Head and Cranium
The term Head is applied to the living man; the Cranium, from which this branch of science takes its name, is the skeleton of the head. The cranium is composed of two parts, which may be virtually separated, in the lateral projection, by a straight line passing through the external orbital apophysis and extending to the auricular foramen, thus separating the facial from the cerebral portion of the cranium. Hence the cranium is the skeleton of the head in its entirety, and is divisible into the cerebral cranium and the facial cranium.
The Cranium.—The cranium is a complex union of a number of flat, curved bones united together by means of certain very complicated arborescent sutures, and forming a hollow osseous cavity of rounded form. I will briefly indicate the bones which form its external contour. On the anterior part is the frontal bone, terminated by the suture which unites it to the two parietal bones: the coronal suture; while the two parietal bones are joined together by the median or sagittal suture, which forms a sort of T with the other suture.
On the posterior side is the occipital bone, which is also joined to the two parietal bones, by means of the occipital or lambdoidal suture. Below the two parietal bones, in a lateral direction, are the two temporal bones; and between the temporal and parietal bones are situated the great wings of the sphenoid. The main body of the sphenoid is at the base of the cranium. Besides these there is another, internal bone, the ethmoid.
The Face.—The skeleton of the face is composed of fourteen bones; some of these are external and lend themselves to measurement; others which are internal and hidden contribute to the completion of the delicate scaffolding of this most important portion of the skeleton. The principal bones of the face are: the two zygomatic bones (articulating with the temporal, frontal and maxillary bones); the two nasal bones (articulating with the frontal and with the ascending branch of the maxillary, and uniting above to form the bridge of the nose; this is a bone of great importance in anthropology, because it determines the naso-frontal angle and the formation of the nose); the two upper maxillary bones, or upper jaw (articulating together in front to form the subnasal region; laterally with the zygomatic bones; above with the nasal bones; internally with each other, to form the palate, and posteriorly with the palatine bones); the mandible or lower jaw (a single bone, and the only movable bone in the cranium), articulating with the temporal bones by means of a condyle, and the separate parts of which are distinguished as the body of the mandible and the ascendant branches, which are united to the cranium.
Fig. 39.—Note the line of division between the cerebral and facial cranium; in addition to this the sutures are shown which divide the frontal, parietal, occipital and temporal bones. PD. Coronal Suture; DL. Sagittal Suture; AL. Lambdoidal Suture.
The bones of lesser importance, which are interior and hidden are: the two lacrymal bones (situated at the inner angle of the orbitary cavity), the vomer or osseous septum of the nose; the two bones in the nose which lie on each side of the vomer and are known as the turbinated bones (concha nasalis); and the two palate bones (which form the backward continuation of the palatine vault constituted by the maxillary bones).
Human Cranium and Animal Cranium.—The dividing line between the cerebral and facial cranium is of great importance in anthropology, because the relative proportions between these two parts of the cranium form a human characteristic, contrasting widely with the animal characteristics; and they offer a simple criterion for determining the higher or lower type of the human cranium. (Compare in this connection Fig. 40, skulls of the higher mammals and of man.)
Fig. 40.
The illustration represents a number of different animal skulls; and at the top are two human skulls, the one of an Australian and the other of a European. It will be seen that the proportions between the facial and cerebral portions are very different; in the animals, even in the higher orders such as the primates (orang-utan, gorilla, etc.), the facial and masticatory parts predominate over the cerebral.
One might even say that the skeleton gives us at a glance the characteristic psychological difference; the animal eats, man thinks; that is, the animal is destined only to vegetate, to feed itself; man is an entirely different species; he has a very different task before him; he is the creative being, who, through thought and labour, is destined to subjugate and transform the world.
There are still other characteristic differences between the animal and the human skull. The cerebral cranium of the ape is not only smaller but it is furnished with strong bony ridges, to serve as points of attachment for powerful muscles intended to protect the cranial cavity. The human skull is completely devoid of such ridges; it is perfectly smooth, with delicate contours; it might be described as "frail and naked"; for the word nakedness precisely expresses the absence of those defences with which the cranium of the anthropoid ape is so abundantly provided. Accordingly, the human cranium is undefended by soft tissues; and even the bony walls themselves are far from thick. If we take a transverse section of the bones of the cranium, we find that they are formed of two very thin layers of bone united by a porous, osseous substance; the external layer is in direct contact with the muscles of the scalp, and the internal layer with the brain. These two layers differ widely in their degree of elasticity: the external layer is so elastic that if it receives a bruising blow (provided this is not so heavy as to surpass its limits of elasticity) it will yield even to the point of touching the inner layer and then spring back to its original position without leaving any perceptible trace of the blow received (this is especially true in the case of infants),[36] while the inner layer is so unelastic as to appear almost as brittle as glass: so much so, for example, that the indirect shock of the same contusion may cause it to splinter into fragments, which may either penetrate the substance of the brain, or produce hemorrhages, or inflammatory reactions in the meninges—and sometimes may constitute the sole cause of epilepsy, and various forms of inflammation of the brain (even resulting in idiocy), and sometimes of meningitis and death.
