CRANIUM. — The bony head is made up of two distinct portions: the *cerebral cranium*, which contains the brain (v. BRAIN), and the *facial cranium*, which contains various sense organs and the organs of mastication. The cranium properly so called, or cerebral cranium, is essentially a bony box for the protection of the most important part of the central nervous axis. For this reason, its study has always aroused particular interest from various points of view—anatomical, physiological, anthropological, and clinical.
The bones that compose it are essentially eight: the frontal, the ethmoid, the sphenoid, the occipital, the two parietals, and the two temporals. Between these, however, there often intercalate supernumerary ossicles, more or less numerous and developed, known as Wormian bones. These bones are classifiable among the flat bones and consist of two laminae of compact tissue, an external and an internal one, enclosing between them a layer of spongy tissue, the thickness of which varies greatly and is called the diploë. The inner table (or lamina) is in contact with the brain and is moulded, like wax, over its irregularities. Hence the grooves of the inner table correspond, as in a negative, to the cerebral convolutions, while the projections (mammillary eminences) correspond to the cerebral sulci. Similarly, on the inner table, the negative impressions of the arteries and large venous channels running over the surface of the hemispheres are found. The study of cerebral morphology through such impressions is, however, subject to many reservations because of the uncertainty of the determinations.
The bones of the facial cranium are distinguishable into two groups: an upper (maxillary superior portion) and a lower (maxillary inferior portion). The lower portion consists of the mandibular box, while the upper portion consists of thirteen distinct bones: the maxilla, the malar (zygomatic) bone, the lacrimal (unguis), the inferior nasal concha, the nasal bone, and the palatine bone—all of which are paired and symmetrically arranged with respect to the median plane of the cranium—and the unpaired vomer. The human cranium is studied from a descriptive standpoint in anatomy, but its interest is still generally shared by anthropologists, who, through disparate comparisons, seek to define the differentiating characteristics of bones, race, sex, individual ages, etc.
Among the classical names of scholars in the history of anthropology most closely associated with craniological research, the following should be mentioned: C. M. Daubenton (1744), G. F. Blumenbach (1775), P. Camper (1791), G. Prichard (1807), and later Geoffroy Saint-Hilaire, F. Cuvier, A. Forville, G. B. Parchappe, G. Serra, P. P. Broca, and G. Sergi. But the list of researchers could be extended much further, for morphological and metric studies of bones have always constituted an essential chapter in anthropology (v. ANTHROPOLOGY). This may seem exaggerated, since the human organism is not revealed solely through its bones, but it is understandable for various reasons: practically speaking, comparative material is more easily obtained from bones, while in the case of fossil humans, bones are the only remains preserved. For this reason, anthropologists have had to face complex problems regarding the origins of human forms and their related transformations, which they have had to resolve through skeletal remains. Naturally, the cranium has been the object of the majority of these investigations, and in reality, it reveals the most reliable differentiating characteristics among the most disparate groups, along with traces of phylogenetic evolution over time.
Let us touch upon the most important findings for racial classification, which also serve as a basis for the study of fossils.
The morphology of individual bones is examined in relation to group or individual differentiations, but particular attention is given to the shape of the entire cerebral cranium, viewed according to specific standards, and of the facial cranium in its essential portions.
The shape of the cerebral cranium, viewed from above, vertically to its maximum contour, often serves as a good racial differentiator, albeit with reservations regarding the early attempts of Giuseppe Sergi, who was the brilliant initiator of this method. Around 1895, he distinguished the following cranial forms: 1) pentagonoid; 2) rhomboid; 3) ovoid; 4) beloid; 5) cuboid; 6) sphenoid; 7) sphaeroid; 8) platycephalic. Frassetto later reduced these to six, but always following the same methodological principle of observation. These forms nonetheless give an idea of the actual contour of the cranium (in the vertical norm) and morphologically supplement the results obtained from the study of the cephalic index introduced by A. Retzius (1842). This is the principal craniometric index used to date, expressed as the percentage ratio of the maximum width of the cranium to its length. Other indices are used which take height or other combinations of measurements into account, but racial differences are always more notable in the aforementioned norm of observation. Based on the cephalic (or cranial, as it is more properly called when determined from skeletal remains) index, the following classification of values (and thus of forms) is commonly used: dolichocephalic (long crania) with an index up to 74.9; mesocephalic (medium-length crania) with an index from 75 to 79.9; brachycephalic (short crania) with an index of 80 or above. But this classification is evidently only indicative in purpose. The boundaries between the above forms are arbitrary, and in practice, apart from hybridism and mixtures, no race is ever found to consist entirely of individuals belonging to a single index category. In nature, no discontinuity of this kind has been observed unless the analysis of the individual characteristics determining overall forms is pursued in much greater depth.
