
14
DIMEKSlOb
Standing height
Sitting height
Leg length (cristal h t )
Femur length R. (maximum)
Femur epicondylar breadth R.
Cranial length (R.R.)
Cranial breadth
Cranial auricular height
Internal cranial length
Internal nasal length
Cranial capacity
Dura volume
Thickness cranium (vertex 8.)
Thickness scalp length
Thickness scalp breadth
Thickness scalp auricular height
COEFFICIENTS O F
VARIATION
3.55 t- 0.146
3.77 t- 0.180
4.69 2 0.219
5.65 t 0.270
4.61 & 0.220
4.51 t- 0.166
3.93 & 0.117
4.14 2 0.152
3.79 2 0.25
5.30 2 0.36
8.45 t- 0.297
12.62 2 0.911
30.77 t 1.472
62.13 t 6.014
40.00 & 3.343
22.41 & 3.144
of cranial types, displays an expected fairly large degree of
variability and, considering its small bulk, dura volume must
be under some restraining influence. Scalp variabilities are
unusually great, and these are discussed at length elsewhere(8). For reasons therein disclosed, 20 per cent is regarded as the typical scalp variability, and it is apparent
from a consideration of table 1that scalp thickness and skull
thickness are both of the same order of variability.
At present, then, one would point out that our experience
indicates the degree of variability shown by cranial thickness
to be much greater than we should expect were there any
254
T. WIKGATE TODD
true natural selection in cranial thickness. I consider that
Nature is not greatly concerned over the mere thickness of
the cranium, and we can never expect to predict this measurement with any real accuracy. It is plain, however, that the
6 type cranium stands somewhat apart from the others in its
definitely thinner bone: it is less clumsily made and shows
a higher grade of what the French have termed ‘perfectibilitk. ’
In order to demonstrate the difference in thickness between
the types of skull, I have calculated the odds against the
difference in the mean thicknesses of series a and series 6
being due merely to random sampling. The result of this
investigation is given below.
Odds against difference i n thzckness betweem a and 6 bezng t k e result of
random sampling
Glabella thickness,
962 t o
Opisthion thickness,
408 to
Vertex thickness,
13,279 t o
Euryon thickness,
109 to
1
1
1
1
I n order to realize the significance of these figures we must
bear in mind that statistically odds of 199 to 1 are regarded
as good evidence of a real difference-a difference too great
to be accounted f o r merely by the natural inadequacy of the
sample to represent truly the entire population( 4). Another
method of evaluation represents the difference between the
means in terms of the standard deviation of this difference.
If the difference is three times its standard deviation, the
probability is great that there is a fundamental distinction
between the two samples ; if the difference is three-and-a-half
times its standard deviation, the probability amounts to a
certainty. Now the differences between the means of the
several dimensions in series a and series 6, each in terms of
its standard deviation, are the following :
At
At
At
At
Glabella,
Opisthion,
Vertex,
Euryon,
3.28
3.03
3.79
2.78
THICKXESS O F MALE WHITE C R A N I U M
355
Hence by either method one legitimately concludes that
between series a and series 6 there is a significant difference
in thickness of the cranium except in the region of the Euryon.
The difference is too small to be put to practical use in computing cranial capacity (or rather total possible physiological
brain volume) in the living, but nevertheless it exists. It is
also worthy of comment that the difference is most certain in
the vertex, the site above all others where bone thickness is
uncomplicated by confusing features present at each of the
other locations, namely, in the glabellar area the frontal sinus,
at the Opisthion external ridge development, and at the
Euryon relatively large variations consequent upon modeling
of the inner table upon temporal convolutions.
I have already advanced the hypothesis that Nature is not
greatly concerned over the precise thickness of the cranium,
and yet I have demonstrated that there is a significant difference in thickness between type a and type 6 skulls. This
apparent contradiction requires explanation. From other
studies now in progress I contend that the a type cranium is
in general a clumsily built, ill-filled brain case and fundamentally different from the cranium of the 6 type, although
there are some crania originally probably of the 6 type which
secondarily, as a result of pathological thickening, simulate
specimens of the a type. Further discussion of this thesis
is irrelevant here. The point which I desire to make is that
thickness is a mere incident in the configuration of the cranium. The 6 type is a finer grade of cranium, more delicately
and finely fashioned and better filled with brain. Hence
actual cranial thickness is less in the 6 type than in the a type.
But apart form this general modeling there is no evidence of
an effort to control cranial thickness itself. We may observe
this lack of control in the fact that there is no significant difference between a and 6 types in variability of thickness.
256
T. WINGdTE TODD
SUMMARY
1. Average thickness in male white crania is given by the
following figures : Glabellar area, 11.3 mm.; Opisthion, 5.7
mm. ; Vertex, 5.9 mm. ; Euryon, 3.6 mm.
2. Cranial thickness increases slightly with age up to about
sixty years, but thereafter there is no real evidence of any
normal change.
3. Cranial thickness is so variable that it appears unreasonable to imagine it under specific natural control as many
dimensions seem t o be. It is so variable that one may not
expect to predict it with a real degree of accuracy for any
particular cranium.
4. Segregation of crania upon a basis of the relation of
capacity to linear dimensions indicates at least four types
of male white skulls, of which the most finely modeled and
best-filled type has cranial walls significantly thinner except
at the Euryon than those of the lowest type.
5. Cranial thickness is of the same order of variability as
scalp thickness.
LITERATURE CITED
1 HENLE, J. 1871 Handbueh der systematischen dnatomie des Menschen.
Braunschweig, 3. Aufl., Bd. 1, Abt. 1, Knoehenlehre, S. 220.
2 KRAUSE,C. F. T. 1879 Handbuch der nienschlichen Anatomie. Hannover,
3. Aufl., Bd. 2, S. 55.
3 LUCAE 1861 Zur Morphologie der Rassenschadel. Frankfurt, Bd. 1, S. 7.
(Ref. from Henle.)
R. 1923 Medical biometry and statistics. Phila., p. 258.
4 PEARL,
5 TODD, T. W. 1923 Cranial capacity and linear dimensions in white and
negro. Am. Journ. Phys. Anthropol., vol. 6, p. 148.
6
1923 Effeet of maceration and drying upon the linear dimensions of
the green skull. Journ. Anat., vol. 57, p. 338.
7
1923 Dura volume in the male white skull. Anat. Rec., vol. 26,
pp. 263-273.
8 TODD,T. W., AND KUENZEL,W. 1924 The thirkness of the scalp. Journ.
Anat. (in press).
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