Pedagogical Anthropology - Maria Montessori (best free novels TXT) 📗
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During this same time a fusion has also taken place between the occipital squama and the two lateral or condyloid portions; but the resultant whole still remains separated from the corpus or base of the occipital bone, which will not become welded into one solid piece with the rest before the age of seven years.
At the age of three, the ossification of the cranial vault has been completed. In place of being depressed and protuberant, as it was at birth, the cranium has grown upward and forward in the frontal region, assuming an almost definitive form; the volume of the cranium has at the same time undergone an exceedingly rapid growth, attaining proportions very near to those of an adult.
From the age of three onward the head grows slowly, and its transformations are much slighter and fewer. The cranial capacity which at birth is 415 cubic centimetres, becomes at the age of three, 1,200, at the age of fifteen, 1,393, and in the adult, 1,400 cu. cm. respectively. Accordingly we might say that at the age of three a sort of repose has been established in the growth both of the the brain and of the cranium; this is the age at which an awakening begins in the child of that intelligence which is to put him in touch with the external world, and it is also the age at which he may begin his education in school.
Third Period.—There follows a slow and parallel growth of both brain and cranium. The ossification of the cranium itself reaches completion. At the age of seven the occipital is definitely solidified into a single bone and between the years of fifteen and twenty the body of the sphenoid also becomes welded to the occiput. This process of synostosis begins from the interior of the cranium, and only subsequently manifests itself externally. Consequently, the basilar suture closes at the time when the last large molars, the so-called "wisdom teeth," appear. After this period, the base of the cranium can no longer undergo any sort of growth, and in the case of uneducated persons the complete development of the cranium is definitely accomplished.
Fourth Period.—But in the case of cultured persons, those who form the class of brain-workers, the brain continues to grow, although extremely slowly, up to the age of thirty-five or even forty, thanks to the sutures which still remain completely intact and which still make an expansion of the bony envelope possible.
After this comes the beginning of the
Fifth Period.—The period of involution, during which the synostosis (closing) of all the cranial sutures will successively occur, until in advanced old age the cranium becomes composed of a single bone, just as in the embryo it was formed of a single membrane.
The synostoses which occurred in the early periods had an evolutive significance and were associated with the growth of the body and the intelligence. These later synostoses, on the contrary, have an involutive significance and are associated with the physiological decay of the organism and at the same time with that of the psychic activities.
The first point at which synostosis takes place is in the region of the obelion, that is, near the middle of the suture which, unites the two parietal bones; shortly afterward, the fronto-parietal sutures begin to unite along the pterion. At the age of forty-five, the obeliac synostosis has progressed as far as the lambda, and that of the fronto-parietal suture to the bregma; and at fifty the ossification is very nearly accomplished, at least on the right-hand side (according to Broca's series of crania). At seventy the squama of the temporal bone unites with the parietal, and at eighty the entire cranium has become a single bone.
These processes are subject to no small number of individual variations; there have been cases of persons who, although very old, still preserved many of their cranial sutures intact and their psychic activities remained correspondingly alert (men of genius). Conversely, the closing of the sutures sometimes begins as early as the thirty-fifth year. A diagnosis of age, as determined by the skeleton, is consequently only approximate.
During the periods of growth the cranium may exhibit transitory anomalies; it is very common to encounter in the heads of children of the lower social classes, who are consequently subject to denutrition, malformations which represent various degrees and forms of plagiocephaly, and which subsequently disappear completely, as the development of the cranium advances. Anomalies of form must therefore be judged differently in the case of the child than in that of the adult.
It may even happen that the five primitive nodules persist for a long time and even remain as a definitive form of the adult cranium constituting, according to Sergi, a distinct variety, the pentagonal cranium. But this is quite rare. From the frequency with which this form is to be observed in schools attended by children of the poorer classes, it is better to regard it as due to a delay in morphological evolution, which will probably disappear later on.
Normal Forms of the CraniumWe are indebted to Sergi for an exact knowledge of the normal forms of the cranium. Such forms are racial characteristics and are invariable, as Sergi has succeeded in proving by a comparison of the most ancient forms of the cranium with recent forms. Accordingly this authority takes the cranial formation as the basis for his classification of races. We have no direct interest, so far as concerns the special scope of our own science, in the value of this theory of classification—a theory, by the way, already divined, although very imperfectly and under a different form, by French and German anthropologists. Sergi's studies of cranial forms interest us solely as a diagnostic test of normality as compared with abnormality. For it is due to these researches that certain forms that used to be considered pathological, have come to be recognised as normal.
The normal forms of the cranium may be grouped, according to Sergi, under nine primary varieties, each of which includes sub-varieties.
These nine varieties are named as follows:
I. Ellipsoid; II. Ovoid; III. Pentagonoid; IV. Rhomboid; V. Beloid; VI. Cuboid; VII. Sphenoid; VIII. Spheroid; IX. Platycephalic.
Fig. 57.—Ellipsoides depressus cranium.