It should be noted, however, that modern studies, while not abandoning the diagnostic utility of cranial indices in general, seek to resolve classification problems without resorting to arbitrary subdivisions of the naturally occurring variability within individual groups. Instead, the study of this variability is being increasingly deepened, both through graphical representations and through appropriate statistical methods of data processing.
An example. If one plots the data on a Cartesian co-
CRANIUM — Examples of variation in facial prognathism in two African crania (schemes derived from figures by De Quatrefages and Hamy). A) Prognathous cranium, Congo Negro; B) Orthognathous cranium, Coptic. The orientation of the two subjects is based on the orbito-auricular plane of the German Convention.
On the abscissa, a scale of possible values of the cranial index is plotted, and on the ordinate, a scale of individual frequencies. By plotting the data of two human groups on this graph, broken lines are obtained which, if by an arithmetical device the group means are aligned on the same vertical and the areas of the graph remain equal in total extent, represent the real individual variability comparable within the categories or series under comparison. In the annexed figure, the broken line for the Romans shows the existence of a transvariation, i.e., a mixture of two different types within the same group, types which, taken individually, would present a monocuspid distribution. They correspond to *Homo mediterraneus* and *Homo alpinus* (v. RAZZE UMANE).
The broken line for the Melanesians also reveals a heterogeneity in the group, with the presence of dolichomorphic Melanesians (consisting of various cranial varieties according to G. Sergi) and brachymorphic Melanesians, who appear as a group secondarily mixed with the main dolichomorphic one.
In the same metric data of the cranium, the study of correlations is of particular value, as it has highlighted racial differences of considerable systematic significance while clarifying different behaviors of various cranial regions. Indeed, the correlation between the length and width of the cranium in individual groups (belonging to the most disparate races) has been examined, and certain positive values have been found which reveal that, as length increases, width also tends to increase on average from one individual to another. However, the same procedure applied to the racial means of multiple human groups yielded a null or even negative correlation. This means that the ratio between the two measurements varies far more among different races than among individuals of the same race. The importance of this result is evident when one considers that there are cranial diameters (e.g., of the facial skeleton) that behave in exactly the opposite manner: racial differences in these ratios are much smaller than individual ones, in other words, the interracial correlation is greater than the intraracial one. This is a completely opposite behavior among different measurements, which has only recently been demonstrated through biometric methods, contrary to the pessimistic predictions of various authors (v. SACCHETTI, FRANCO).
Among the other most commonly used cranial indices as indirect assessments of shape, the following should be noted: the vertico-longitudinal index (used to evaluate cranial height according to categories such as chamaecephalic, orthocephalic, and hypsicephalic), the fronto-parietal index, the total facial index (used to evaluate facial height according to categories such as euryprosopic, mesoprosopic, and leptoprosopic), the orbital index (used to evaluate orbital height according to categories such as chamaeconch, mesoconch, and hypsiconch), and the nasal index (used to evaluate nasal aperture width according to categories such as leptorrhine, mesorrhine, and platyrrhine). However, some indices, such as the total facial index, while generally used for racial differentiation, have today been shown to be entirely unsuitable for this purpose (using the aforementioned biometric methods) due to their high individual variability and thus their limited diagnostic value in the field of human systematics. In general, these metric assessments should always be supplemented with a detailed morphological analysis of individual skeletal regions, along with a study of their topographical position relative to the fundamental orientation planes of the cranium. The latter have particularly engaged the attention of anthropologists, e.g., in assessing the prognathism of fossil humans. Yet the best results have been obtained on physiological and morphomechanical premises.
In the same line of research, studies aimed at assessing cranial curves and angles (particularly at the base of the cranium, on the sphenoid, and the face) as well as cranial capacity have also been noteworthy. Observations on cranial capacity have yielded significant insights into corresponding inferences about brain mass, especially in the case of fossil humans (v. CERVELLO; ANTROPOLOGIA). The most important facial angle is the one used to assess prognathism, which has yielded good results for racial differentiation. It should be noted, however, that prognathism is now also determined analytically through the morphomechanical spatial study of individual bony elements. Particular attention should be drawn to this latter point. Modern craniology, in addition to establishing the systematic value in the differentiation of traits, aims to explain physiologically and mechanically the various architectural and structural adaptations of the skeleton. The function of mastication is evidently connected with the alveolar arch and the arrangement of individual bony elements, just as the architecture of the cranial vault depends on the spatial position of the temporal bone, which houses the organs of orientation. This dynamic correlation in craniogenesis has indeed been demonstrated in studies by G. Sergi on both modern and prehistoric humans.
