CONTRIBUTION TO T H E ANTHROPOLOGY O F THE BRAIN C. J. CONNOLLY Catholic University, Washington, D. C . ONE FIGURE At the present time, the most intensive work on the brain is directed toward its microscopic anatomy. Previous decades have witnessed very detailed studies of the external features of the brain, especially the convolutions, and comparisons have been made regarding the comparative development of the brain in different races. It would almost seem that this phase of brain study had become a closed subject. But it has recently been pointed out by some investigators both in America and Europe that the results so far attained a r e far from being satisfactory and are, in fact, often contradictory. Though detailed studies of sulci and convolutions have been made on specimens representing different races, the number studied is often small, so that the degree of variation in dimensions of the brain and its parts cannot be estimated. hloreover, indices by which the general shape of the brain in different races could be compared a r e frequently lacking. Again, there is no generally accepted standard method of measuring the brain such as exists for the skull, and it is thus difficult to compare the results obtained by different authors. I t is important to know the average dimensions and degree of variability in the brain of a sufficiently large series of each race. Much work is yet to be done on this problem, though a difficulty exists in obtaining ample material in the case of certain races. 477 ANERICAN J O U R N A L OP PHYSICAL A N T R R O P O W G Y , VOL. XV, NO. 3 APRIL-JUNE, 1931 478 C. J. C O N N O L L Y The material used in this investigation was that preserved in the U. S. National Museum, Division of Physical Anthropology. The collection constitutes a series of well-hardened brains. A few that were slightly damaged or deformed are not included in this study. Measurements were, however, made on small groups or on single specimens representing different races, but these are omitted here as not being significant for a comparative study. This study gives the results of measurements made on the 240 hemispheres of 120 brains of adults representing white, negro, and Malay races. The brains of the whites (German) with Berlin as their source were all hardened by injection in situ, while the negro brains were hardened after removal from the skull by HrdliEka and weighed by him. The number of male specimens of these two races is about equal and sufficiently large to indicate the degree of variation and also to permit of some comparison regarding general form. The miscellaneous whites are of various European nationalities, and it was thought advisable to treat these separately from the uniform series of German whites. The Malay (Filipino) group is much smaller and may not represent the true average of the race. Particular attention was given to method, for the structure of the brain naturally presents difficulties in obtaining exact measurements, and it is desirable that more uniformity be reached as to what should be measured and in what manner. Hence many measurements were taken in the effort to ascertain which were the more significant and most reliable. I n his study of “An Eskimo brain” and in his “Anthropometry,” HrdliEka ( ’01, ’20) proposed a simple method of taking any desirable horizontal distance and expressing this as a percentage of the total horizontal length of the hemisphere. The method “consists of taking the maximum antero-posterior diameter of each hemisphere as a basis and a horizontal to which all other measurements are referred as so many verticals.’’ ANTHROPOLOGY OF T H E B R A I N 479 More recently, Ariens Kappers ( ’27) independently suggested a somewhat similar method in his valuable paper, but here the horizontal used a s a base upon which the various verticals a r e erected is “the line connecting the base of the operculum orbitale with the base of the occipital lobe-the lateral horizontal” and extending between the frontal and occipital perpendiculars. Apart from the chief indices, such as length-breadth index, which Rappers measured directly on the brain, the various other indices were measured on photographs of the lateral and medial sides. The indices express the relation of a vertical at any chosen point on the brain, either to its distance from the frontal or occipital perpendicular o r its relation to the total horizontal. The occipital index is, for example, according t o Kappers, the parietal perpendicular or that from the highest point of the parietal