Contusions on the heads of children, and in general blows resulting from falls or other causes, must be taken into serious consideration, in the history of the individual, even though they have left no profound traces externally.
This human characteristic of nakedness, of the absence of powerful bodily defences, is not limited to the head alone, but is diffused over the entire morphological organism. Man, considered as an animal, is weak; he is born naked and he remains naked, and destitute of those natural defences which explain the endurance and the survival of other species; neither the fur nor the plumage of mammals and of birds nor the bony shields of reptiles and scales of fishes serve as defences for this vertebrate, who has raised himself to the highest eminence in the zoological scale; neither the muscular strength and powerful teeth of the felines, nor the talons of the birds of prey have been his arms of conquest.
Nevertheless, man who has conquered the earth and overcome all his powerful biological enemies, owes his survival, equally with all other living creatures, to his victory over other animals and over his environment. Wherein lies the special strength of this little, feeble being, who has become the lord of the earth? It lies in his brain. The arms of this conqueror are wholly psychic. It is his intelligence which has prevailed over the might of other animals and enabled him to acquire the means of adapting himself to his environment, or else of adapting his environment to himself. His intelligence, which sufficed him as a weapon with which to achieve victory in the struggle for existence, is also the means which still permits him to continue on the road toward self-perfectionment.
The morphological importance attached by anthropologists to the cerebral cranium depends precisely upon this: that it is the envelope of the brain. If we examine the interior of the human cerebral cranium, we find that it has adapted its bony contours so faithfully to those of the soft tissues that it bears the imprint of the various parts of the brain (cerebrum, cerebellum), the convolutions, and even the blood-vessels of the meninges. Accordingly, a study of the cerebral cranium amounts to an indirect study of the brain itself.
Characteristics of the Human Cranium.—The characteristics of the human cranium are all associated with the great development of the volume of the brain. Let us assume that we have an elastic vessel, representing in form an animal cranium, open at the base through an orifice corresponding to the occipital foramen. If we inflate this vessel, it will not only begin to enlarge at the expense Of its folds (ridges), and to stretch and distend its walls (thinness and fragility of the cranial bones); but furthermore it will undergo a change in form, acquiring a more pronounced rotundity and pushing upward in its anterior part above the face. This part, rising erect above the face, and determined by the volume of the brain, is the forehead. Animals do not have an erect forehead; their orbits continue backward in an almost horizontal line, giving them an extremely receding brow. Corresponding to this preponderance of the cerebral portion, the facial portion retires below the brow, the mandibles do not extend beyond the anterior axis of the brain, and are so far diminished in volume that they assume, as compared with animals, a new function; in short, the mouth is no longer merely the organ of mastication, but also the organ of speech; its animal part has been spiritualised.
The Evolution of the Forehead.—Inferior Skull Caps; the Skull of the Pithecanthropus; the Skull of the Neanderthal Man. The forehead is so distinctly a human characteristic that mankind has not needed the help of anthropology in order to realise its importance—and as a sign of superiority, nobility or sovereignty, has placed upon the forehead the crown of laurel, or the crown of nobility or kingship.
Has the forehead always been a human characteristic, or have we acquired it little by little? Such a problem is associated with the evolution of the brain. There are in existence certain remains of the skeletons of primitive men, which show them to have possessed a cerebral cranium inferior in volume to that now attained by the human species; and in these remains the forehead is also profoundly different from that of to-day, in that it is much lower and slants backward, while the supraorbital arches are very prominent. Such is the evidence of the "cranial caps," discovered in the early geological strata.
In the tertiary strata of the island of Java, which in that remote epoch of the earth's history must, together with Sumatra, have formed part of the continent of Asia, which is considered as the "laboratory of races," a skull was found by Dubois which raised the problem whether it should be classed as that of an ape superior to those now existing, or of a primitive man. Prior to this discovery, it had been maintained that man did not make his appearance until the quaternary period. This supposed primitive man was called by his discoverer the Pithecanthropus, pithecanthropus erectus.
