Pedagogical Anthropology, Maria Montessori [online e book reader TXT] 📗

given as occurring at the age of twenty; and that after this period the weight diminishes again, subsequently increasing up to an age that varies according to the sex. But this maximum at the age of twenty must be considered as one of the false results of mean averages; and it must be explained on the ground that after the twentieth year the death rate has eliminated a series of individuals whose heads were abnormally large, and that a majority of the survivors were those whose heads had developed within normal limits.

This fact is further confirmed by Wagner's figures, cited by Broca:

MEAN WEIGHT OF THE BRAIN
(According TO Wagner)

Age Men Women Under 10 years 985 1,033 From 11 to 20 years 1,465 1,285 From 21 to 30 years 1,341 1,249 From 31 to 40 years 1,410 1,262 From 41 to 50 years 1,391 1,261 From 51 to 60 years 1,341 1,236 Above 60 years 1,326 1,203

Here again we have a false maximum at twenty, which nature subsequently corrects through mortality.

From such knowledge we obtain certain important rules of hygiene.

The normal brain which exceeds the common limits of volume is not, in an absolute sense, incompatible with life. We need only to call to mind certain men of genius who had the brains of a giant.

Accordingly a brain which exceeds the limits demands of the individual who possesses it that he shall live according to certain special rules of hygiene. Children and young people who are too intelligent, too good, in other words, children of the elite class demand a special treatment, just as much as any other class of beings that pass beyond the bounds of average normality. Parents and teachers ought to be enlightened in regard to these scientific principles; the growth of individuals who are exceptional in regard to their intelligence and their emotions, should be supervised as though it were something precious and fragile. Such individuals are destined to be more subject than others to infective maladies, which frequently prove fatal, developing symptoms of meningitis and cerebral affections. Consequently a hygienic life, psychic repose, an avoidance of emotional excitement, moderate physical exercise in farm or garden, a prolonged stay in the open country, might be the salvation of children of this type, who often are over-praised and over-stimulated by friends and relatives, and consequently subjected to continual excitement and surménage to a degree destructive to their health.

Extreme Individual Variations of the Volume of the Brain.—In regard to individual variations, the authorities give various figures, from which the following have been selected as most noteworthy for their accuracy of research:

NORMAL EXTREMES OF INDIVIDUAL VARIATIONS IN THE VOLUME OF THE BRAIN

Authors Age: from 20 to 60 years From 60 to 90 Maximum Minimum Maximum Minimum Calori 1,542 1,024 1,485 1,080 Bischoff 1,678 1,069 1,665 1,080 Without distinction of age: Broca Maximum
1,830 Minimum
1,049

These figures refer to individuals belonging to European races.

Comparison with the Brains of Apes.—The brain of the great anthropoid apes (Chimpanzee, Orang-utan, Gorilla), whose total weight of body is comparable to that of man, weighs on an average 360 grams, and the greatest weight which it can attain is 420 gr.

Specific Gravity of the Human Brain.—In normal individuals, the average specific gravity is 1.03; in insane persons it is slightly higher: 1.04.

The Relation between the Weight of the Brain and the Cranial Capacity: Figures given by Lebon:

Weight of the brain in grams Cranial capacity in cubic centimetres 1,450 1,650 1,350 1,550 1,250 1,450 1,150 1,350

Figures given by Manouvrier:

Weight of the brain in grams Cranial capacity in cubic centimetres 1,700 1,949 1,450 1,663 1,250 1,432 1,000 1,147

Increase in the Volume of the Brain.—Studies regarding the growth of the head, although not yet complete, have gone sufficiently far to give us some useful ideas. In regard to the volume in a general sense, the cranium in its growth obeys the cerebral rhythm.

We shall speak in the section on Technique of the methods of measuring the head: at present it will suffice to point out that the measurements may be made directly upon the cranium, and the cranial capacity calculated directly from the head: and that the maximum linear measurements are sufficient to indicate the volume—such measurements being the three maximum diameters, longitudinal, transverse, and vertical, and the maximum circumference. Even the forehead, as an index of the general volume of the brain, is of interest in researches relating to the volumetric growth of the head.

Regarding the growth of the several cranial dimensions, the most accurate and complete knowledge is furnished by Binet's researches among the school-children of Paris (1902).