lobe divided by its distance to the occipital perpendicular. For this study an apparatus was constructed for the purpose of taking measurements with the horizontal between the frontal and occipital poles as the base. Figure 1 shows a n isometric drawing of the apparatus. It consists of a rigid rectangular frame of walnut (26 X 27 X 16 em.) dovetailed at angles to prevent warping. At the bottom there is a n adjustable platform with a steel axis, the ends of which a r e held a t corresponding levels of ratchets. The platform can thus be inclined at various angles. At one end (left of figure) a glass plate is fitted flush with the inner wall of the frame. Across the top of the frame a beveled scale extends. This scale is rigidly fixed to a rider and can thus be moved backward and forward. The zero point of the scale is at the plane of the glass plate. Scales may also be inset along the top edges of either end of the frame to ensure accuracy of position of the longitudinal scale. Along the latter a depth gauge slides and its vertical scale can thus be brought over any point on the surface of the brain. F o r measuring very small brains, the platform may be raised to higher levels by adjusting to corresponding teeth of the rachets in front and back. 480 C. J. CONNOLLY T o take measurements, the brain is placed upon the platform with its frontal poles just touching the glass plate and its longitudinal axis parallel with the scale above. The platform is then so adjusted as to bring the frontal and occipital poles to the same horizontal level. This can be done accurately with the aid of a mechanic’s surface gauge (right of figure). The occipital poles may be more precisely located with the use of pins. It is generally possible t o bring the two frontal and one occipital pole to the same plane, just as skull i s placed on Frankfort plane by bringing the two lower orbital Figure 1 points and one porion into the same plane. When hemispheres a r e asymmetrical, each hemisphere is leveled separately. The projectional distances between any points on the surface of the brain may now be read off as distances along the base horizontal and expressed as percentages of this horizontal or projectional length of the brain. Likewise, any transverse diameter may be brought into this relation. Further, by means of the depth gauge, the height of any point above the base horizontal may be measured and likewise the distance of any point below the horizontal as in the case of the temporal perpendicular. The apparatus is thus essentially a space gauge by means of which the relations 481 ANTHROPOLOGY OF THE BRAIN of any point in the three dimensions may be given. Thus, from comparatively few measurements, the general contour of the brain may be reproduced. The maximum breadth was taken with spreading calipers and the maximum frontal breadth a t the level of the temporal poles, usually between the orbital opercula, with sliding compasses. The horizontal measurements of the brain were TABLE 1 - I m m MAXIMUM LENGTH, C Y . z RACE 2 ~ 3$ [ Xhx 37 M U White (German) 36 M U Miscellaneous whites 18 M White (German) I 1i 11 1 10 M u I Left -~ 5.23 I 12.4 12.5 0.41 0.68 0.75 15.7 15.8 12.9 10.5 0.54 0.58 0.44 0.39 6.69 0.51 5.48 12.1 12.5 0.41 0.58 0.50 15.6 15.9 12.8 0.92 0.97 j 0.82 6.18 0.33 5.37 12.2 12.7 0.32 0.65 0.74 10.4 0.68 16.0 16.0 13.4 10.6 0.83 0.97 1.14 0.71 Negro Right 16.2 16.3 12.5 10.1 6.22 0.62 0.83 1.10 0.55 0.54 ~ Negro TEYPOBAG OCCIPITAL DIAMETER, CM. 15.5 15.6 0.65 1.0 1 / 12.3 0.77 11.9 0.76 11.9 0.61 15.5 15.4 12.6 0.40 0.34 0.48 11.9 0.39 1 selected for the purpose of giving the comparative size of the main divisions of the brain. Table 1 gives the averages of the chief dimensions of the brain of four groups together with the standard deviations. It will be noted that, on the average, the left hemisphere is but 1 mm. longer than the right in negro and white (German) males. To check results of measurements with apparatus, the maximum lengths of all hemispheres were also 482 C. J. CONNOLLY taken with calipers. This likewise gave but 1-mm. difference, though the figures for whites were 1 mm. greater, while in the case of negroes, exactly the same averages were obtained. The method of measuring with the apparatus may therefore be considered reliable. A somewhat greater difference in favor of the left hemisphere is seen in the group of miscellaneous whites, where differences u p to 6 mm. in individual brains existed. In the smaller group of Malays the hemispheres are on the average equal in length, while