Remains that are unquestionably human occur in the quaternary period, in which however skeletons are very rare, as compared with relics of human labour or social life, relics which are found scattered everywhere throughout Asia and Europe as well (chipped flints). The various remains of skeletons show us skulls much inferior to those of modern man, but superior to that of the pithecanthropus. In treatises of general anthropology reproductions are given of human crania known as the Spy or Neanderthal type, belonging to the epoch when the gigantic mammoth still roamed the earth. The forehead is very low and receding and the orbital arches are enormously developed; while the cerebral capacity calculated from the cranial dimensions is inferior to that of modern man.
Consequently, as the brain increases in volume in the course of the revolution of the race, the cranium not only shows a corresponding volumetric increase, but at the same time alters its form, thus producing the forehead which little by little rises from a receding to an erect position, and becomes high where it was formerly low, while at the same time the prominent orbital arches disappear. Accordingly, we may consider the forehead as the skeletal index of the cerebral volume, and hence of the relative anthropological and intellectual superiority.
In addition to its above-mentioned value, it also furnishes us with a biological principle of much importance: the relation between the volume and form of the cranium.
While the volume has a significance that is relative to the mass of the body, the significance of the form is absolute.
Let us examine these two skulls: normal human skulls of our own epoch; one of the Celtic race (Fig. 46) and the other Sardinian (Fig. 43); that of the Celtic race is much larger and rounder; that of the Sardinian is very much smaller and more elongated.
If we were considering only the volume, we might say that it was simply a case of a microcephalic and a macrocephalic: two terms (microcephaly and macrocephaly) that fall within the province of pathology. On the contrary, these two skulls are normal, but they belonged to individuals characterized by differences of race; the one (small skull) having a low stature; the other (large skull) having a tall stature.
The volume of the head therefore bears a relation to that of the body; the volume has a relative significance. But the form in both of them reveals a state of normality; the two skulls have a high and erect forehead, and exhibit in their whole contour a fine and regular development. Therefore the form has an absolute significance. It even proves to us the normality of the volume, a fact which could not be determined by the volume alone.
Another mechanical correspondence between volume and form is disclosed when we compare the skull of a new-born child with that of an adult. The skull of the new-born child is much smaller in volume; but the form shows the relatively enormous volumetric development of the brain; in fact the skull is protuberant and the forehead bulges forward above the face (front bombé), while corresponding to this index of cerebral development is the enormous preponderance of the cerebral cranium over the facial cranium, which is so small as to be almost reduced to a simple rudiment.
Hence the form by itself alone reveals the infantile character of the cerebral volume, which, in relation to the bulk of the body is of far greater dimensions than in the adult. In fact, if a child simply increased in volume and its growth was not the sum total of a morphological evolution, the adult man would become a monster; his macrocephaly would be so exaggerated that his neck could not sustain the weight of the head (If the relations between the proportions in infancy were maintained through life the adult man would have a head with a perimeter of 130 centimetres, = 4 ft. 3 in.).
Aside from its mechanical relations to the volume, the form has characteristics dependent upon biological factors, such as the sex and the race. The female cranium in fact has a straighter forehead than the male and the orbital arches are absolutely wanting, while the entire surface of the cranium is smoother and more rounded.
Similarly, the different races exhibit forms determined by biological factors and not by mechanical causes—for instance, the degree of dolichocephaly (elongated cranium) and of brachycephaly (short cranium).
Hence the form is life's manifestation not only of the characteristics proper to the species, but also of the mechanical adaptations demanded by the material composing the body.
It may be said that the volume and the form of the cranium are dependent upon two different biological potentialities: the volume is mainly determined by the cerebral mass; the form, on the contrary, is mainly determined by the bony structure—no matter how completely form and volume coincide in their reciprocal mechanical relations.
That is, the attainment of a given volume of head depends upon the development of the brain; the bone follows this development passively, is the index of it, the skeletal representation of it, but never the determining factor.
At one time it was thought, on the contrary, that a precocious ossification of the cranial cavity would arrest the development of the brain; microcephaly was believed to be caused by a precocious closing of the sutures of the cranial bones; and there was a certain period when the surgical treatment of microcephaly consisted in the removal of a portion of the cranial bone, in order to allow the brain to develop freely.
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 obliterated until very late, and there are anomalous cases where it has remained throughout life, giving the forehead a characteristic form (pronounced frontal nodules and a slight palpable furrow along the medial line of the forehead).
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.