In the third frontal convolution are situated Broca's centres, which are believed to be the seat of articulate speech; while along Rolando's fissure, in the ascendant convolutions, is the locality designated by physiologists as the motor centres.

The occipital lobe is the location of the zone of sight; and the temporal lobe, that of hearing.

It is important for us to observe the volume of the brain, and therefore that of the head, in relation to the rest of the body; it is enormous in the embryo; and even at birth and during childhood the head is quite voluminous as compared with the body, as appears from the diagram in Fig. 16, in which a new-born child and an adult man are reduced to the same scale, each retaining his relative bodily proportions. In Fig. 22 a new-born child is shown in two positions: from the front and from behind; the head is very large and the cranial nodules are plainly visible. Figs. 80 and 81 represent the same child at the age of six months and a year and a half; in the first picture the head is still very large as compared with the body, and the forehead protrudes (infantile forehead); in the second, the proportion between head and body has already altered.

A knowledge of the laws governing the growth of the brain is of particular importance in relation to pedagogic anthropology.

Within the last few years anthropologists have established certain principles that are well worthy of notice:

1. The child's head is normal when its volume and cephalic index come within the limits of normality (even if the shape appears abnormal: Simon, Binet, etc.).
2. When the volume of the head is too small it frequently indicates psychic deficiency; when it is too large, even up to the age of twenty years, it indicates a predisposition to precocious mortality (see below).

Very frequently when the size of the head is larger than normal and is not due to pathological causes (rickets, hydrocephaly, etc.), it is associated with an excessive development of the brain, and also with an intellectual precocity. A high percentage of this type die before reaching the age of twenty years; and this fact confirms the popular belief that children who are too intelligent or too good cannot live long.

This indication alone ought to be sufficient to prove the pedagogic importance of the cerebral volume.

The researches made by various authors in regard to the growth of the brain are not rigorously in accord as to the limits of volume: but they do agree as to the rhythm of growth.

Welcker gives the following figures:

WEIGHT OF THE BRAIN IN GRAMS
(According to Welcker)

Accordingly, the weight of the brain is doubled before the end of the first year; according to Massini it is very nearly doubled at the end of the first six months:

MASSINI'S FIGURES AS TO THE WEIGHT OF THE BRAIN

It follows from these figures that by the end of the sixth month the weight of the brain is already very nearly doubled; but the maximum growth takes place between the ages of one month and three, after which it shows a notable diminution of rate.

But while the weight of the whole body is increased threefold by the end of the first year, that of the brain is very far from being tripled, since the rate of growth is still further diminished during the second six months; in fact even according to Welcker the weight at the end of the first year has little more than doubled.

Accordingly the rhythm of cerebral growth is not identical with that of the increase in weight of the body taken as a whole.

According to Massini, the relation between the cerebral weight and the weight of the body, at the various successive ages, is as follows:

RELATION BETWEEN WEIGHT OF BRAIN AND TOTAL WEIGHT
(According to Massini)

In other words, the body grows more rapidly than the brain, and consequently, than the head: a fact which results in the different proportions already noted between head and body.

The rhythm of brain growth considered by itself has been set forth in a most noteworthy and accurate fashion by Boyd, based on the study of about two thousand cases; from the figures given by Boyd, I have calculated the amount of increase from period to period, as well as from year to year, the whole result being set forth in the following table:

RHYTHM OF GROWTH OF BRAIN
(Males: According to Boyd)

In the above table, the first column of figures gives the mean average weight of the brain, obtained by direct observation of individual subjects; while from all the others the rhythm of cerebral growth and involution throughout the successive periods of life may be computed.

We see that the maximum growth takes place in the first years of life, the intensity is greater in the first year than in the second, and greater in the first three months than in those that follow. Already at the end of the first year the brain has surpassed one-half of the maximum weight which the individual is destined to attain in adult life (last column: proportions computed on scale of 100). A notable rate of increase continues up to the age of four, after which it moderates, but receives a new impulse at about the fourteenth year (period of puberty); hence it appears that at this important epoch of life the brain not only shares the general rapid growth of the body, but that by the end of the fourteenth year the brain has already practically completed its development; in fact, assuming that 100 represents its complete development, the weight of the brain is already 95.3; and at thirty it will be only 99.3.

By studying the above table we can obtain a clear analysis of these phenomena.

For women, Boyd gives the following figures:

THE GROWTH OF THE BRAIN IN WOMEN
(Figures Given by Boyd)

The rhythm of growth of the female brain is analogous to that of the male, except for the more precocious attainment of the maximum weight, which corresponds to the more precocious evolution of the female organism.