in white females the right is on the average 1mm. longer than the left. These results are not in agreement with the widespread belief that there is a considerable difference in the size of the two hemispheres. A contrary opinion was expressed by Jaeger (’14) on the basis of a study of the volume of the cortex in the two hemispheres, though only a few brains were studied. Berger (’21) found no pronounced difference in favor of the left hemisphere in his histological study, but his tables give a slight predominance in number of cells per unit area in favor of the left. Nevertheless, the left hemisphere is larger in a greater percentage of cases. Our results harmonize well in this respect with those of HrdliEka ( ’07), who found slight but definite differences in favor of the left side in the sum of the lengths of the cranial fossae and in the maximum ventral anteroposterior diameter. He states that “there is therefore a clear, though small excess of fossal length on the left in the mass of human crania.” The following are the percentages in our groups of males in which the right or the left hemisphere is longer. Right Per cent Negro, White (German), Miscellaneous whites, Malay, 32.4 30.5 22.5 30.0 Left Per cent Equal Per cent 40.5 58.3 66.6 50.0 27.1 11.2 10.9 20.0 The predominance of the left hemisphere, however slight in amount, is clearly shown in these figures. The bilateral asym- ANTHROPOLOGY O F THE BRAIN 483 metry is, moreover, greater in whites than in Malays and in Malays greater than in negroes. The female whites, however, show on the average a 1-mm. difference in favor of the right. I n the whole series of 120 brains, male and female, the right is longer in 31.7 per cent, the left longer in 50.0 per cent, and the hemispheres are equal in 18.3 per cent. The functional superiority of the left hemisphere is stated by Jacobi ('27) to be present in 95 per cent of cases. This is generally believed to be associated with prevalence of righthandedness and its assumed interdependence with localization of speech centers on left hemisphere. We should expect on this theory to have a larger percentage with excess size of left hemisphere, and as mentioned above, Berger finds no pronounced histological difference in the two hemispheres. Bethe ('25) doubts that right-handedness is something primary in a majority of people, but comes through exogenous influences, and believes it is still a n unsettled question that right-handedness is associated with functional predominance of left hemisphere. Comparing the two large series of whites (German) and negroes, we note that the negro brain is on the average longer, narrower, and flatter than the whites, with also a lower frontal height. The smaller group of miscellaneous whites show about the same relations. The average maximum height is, however, slightly smaller than in negroes, but the frontal height is greater. There is much overlapping in all the dimensions, as the standard deviations ( a ) indicate. The Malay brains occupy a position in some respects intermediate between whites and negroes. The average length and breadth is greater than in whites, but both maximum height and frontal height are lower. I n the temporal-occipital diameter there is an excess of length on the left side in negroes and whites. I n the small group of females the dimensions are smaller, but show generally the same relations in the two races a s the males do. The temporal-occipital diameters are here equal. 484 C. J. CONNOLLY BRAIN WEIGHT So many factors enter into consideration in dealing with brain weight that it is difficult to draw general conclusions. It is becoming ever more apparent that in itself brain weight in different races is not correlated with cultural status. Nor is this true even when stature is taken into account. Many researches seem to show this. Recently, Bushmakin ( ’28) found that Buriats who “ h m e entered the zone of cultural development only with the new state organization” have an average brain weight considerably surpassing the brains of Europeans and greater than that of Russians whose stature is higher than that of the Buriats. I n considering brain weight, as also other dimensions of the brain, we a r e here approaching the subject as one would any other organ from the anthropological side, namely, to attempt to ascertain the racial features and the degree of variability. Within the limits of a race there nevertheless seems to be a degree of correlation between brain weight and mental development. The following are the weights for the different