This author has made special investigations into the rhythm of growth of the cranium and of the face, with special reference to the period of puberty. The following are the mean averages obtained by him, relative to the three diameters corresponding to the three maximum dimensions of the head:

MEAN AVERAGES OF CEPHALIC MEASUREMENTS TAKEN UPON CHILDREN OF DIFFERENT AGES
(Binet: From the schools of Paris)

Measurement Kindergartens Lower primary schools Upper primary schools Normal schools 4 years 5 years 8 years 10 years 12 years 14 years 14 years 16 years 18 years Antero-post. diameter 169.5 173.9 174.7 177.1 181.5 181.5 185.3 188.3 190.4 Transverse diameter 140.6 141.7 145 145.7 147.9 150.1 155.5 152.3 156.7 Vertical diameter 118.8 121.6 122 122.8 127.6 129.7 128.1 131.4 130.8

It is evident that these figures contain inaccuracies, especially in regard to the vertical diameter (where the subsequent two-year period gives a smaller measurement than the preceding) due to the fact that the averages were obtained from an insufficient number of subjects or from subjects differing too widely in intelligence (from schools of different grades). For this reason Binet summarises the differences in growth, that is, the increase in relation to the diameters, under broad groups (six year groups, from four to ten years, and from ten to sixteen), in order to determine whether puberty exerts a sensible influence upon the cranial growth. The result is contained in the following table:

INCREASE OF THE THREE MAXIMUM DIAMETERS OF THE HEAD IN MILLIMETRES FROM FOUR TO EIGHTEEN YEARS OF AGE

Age in years: from — to — 4-6; 6-8; 8-10 10-12; 12-14; 14-16 16-18 Antero-posterior diameter 5.6; 0.8; 2.4 4.4; 1.8; 5 2.1 8.8 11.2 Transverse diameter 1.1; 3.3; 0.7 2.2; 3.9; 0.5 4.4 5.1 6.6 Vertical diameter 2.8; 0.4; 0.8 4.8; 2.3; 2.5 0.6 4.0 9.6

From which it appears that there exists, in regard to the head, a puberal acceleration of growth.

These conclusions of Binet are indirectly confirmed by the researches of Vitale Vitali regarding the development of the forehead in school-children; since it is well known that the forehead represents the index of the general growth of the cerebral cranium.

Vitale Vitali based his observations upon school-children and students between the ages of ten and twenty. He not only measured the width of the forehead (frontal diameter; see Technique), but also measured its height, obtaining the percentage of its relation to the width (frontal index).

These are his figures:

FRONTAL INDEX AND DIAMETER ACCORDING TO AGE

(Vitale Vitali: Researches Among Scholars and Students From 10 To 20 Years Old)

Age Frontal index Frontal diameter Amount of increase 11 years 73.05 107.5 — 12 years 74.11 112.0 4.5 13 years 74.14 112.5 0.5 14 years 74.80 114.4 1.9 15 years 75.67 116.8 2.4 16 years 77.24 120.1 3.3 17 years 77.02 120.6 0.5 18 years 77.36 121.5 0.9 19 years 77.60 122.8 1.3 20 years 77.15 122.1 0.7

Accordingly, between the years of fourteen and sixteen there is a puberal acceleration of growth, accompanied by an elevation of the forehead (high frontal index).

Vitali gives, as extreme limits of the frontal index, 68 and 83.

But in order to give a better illustration of the author's figures, his own words may be quoted: "It appears from our observations that the forehead begins to develop in notable proportions during the fourteenth year, and that the development of the frontal region as compared with the parietal region continues to augment up to the sixteenth year; after this it still increases, but only by a few millimetres, until the end of the sixteenth year. The cephalic development is completed between the sixteenth and eighteenth years. This observed fact is of great importance in relation to the development of the intellect."

The most complete figures at the present time on the growth of the brain, are those of Quétélet, which follow its development from birth until the fortieth year. They are summarised in the following table:

INCREASE IN THE CIRCUMFERENCE OF THE BRAIN AND IN ITS THREE MAXIMUM DIAMETERS
(According to Quétélet)

Age Circumference in millimetres Maximum diameters Antero-post. Transverse Vertical Men Women Men Women Men Women Men Women At birth 335 335 120 120 100 100 80 80 1 year 440 439 158 157 127 126 105 105 2 years 471 469 168 167 135 134 113 113 3 years 486 483 171 170 137 136 117 115 4 years 496 493 174 173 138 137 119 116 5 years 503 500 176 175 139 138 120 117 6 years 508 505 178 177 140 139 121 117 7 years 513 509 179 178 142 140 122 118 8 years 519 512 180 179 143 141 123 118 9 years 523 515 181 180 144 141 124 119 10 years 527 517 182 180 145 142 125 119 11 years 531 518 183 181 146 142 126 120 12 years 535 519 184 181 147 143 127 121 13 years 539 520 185 182 147 143 128 122 14 years 543 521 186 182 148 144 129 123 15 years 547 523 186 183 149 144 130 124 16 years 551 525 187 183 150 145 130 125 17 years 555 528 188 184 151 145 130 125 18 years 561 531 189 184 152 146 131 126 19 years 563 533 190 185 153 146 131 126 20 years 564 535 191 185 153 147 131 126 25 years 564 537 191 186 153 147 131 127 30 years 564 538 191 186 153 147 131 127 40 years 564 538 191 186 153 147 131 127

