Pedagogical Anthropology - Maria Montessori (best free novels TXT) 📗
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Fig. 41. Fig. 42. Dividing line in human skull, as compared with that of gorilla.
Fig. 43.—Rounded ellipsoidal cranium.
Fig. 44.—Brachycephalic cranium (vertical norm)
Fig. 45.—Remains of spy cranium.
Fig. 46.—Brachycephalic cranium.
Fig. 47.—Egyptian cranium, 21st dynasty, ovoid type.
Fig. 48.—Dolichocephalic cranium, from lateral norm.
But the failure of such attempts afforded additional proof of the fact that the volumetric development of the cranium depends upon the brain alone.
If a precocious or abnormal suture occurs in the cranial bones, there does not follow an arrest of development, but simply a malformation; which is precisely in proportion to the potentiality of the brain, which grows less where the suture has been formed, and in compensation grows more than normally where the conditions of the bones permit of cerebral expansion; and a deformity results. Microcephaly on the contrary shows inferiority of form (smallness, receding forehead, etc.), but not malformation.
Anomaly of form, therefore, results only from anomaly of skeletal development, and is frequently found in conjunction with a normal development of the brain.
Consequently malformations of the cranium do not have the grave significance of biological inferiority or of degeneration that they were at one time believed to have; but frequently they must be considered in connection with pathological conditions resulting for the most part in delayed development in the embryo or in early infancy, producing a thickening of the bone, or a partial suturation of the points, or parts, or of the entire suture (punctiform synostosis, partial or total); sometimes the sutures remain unaltered, and the deformation must be attributed to various disturbances connected with the nutrition of the skeleton in the course of intrauterine evolution (hereditary syphilis, denutrition of the mother during pregnancy, etc.). In short, a cranium that is abnormal in form is an indication of pathological occurrences or of physiological errors that have resulted in altering the normal growth of the individual.
There are many anomalies in the form of the cranium, but here we will cite only the two principal ones, because they are the most frequent and most likely to be encountered in individuals whose growth has been retarded (from lack of nutrition) and consequently constitute signs of physiological inferiority often associated with social caste. These two forms are: scaphocephaly and plagiocephaly.
The scaphocephalic cranium (Figs. 51, 52), is characterised by being very narrow and flattened laterally; while the forehead and the occiput project in front and behind, the two parietal bones meet above almost in an angle, so that, if it were turned upside down, the vault of the cranium would have the appearance of the hull of a ship.
The plagiocephalic cranium is a cranium which is unsymmetrical in respect to its longitudinal axis; that is, it is not equally developed on the right and on the left.
As a matter of fact, our bilateral symmetry is an ideal standard rather than an absolutely attainable reality; we are all of us a little larger on one side and a little smaller on the other, but to so slight a degree as to escape superficial observation, so that in general we have apparently a bilateral symmetry—that is, we appear to be symmetrical according to the testimony of our senses; but a more delicate examination proves that this is not true. Plagiocephaly therefore represents an exaggerated case of a normal fact. Plagiocephaly may be simple or compound; it is simple when the asymmetry is partial; namely, when it is confined to the anterior or posterior portion; it is compound when it is total; and in such case we find a complete diagonal correspondence: for instance, if the right nodule in the frontal region is more prominent, the left nodule is more prominent in the left occipital region, or vice versa. In general it may be said that the various forms of plagiocephaly are produced by asymmetry of the nodules or of the flattened surfaces of the cranium. Even in the case of microcephaly and of macrocephaly, which are substantially anomalies of volume, we find corresponding characteristic abnormalities of form. The microcephalic cranium is of inferior type, suggesting that of the ape—in other words, it is a cranium which has mechanically adapted itself to a brain of inferior volume: the macrocephalic cranium, especially if the abnormality is due to rickets or to hydrocephaly, calls to mind the infantile type of cranium; it has the characteristic bulging forehead, while mechanical adaptation frequently renders it very round (pathological brachycephaly). We will take up this question again when we come to speak in particular of malformations and to describe the technical methods of cranioscopy. What more particularly concerns us now is a consideration of the normal form of the cranium and its morphological evolution.
Fig. 49.—Cranium of new-born child (lateral norm).
Fig. 50.—Cranium of new-born child (vertical norm).
Fig. 51. Fig. 52.
Scaphocephalic cranium.
Fig. 53.—Cranium of new-born child seen from above, showing polyhedric contour due to nodules of ossification; fontanelle of the bregma; and suture dividing the two frontal bones.
Fig. 54.—Ellipsoides (classified by Sergi).
The Morphological Evolution of the Cranium through the Different Periods of Life. Embryogeny. Order of Appearance of the Points of Ossification and of Synostosis of the Sutures.—In its successive transitions through the different periods of life, the cranium not only acquires successively greater volume, but it assumes forms corresponding to the different grades of morphological evolution. We may group its transformation under five different periods: 1. from conception until birth (embryonic evolution); 2. from birth until the end of the third year (infantile evolution); 3. from three years old until twenty (youthful evolution); 4. from twenty to forty (adult age); 5. from forty to the end of life (involution).