groups : Females Males Negro, Whites (German), Miscellaneous whites, Malay, Number Weight in g r a m 36 36 14 10 119s 129s 1264 1310 Iiegro, Whites (German), Number Weight in g r a m 9 10 1127 1226 The average weight of the German brains is less than that usually given for the average of their population. This would be probably explained by the fact that unclaimed hospital subjects would represent the poorer, less-nourished individuals. This may also be true of the negro, though perhaps to a less extent. The group of Malay brains, if typical and not selected, show greater average brain weight than the whites. I n all three races and in males and females, the brain weights correspond quite closely with size dimensions, and especially with the chief dimensions as expressed by the cerebral module. 485 ANTHROPOLOGY OF T H E BRAIN Table 2 gives the chief brain indices. The cerebral or length-breadth index gives ratios which are typical of what we might obtain in any representative series for cranial indices in negroes, Malays, and Germans. Regarding the other three indices given in the table in which height is one member of the ratio, we must note first that our height dimension is taken from the frontal-occipital pole base line, and not from TABLE 2 Indices NUMRER RACE CEREBRAL OR LENOTHRREADTH BREADTH Br.xlOO Length H Z 0 Breadth :FS:\ RRIOHT- BRAINS I LENQTH FrLHn;,OO CEREBRAL MODULE LcB+ H 3 Males U Miscellaneous whites 18 M U Malay (Filipino) White (German) I 1 77.4 4.70 49.5 j 32.0 11.69 0.34 81.6 3.64 52.2 3.01 1 34.8 3.30 11.78 0.34 81.5 5.46 4.25 83.0 5.10 45.3 5.54 1 51.6 2.77 1 1.92 10 V 81.0 3.38 I 11.58 2.84 32.5 4.40 11.80 0.83 1.96 11.22 0.52 36.3 3.34 11.48 0.28 the horizontal connecting the base of these lobes. Hence height here given is smaller than would be obtained from base taken by Kappers. The negro brain being narrower than the white, the relation of the height to breadth is about the same in both races. With regard to frontal-height index, it will be noted that the ratio is higher in whites than in negroes, and in each race higher in females than in males. 486 C. J. CONNOLLY Regarding sex differences of the brain, several investigators, especially Retzius, have noted a simpler and more regular type of convolution in brains of females. Though the number of brains for the two sexes in our series is quite unequal, our observations support this view. The female brain is conservative i n type, with fewer secondary convolutions. It approaches more closely the youthful brain than does the male. As Retzius, however, states, there is no arrangement of sulci or gyri which is characteristic of the sex, as some assert. Landau ('23) was unable to determine sex in animal or human brains. The writer believes, however, that the sex can be determined in a large percentage of cases, though not to the same degree of accuracy as in the case of the skull. Apart from the more delicate membranes, regularity of sulci and convolutions, the general form of the brain reveals differences. And these differences are such as we might expect from a knowledge of the skull. The general form is more rounded, less angular. The general dimensions are, of course, generally smaller than in the male. But it is the relative dimensions that are of significance. The frontal region is relatively higher, the top of the brain flatter. The temporal lobe is smaller in length and depth and is more inclined medially when viewed from the lateral side. These characteristics are brought out in percentage relations and indices, though it is, of course, not maintained that by indices alone sex differences of individual brains can be revealed. Thus the frontal height, though absolutely less than in the males, is relatively greater in females as shown by the frontal-height index. Again, the temporal-occipital diameter is not only smaller absolutely i n females than in males, but also relative to the total length of the brain (table 4). The differences are again greater in whites than in negroes. Corresponding to the terminology of craniometry, we may speak of the mean of length, breadth, and height as the cerebral module (L+t+H). The figures are smaller, of course, than would be the case if the height were taken from the base of 0 487 ANTHROPOLOGY OF THE BRAIN frontal and occipital poles instead of from the frontaloccipital pole horizontal. The module for the ten Malay brains is higher than in whites and negroes, and this corresponds to the brain weight and other dimensions. Considerable attention has been given to the problem of symmetry in the fissures and convolutions of the two hemispheres. Landau, who has given special attention to this TABLE 3 1 RACE HOBIZONTAL DISTANCE, I N CENTIMETERS, FBOY FRONTALPOLE BER OF (BBAINSI i l ._ Negro 37 White (German) 36 ] 18 I Left M 7.4 ' 7.5 U 0.48 0.51 M U Miscellaneous whites Right M U 7.4 0.52 ' 7.7 0.58 1 Right I Left I Right I Left 13.8 0.59 13.9 0.59 8.9 0.36 9.3 0.64 7.6 0.43 12.9 1.20 13.1 0.56 8.6 1.61 9.3 0.60 7.9 0.62 13.0 0.97 13.2 0.98 8.7 1.04 9.4 0.68 13.6 0.82 8.6 0.73 9.0 0.46 Malay M U Females .