I. Ellipsoid (Fig. 58).—This form is recognised by inspecting the cranium according to the vertical norm (see in the chapter on Technique the method of cranioscopy).
The cranial contour recalls an ellipse in which no trace of the nodules remains, and in which the occiput is not in the least flattened; while the anterior half of the cranium closely corresponds to the posterior half.
The sub-varieties are differentiated by their greater breadth and length, by the form and protrusion of the occiput, and also by the height of the cranium measured vertically.
Fig. 58.—Ellipsoid cranium.
Fig. 59.—Ovoid cranium.
Accordingly, the sub-varieties have a binominal nomenclature indicating, in addition to the fundamental characteristic (variety) the qualitative characteristic of the sub-variety (e.g., ellipsoids depressus; compare Fig. 57, showing a cranium seen laterally).
II. Ovoid.—This form of cranium, seen from above, is that of an ovoid, with the broader portion corresponding to the parietal bones, at the point where the characteristic embryonal nodules are situated. The protrusions of the parietal bones are apparent (swellings) but not angular (nodules). The occiput protrudes and is broad (Fig. 59).
Fig. 60.—Pentagonoid cranium.
Fig. 61.—Rhomboid cranium.
III. Pentagonoid.—In this form, persistent traces of the five primitive embryonal nodules are still plainly visible, giving the contour of the cranium, when seen vertically, the appearance of a pentagon. The protuberances, however, are quite smooth and not pointed, as in the embryonal cranium.
Fig. 62.—Beloid cranium.
IV. Rhomboid.—This form is similar to the pentagonoid, excepting that the parietal breadth is much more notable in proportion to the forehead, which is much narrowed and has lost its nodules.
Fig. 63.—Ovoids (classified by Sergi).
Fig. 64.—Pentagonoides acutus (Sergi's collection).
Fig. 65.—Beloides lybicus (classified by Sergi).
Fig. 66.—Platycephalus orbicularis (classified by Sergi).
Fig. 67.—Platycephalus ovoidalis (classified by Sergi).
Fig. 68.—Spheroidal cranium, vertical norm (Sergi's collection).
V. Beloid.—The beloid, or arrow-head cranium is like the ovoid with the occiput more flattened, so that the widest portion is further back than in the ovoid; toward the front it becomes narrower, constituting altogether an admirably shaped type of head.
Fig. 69.—Cuboid cranium.
VI. Cuboid.—This form is most clearly perceived when the cranium is seen either sidewise or from the rear. Not only the face, but the lateral and occipital walls as well are flattened; so also is the forehead, which in general is quite vertical.
VII. Sphenoid (cuneiform).—The broadening between the two parietal bones is usually far back and very evident, while the cranium narrows toward the front. The occiput is flattened.
Fig. 70.—Sphenoid cranium.
VIII. Spheroid.—Seen vertically, it presents the appearance of a very broad ellipse; all the curves tend to become spherical. The forehead, however, is not notably vertical.
IX. Platycephalic.—The fundamental characteristic of this type of cranium is that it is flattened on top, or rather, since such flattening cannot be absolute, the arch of its vault is a segment of a circle of very large diameter (Sergi), with the result that this cranium has the appearance of being very low vertically and very broad laterally. When seen vertically it may present a wide variety of contours, ellipsoid, ovoid, pentagonoid, etc., but its distinguishing characteristic remains that of the flattened vault.
Fig. 71.—Spheroid cranium.
Sub-varieties.—Sphenoids trapezoids, or trapezoid cranium. Observed from the vertical norm, this form appears as a variety of the sphenoid; and when seen laterally it is characterised by the lines of its contour forming a trapezium. Starting from the vertex of the cranium one line slants toward the forehead and another toward the occiput, which is very massive. In the figure given below, the quadrangle drawn in solid lines serves to indicate the correct position of the cranium, while the trapezium formed of dotted lines gives us its characteristic form.
Fig. 72.—Trapezoid cranium.
Among the forms described by Sergi, are several which were formerly held to be abnormal, such, for instance, as the platycephalic cranium and the pentagonoid. Similarly, when the surfaces of the cranium showed a tendency toward flatness, or when there were cranial protuberances, even though these were destined to disappear, they were regarded as malformations. Before this high authority offered us his guidance, there were certain forms, frequently encountered, that it was difficult to define, for example, the trapezoid cranium, which often presents a notable vertico-occipital flattening, with the vertex notably higher than the forehead.
There are also certain forms of cranium having the frontal region more restricted than the parietal region, or slanting down from a much elevated vertex, which have been proved to be normal forms; while still another error previously made was that of trying to judge the forehead on the criterion of a single model, deviations from which were much too readily relegated to the category of abnormalities. The most regular and beautiful forms, and the ones that are commonest in our racial stocks are the ellipsoid, ovoid and sphenoid. In my work on the women of Latium, precisely one of the points that I noted was the frequent occurrence of certain sub-varieties of the ellipsoid and the sphenoid.
In order to recognise the forms of the cranium, a certain training is necessary which each one must acquire for himself. Observations of the cranium will make it easier to judge of the form in relation to the head,
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