It appears from the foregoing table that after the twenty-fifth year the growth of the cranium practically ceases in all directions. In regard to the rhythm of growth, the problem is rendered clearer by the following table, which gives the annual increase:

ANNUAL INCREASE IN THE MAXIMUM CRANIAL MEASUREMENTS IN MALES
(From Figures Given by Quétélet)

Age Circumference Antero-post. diameter Transverse diameter Vertical diameter 1 105 38 27 25 2 31 10 8 8 3 15 3 2 4 4 10 3 1 2 5 7 2 2 1 6 5 2 1 1 7 5 1 1 1 8 6 1 1 1 9 4 1 1 1 10 4 1 1 1 11 4 1 1 1 12 4 1 1 1 13 4 1 1 1 14 4 1 1 1 15 4 1 1 1 16 4 1 1 1 17 4 1 1 1 18 4 1 1 1 19 4 1 1 1 20 1 1 1 1

It appears from the above table that the total growth of the cranium takes place to a notable extent during the early years of life; as regards the diameters, the longitudinal diameter grows faster during the first few months than the transverse; but after the first year, the two maximum diameters which determine the cephalic index increase in very nearly the same proportion (constancy of the cephalic index throughout life). The vertical diameter on the contrary undergoes a relatively much greater increase than the two others, since, although much shorter than the transverse, it nevertheless overtakes and surpasses it in its absolute annual increase.

This corresponds to the fact that the first two diameters are indexes of growth relative to the base of the cranium, while the vertical diameter is the index of expansion of the cranial vault, which more directly follows the growth of the brain and elevates the forehead as it pushes upward.

Quétélet's figures, however, fail to show in the rhythm of growth that puberal acceleration which has been observed to take place in the growth of the brain. This contradicts the researches of Vitali and also those of Binet.

Similar studies have been made a number of times during the last few years, especially in America, but with English tables of measurement, and with little uniformity in the results obtained by the different investigators.

Among the most recent and most complete figures should be cited those of Bonnifay[38] in which however the measurement of the vertical diameter is lacking, or in other words the third element needed, in conjunction with the dimensions of length and breadth, to give the volumetric factors.

CRANIAL MEASUREMENTS AT DIFFERENT AGES
(According to Bonnifay)

Age from — to — Absolute figures Amount of Increase Circumference Antero-posterior diameter Transverse diameter Circumference Antero-posterior diameter Transverse diameter Birth to 15 days 343.9 116.3 93.4 — — — 15 days to 2 months 368.7 126.3 99.1 24.8 10.0 5.7 3 months to 4 months 388.8 132.7 106.0 20.1 6.4 6.9 6 months to 1 year 429.8 145.4 118.2 41.0 12.7 12.2 1 year to 2 years 459.7 154.3 129.3 29.9 8.9 11.1 2 years to 3 years 473.5 161.9 133.3 13.8 7.6 4.0 3 years to 4 years 487.4 166.2 136.3 13.9 4.3 3.0 4 years to 5 years 495.7 169.9 138.3 8.3 3.7 2.0 5 years to 6 years 497.8 171.9 140.4 2.1 2.0 2.1 6 years to 7 years 504.4 172.8 141.1 6.6 0.9 0.7 7 years to 8 years 511.6 175.2 143.7 7.2 2.4 2.6 8 years to 9 years 514.1 176.1 144.3 2.5 0.9 0.6 9 years to 10 years 514.7 176.4 144.2 0.6 0.3 0.9 10 years to 11 years 519.8 177.1 146.6 5.1 0.7 2.3 11 years to 12 years 521.1 177.5 145.7 1.3 0.4 0.1 12 years to 13 years 529.7 180.1 147.8 8.6 2.6 1.2 13 years to 14 years 533.1 178.1 148.5 3.4 — 0.7 14 years to 17 years 548.8 182.4 152.2 15.7 2.3 3.7 22 years to 27 years 549.1 186.6 153.2 0.3 4.2 1.0

Among the linear measurements of the cranium, the one which serves to give the most exact index of volume is the maximum circumference.

This index, nevertheless, is not a perfect one, in the same sense that the stature, for instance, is a perfect index in respect to the body, because in the case