___I Negro White (German) II M u M lo u 7.4 0.32 7.1 0.53 1 7.6 0.34 13.3 0.69 13.5 0.77 8.8 0.59 9.0 0.68 7.2 0.51 13.0 13.0 0.46 I 0.37 8.6 0.67 9.2 0.56 problem, reaches the conclusion that there is a fundamental bilateral symmetry of the two hemispheres and that any asymmetry present comes about by secondary growth differences. The projectional system of measurement i n a fairly large series offers some data for consideration. Table 3 shows the horizontal distances from the frontal pole to the principal fissures. We have taken the distances to the lower and upper ends of the central sulcus, but as these 488 C. J. CONNOLLY are relatively the same a s to the midpoint of the sulcus, we need take only the latter as a measure of the frontal length. I n cases where there was a sharp bend about the middle of the central sulcus, we have taken the midpoint on the line continuing the general direction of the sulcus. The horizontal distance to the parieto-occipital fissure was taken to the point where the fissure cuts the superior border. When the fissure does not cut the border, the point is taken where the fissure if extended would cut the border. The posterior end of sylvian fissure is the point of forking of the main trunk,. or when it does not fork, at the point where it turns upward. Quite striking are the small differences in the distances to the fissures on right and the left side. The excess, however slight, is constantly on the left side, with one exception. This excess on left side is obviously no mere accident, but is the expression of the slight predominance of the left hemisphere over the right. Somewhat greater are the distances to the end of the sylvian fissure in the two hemispheres. There is a tendency for the sylvian fissure to be longer on the left side, even where the right hemisphere is longer. This is in agreement with Cunningham's ( '92) observation. The differences in the distances of the two sides are again greater in whites than in negroes. Table 4 gives the percentage of the total horizontal length, of the chief divisions of the brain as marked by verticals through the midpoint of the central sulcus and the parietooccipital fissure. These percentages may not be strictly proportional to the sizes of the frontal, parietal, and occipital lobes, for the breadth is here not taken into account. In males the frontal region shows a somewhat larger percentage in whites than in negroes, while the parietal region is relatively larger in negroes. I n the small group of females the parietal region in negroes is again slightly larger, though this is also true for the frontal. As shown in table 1, however, the average frontal breadth of the female negro brain is almost a centimeter less than in white male. The occipital 489 ANTHROPOLOGY OF THE BRAIN region as measured by the projectional distance between the parieto-occipital fissure and the occipital pole h a s a greater percentage size in whites than in negroes, and with the exception of the rather heterogeneous group of miscellaneous whites, the right occipital region gives a slightly larger per cent than the left. It is of interest to compare this result with that of Cohn and Papez ('30), who found a greater TABLE 4 I l I i l 1 PKR CENT OI ROBIEONTAL LENOTH 1 Right 1 Left - ___ ___ ___ 14.5 46.4 46.1 38.9 39.3 14.6 2.30 2.27 3.20 2.81 3.26 2.30 76.7 2.08 76.9 3.27 Right I Left ! Right \ Left I Right 1 Left Males ~ Negro 37 White (German) 36 47.2 3.0 35.3 47.9 2.61 3.8- 35.0 3.16 17.4 3.11 17.1 2.50 78.9 1.68 78.7 2.30 M iscellaiieoua whites 18 47.2 2.33 47.7 3.44 36.6 2.44 35.7 3.83 16.2 2.08 16.5 2.01 78.2 2.69 77.7 2.55 Malay (Filipino) 10 47.2 2.26 49.4 2.21 37.2 3.50 36.0 2.95 15.6 3.18 14.6 1.43 78.2 1.85 7i.7 1.84 48.1 38.2 2.00 1.63 38.6 2.60 47.0 3.20 37.7 3.50 Negro 9 M j 47.9 Females -_ _ 13.9 2.74 13.2 3.00 75.0 2.20 75.2 2.36 15.9 2.40 15.2 2.20 76.7 2.19 76.8 2.99 White (Germaii) 10 37.6 3.00 length of the calcarine fissure on the right side than on the left. With regard to the temporal-occipital