First Period.—In the earliest stages of intrauterine life the cranium consists of a membranous skin, enclosing the primitive cells of nerve tissue constituting the brain; it has a cartilaginous basal part, destined later to form the base of the skull (basioccipital and basisphenoid bones). But all the rest (the vault or cap of the cranium) remains in a membranous state, so that at this period the head of the embryo has not yet acquired a definite form.
Fig. 55.—Cranium of new-born child. Showing nodules and fontanelles.
In the second month of intrauterine life the phenomena of ossification have already begun to take place; that is, a fine network has formed, spreading over almost the entire surface, which proceeds to fill up its interstices with calcareous salts. This process, however, is more rapid and more intense at certain points (points of ossification), from which it cannot properly be said that the ossification radiates, but rather that at these points the general process is intensified and concentrated. There are five principal points of ossification: two frontal, two parietal and one occipital, which appear clearly defined and projecting like nodules, imparting to the cranium, when seen from above, a pentagonal form, which is the normal form of the infant cranium.
Second Period.—At birth the cranium has not yet completed the process of ossification, nor are the normal number of bones that will eventually compose the adult cranium, as yet definitely determined. Therefore the cranium of the new-born child has three distinct characteristics:
It is not yet uniformly rounded, but polyhedral because of the noticeable prominence of the five primitive nodules or centres of ossification (2 frontal, 2 parietal, 1 occipital, Figs. 53, 55). Since the process of ossification of the bones is not yet completed, certain membranous portions or cranial fontanelles still remain, which are especially wide at the points where several bones meet. The principal fontanelle is that of the bregma (at the juncture of the two frontal with the two parietal bones, quadrangular). Next comes that of the lambda, which is much smaller (juncture of the two parietal bones with the occipital, triangular), and lastly the fontanelles of the asterion and the pterion, on opposite sides of the temporal bones, the former being situated behind and the latter in front. Since the process of ossification is incomplete, the fusion of bony portions into entire bones, such as they are destined to be when complete development is reached, has not yet been accomplished; that is to say, certain bones of the cranium are still divided into several portions. For example, the frontal bone in the new-born child is composed of two bones, separated by a longitudinal suture that is destined to disappear, and the occipital bone is composed of four parts, namely, the base, the squama and the two condyles (basioccipital, exoccipital and superoccipital bones).During the first period of three years, while the brain is increasing notably and rapidly in volume, the cranium undergoes various and interesting transformations. The pentagonal form of the cranium tends steadily to become rounder, because the primitive nodules are diminishing, or even disappear, although in this regard many individual varieties result; and the processes of ossification reach their completion. This is the most important period of growth, during which the individual development of the perfect cranial form may be attained, provided the rhythm of growth between the brain and its envelope remains harmonious; or again, certain deformations may be definitely established, owing to the intervention of some pathological condition or a disturbance of nutrition, altering either the internal volume or the normal process of ossification of the bony covering.
The first closing of the fontanelles takes place, in our race, in those of the asterion (posterior to the temporal bones), and next in those of the pterion; and it sometimes happens, as an anomaly of growth that leaves no external trace in the living man, that a little bone is formed, duplicating the shape of the fontanelle itself; such little bones, very common in abnormal crania, are called Wormian bones. They may occur in connection with any of the fontanelles, but especially with that of the bregma.
Fig. 56.—Cranium of adult with abnormal medio-frontal suture.
The fontanelle of the lambda generally closes during the first year; and the last of all the fontanelles to close is the largest, which is situated toward the front of the head, at the bregma, and is well known, even by the common people, and can easily be felt upon a child's head; it generally closes toward the end of the second year; and its characteristics may furnish valuable indications of abnormality or insufficiency of the child's development. For example, if it diminishes and disappears ahead of time, this may constitute the first symptom of microcephaly, or at all events, of submicrocephaly (i.e., a case of microcephaly that is not very pronounced). On the contrary, when this fontanelle remains dilated and delays its normal closing, this is a sign of organic weakness and debilitating disease (cachexia, rickets, myxedema). Furthermore, the fontanelle in question may alter its characteristic appearance in certain forms of sickness. In the case of hydrocephaly it becomes distended, while in enteritis, on the contrary, in which the organism parts with a large proportion of liquid, it becomes depressed.
The sutures also undergo notable changes during this period of life. The first to become effaced is the metopic or medio-frontal suture, which is destined to close and form a single bone; by the end of the first year it is obliterated throughout the middle third of its length, and thereafter the process of suturation spreads upward and downward until it is completed at the end of the second year (Welcker, Haeckel, Humphry). Sometimes, however, this suture is not
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