It should be noted that in the tables above cited the maximum is actually 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)

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

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:

Figures given by Manouvrier:

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)

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

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)

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)

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)

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)

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 of the cranium another element enters in: the form. The cranial circumference of an extremely brachycephalic cranium (almost circular) may contain a larger surface (and consequently include a larger volume), than a maximum circumference of the same identical measure, which belongs to an extremely dolichocephalic cranium (approaching the shape of an elongated ellipse). This may be easily understood if we imagine a loop of thread laid out in the form of a circle: if we pull it from two opposite sides, the enclosed area diminishes until it finally disappears as the two halves of the thread close together, while the length of the thread itself remains unaltered.

Nevertheless, the maximum circumference still remains the linear index best adapted to represent the volume; indeed, the authorities take its proportional relation to the stature as representing the reciprocal degree of development between head and body at the different successive ages.

Here are the figures which Daffner gives in this connection:

DEVELOPMENT OF THE STATURE AND OF THE CEPHALIC PERIMETER FROM BIRTH TO THE AGE OF ELEVEN YEARS

DEVELOPMENT OF THE STATURE AND OF THE CEPHALIC PERIMETER BETWEEN THE YEARS OF 13 AND 22

One very important research made by Daffner is in reference to the maximums and minimums that are normal for each successive age. This is extremely useful for the purpose of diagnosing the morphological normality in relation to the age. He naturally bases his figures upon subjects studied by him personally, who altogether form an aggregate number of 2,230, and are not always sufficiently numerous when distributed according to their ages. Nevertheless, in the great majority of groups, especially those including the younger children, the number of subjects is sufficient and even superabundant.

At all events, Daffner's researches may serve as a valuable guide in the researches that lay the foundation for diagnosis; and every future investigator will find it an easier task, under such guidance, to make his own contribution to it and to correct those inaccuracies which (for certain epochs) are to be attributed to an insufficient number of subjects.

Daffner distinguishes, for each year, a maximum and a minimum both for the stature and for the cephalic perimeter; but since the person having the maximum stature does not always have the maximum cephalic perimeter, and vice versa, the author indicates, in connection with the maximum and minimum figures, the other of the two measurements which, as a matter of fact, corresponds to them in each given case.

INDIVIDUAL VARIATIONS

MAXIMUMS AND MINIMUMS OF STATURE AND OF CRANIAL CIRCUMFERENCE

FEMALES FROM BIRTH TO THE AGE OF ELEVEN YEARS

EXTREMES BETWEEN THE AGES OF 13 AND 22 YEARS
(The figures here given are less exact, because of the great scarcity of subjects)

Nomenclature Relating to Cranial Volume. Anomalies.—(In regard to the method of directly measuring or calculating the cranial capacity, and of taking and estimating the measurements of the skull, see the section on Technique.)

Limits.—The cranial capacity, according to Deniker, has normally such a wide range of oscillation that the minimum is fully doubled by the maximum, the limits being respectively 1,100 and 2,200 cubic centimetres—these figures, however, including men of genius. Furthermore, the mean average capacity oscillates between limits that change according to race—not only because the cerebral volume may of itself constitute an ethnic characteristic (superior and inferior races) with which the form of the forehead is usually associated, but also because the cranial volume bears a certain relation to the stature, which is another factor that varies with the race.

Deniker gives the following mean averages of oscillations:

The average difference of cranial capacity is 150 cubic centimetres less in woman than in man.

The following nomenclature for oscillations in cranial capacity was established by Topinard, based upon the figures and methods of Broca:

To-day, however, the terms macrocephalic and microcephalic have come to be reserved for pathological cases. Virchow has introduced the term nanocephalic to designate normal crania of very small dimensions; while Sergi has adopted a binomial nomenclature, calling them eumetopic microcephalics, which signifies possessed of a fine forehead: since, as we have seen, it is precisely the shape of the forehead which determines normality. And in place of macrocephalic, we have for very large normal crania the new term megalocephalic.

Pathological terminology includes the following nomenclature: macrocephaly, sub-macrocephaly, submicrocephaly, microcephaly.

Microcephaly may fall as low as 800 cubic centimetres; macrocephaly may rise as high as 3,000 cubic centimetres, and at these extremes the volume alone is sufficient to denote the anomaly. But in many cases the volume may fall within the limits of normality; in such cases it is the pathological form and an examination of the patient which lead to the use of the term submicrocephalic in preference to that of nanocephalic, etc.

The volume, taken by itself, if it is not at one of the extreme limits, is not sufficient to justify a verdict of abnormality.

The terms macro- and microcephalic are, in any case, quite generic, and simply indicate a morphological anomaly, which may include many widely different cases, such, for example, as rickets, hydrocephaly, pachycephaly, etc., all of which have in common the morphological characteristic of macrocephaly.

In rickets, for instance, macrocephaly may occur in conjunction with a normal or even supernormal intelligence (Leopardi). Microcephaly, on the contrary, could never occur combined with normal intelligence, since it is a sign indicative of atrophy of the cerebro-spinal axis and diminution or, as Brugia phrases it, dehumanization of the individuality.