lobes, only fractional differences exist when expressed as a percentage of horizontal length. More significant is the difference between males and females of the respective races. As already pointed out, they a r e relatively smaller in the female brain. I n comparing head size and skull capacity in males and females, HrdliEka ('25) observed that in males the cranial 490 C. J. CONNOLLY capacity is 98.5 to 107 per cent of the cephalic module, while in females it is only 87 to 94.5 per cent of the module. The smaller relative size of the temporal-occipital lobes would seem to be a factor in explaining this difference. But our series of female brains is rather small to afford conclusive evidence on this point. SUMMARY 1. An apparatus, used in this investigation, is described which the writer believes would help standardize brain measurements. 2. The study of the 240 hemispheres of the 120 brains reveals that the left hemisphere is longer in a larger percentage of cases than the right, especially in whites, yet the differences are quite small on the average. I n negro males the right hemisphere was longer in 32.4 per cent and the left longer in 40.5 per cent. I n whites (German) the right was longer in 30.5 per cent and the left longer in 58.3 per cent. I n the whole series of 120 brains, male and female, the right hemisphere is longer in 31.7 per cent, the left longer in 50.0 per cent, and the hemispheres are equal in 18.3 per cent. 3. The slight predominance of the left hemisphere over the right is also revealed in the greater average projectional distance from the frontal pole to the central sulcus, to the parieto-occipital fissure and to the sylvian fissure of the left side. The left temporal-occipital diameter is, on the average, likewise greater than the right. 4. The brain weights correspond fairly closely with the size dimensions in the respective races. 5. The brain can be recognized by observation in a considerable percentage of cases as belonging to a male or a female, and the averages of certain dimensions confirm this (e.g., frontal-height index). Further, in correlation with average brain weight, practically all dimensions are slightly smaller in females than in males. 6. Comparing the two large groups of whites and negroes, while the variability is large and there is much overlapping, ANTHROPOLOGY O F THE BRAIN 491 the mean values reveal definite differences. The dimensions correlate well with what we might expect from a knowledge of the cranium in the two races. The negro brain is on the average relatively longer, narrower, and flatter than the brain of whites. 7. The frontal region, as measured by the projectional distance to midpoint of central sulcus, is, relative to the total length of the brain, larger in male whites than in negroes, while the parietal is larger in negroes than in whites. I n the small group of females the frontal region does not show this excess in whites, though again the parietal is larger in negroes. 8. It is suggested that the difference in the relation of cranial capacity to cephalic module in males and females may be in part due to the relatively smaller temporal-occipital lobes in the latter. LITERATURE CITED B w m , H. 1921 Untersuchungen uber den Zellgehalt der menschenlichen Grosshirnrinde. Zeitsch. ges. Neurol. u. Psych., LXIX. BETHE,A. 1925 Zur Statist& der Links- und Rechtshandigkeit und der Vorherrschaft einer Hemisphare. D. med. Woch., Nr. 17. BUSHYAKIN, N. 1928 Characteristics of the brain of the Mongol race. Am. J. Phys. Anthrop., XII, no. 2. COHN, H., AND J. W. PAPEZ1930 A comparative study of the visuosensory or striate area in the two hemispheres of the human brain. Am. J. Phys. Anthrop., XV, no. 1. CUNNINGHAM, D. J. 1892 Contributions to the surface anatomy of the cerebral hemispheres. ‘‘ Cunningham Memoirs, ” Roy. Irish Acad. Dublin, no. VII. HRDLICKA, ALES 1901 An Eskimo brain. New York. 1907 Measurements of the cranial fossae. Proc. U. S. Nat. Museum, X X X I I I . 1920 Anthropometry. The Wistar Institute, Phila. 1925 Relation of the size of the head and skull to capacity i n the two sexes. Am. J. Phys. Anthrop., VIII, no. 3. JACOBI, A. 1927 Anatomie und Histologie des Qrosshirns, I. Leipzig. JAEOFJL, R. 1914 Inhaltsberechnung der Rindensubstanz. Arch. Psych. u. Nervenkrankheiten, LIV. RAPPERS, AR.IENS 1927 Indices for the anthropology of the brain applied to Chinese, dolicho- and brachycephalic Dutch. Proc. K. Akad. Wet. Amsterdam, XXX, no. 1. LANDAU,E. 1923 Anatomie des Grosshirns. Bern. RETZIUS,G. 1898 Das Menschenhirn.