Such analysis of the position and shape of individual bones in relation to the cranium as a whole and its physiological orientation planes is pursued using specific techniques and specially constructed apparatus (v. ANTROPOLOGIA). In the annexed figures, an example is given of a study of the isolated maxilla in relation to the fundamental planes, and the corresponding geometric diagrams, superimposed on one another, clearly show the differences sought, allowing for a more rational interpretation. It should be noted in this regard that the reference points for each bone are those that are architecturally most important in craniogenesis.
The annexed figures also provide notable examples of racial differences in various other characteristics of the human cranium.
There are also morphological and structural differences dependent on sex, which allow the male cranium to be distinguished from the female one even at the same age. The female cranium is generally said to retain a more infantile morphological complex, making it more delicate and slender than the male. It is also smaller, lighter, with less pronounced bony crests for muscle insertions, smaller mastoid processes, a more arched forehead (*forme bombée*) reminiscent of that in children, more developed frontal and parietal eminences, sharper superior orbital margins, a smaller overall cranial vault volume, etc. Naturally, all these typical traits serve in normal cases, but the anthropologist may encounter exceptions where diagnosis remains highly uncertain or even impossible. There are indeed cases in which female crania exhibit robustness traits entirely similar to those of males, to the point of being indistinguishable, while there are cases of male crania with delicate traits that are entirely confused with the corresponding traits of the other sex. The norm, however, is as indicated.
CRANIUM — Lateral norma of an Eskimo cranium with slight development of the glabellar region (from R. Martin). Lateral norma of an Australian cranium with strong development of the glabellar region (from Pöch).
The development of the cranium through the stages of life has likewise been studied so that the examination of various features allows for a reliable age diagnosis by the anthropologist. Particularly noteworthy are the transformations of the cranial vault in the child due to the ossification processes observed after birth within the so-called membranous cranium, which is formed by the fibrous tissue of the vault, while the cranial base soon becomes cartilaginous during the embryonic period (Kölliker’s basal plate). In the child’s membranous cranium (fontanelle period), numerous ossification centers are observed which gradually form the bones of the vault. Consequently, the angles of the cranial pieces, being farther from these original ossification centers, are the last to be filled with bony substance. Hence, the corresponding regions received the name of fontanelles. These are of interest to the obstetrician for prenatal diagnoses as well as to the anthropologist who observes the differing developmental behaviors across the most disparate races. With the disappearance of the fontanelles due to complete ossification of the vault, the margins of the individual bones assume a serrated shape that allows for a kind of reciprocal interlocking or inlay of contiguous elements. The complexity of these serrations in correspondence with the so-called sutures of the cranium varies from region to region but generally increases with age, though at different times in different racial groups. All these elements are valuable for diagnosing the age of individuals. The specialized anthropologist, however, can distinguish the not infrequent cases of anomalous suture obliteration as the final stage of synostosis. The residual membrane at the sutures is gradually invaded by bony tissue (as previously occurred at the fontanelles), so that the various parts of the cranium, even if at different times, eventually fuse completely. Naturally, one must also distinguish here a normal physiological process that leads to the classic cranium of old age, consisting of a single bony piece, from a pathological process that can even result in severe cranial deformities (microcephaly, scaphocephaly, plagiocephaly, etc.). It has also been debated whether a different progression in the obliteration of cranial sutures might explain the various cephalic forms according to, for example, G. Sergi’s schemes. But perhaps this is only one of the dynamic factors in craniogenesis, a factor that can nonetheless shed light when we seek to interpret the nature and proximate biological causes, at least for individual ethnic groups.
In conclusion, the human cranium varies with age, sex, and race in ways that are still the subject of study using modern methods of statistical and anthropological analysis. Very often, the most recent racial differences have not been explained in their nature, nor is their temporal evolution known. The so-called missing links between different forms are lacking.
The problems, however, are being increasingly explored, and research is progressively clarifying the behavioral patterns of individual traits across generations, as well as in cases of crossing or hybridization and under the influence of the most diverse environmental factors. The problem of racial mixtures is fundamental and often explains the genesis of new forms. Special missions involving different types have sometimes served as indirect evidence for observing the architectural adaptation of certain bony structures (the example in the figure, where two maxillary schemes of Arbore individuals are superimposed, has indeed been used in studies to explain the facial metamorphosis of those populations living on Lake Stefania at the boundary between the Negro and Hamitic inhabited worlds, where European facial forms prevail instead).
Finally, the problems of the plasticity of traits in relation to the environment have also been studied in the case of the cranium, especially regarding its general shape according to the cephalic index. Notable are the researches of F. Boas on immigrants in America, the data of Snigirew and Talko-Hrynewicz for Lithuania, of Fishberg for New York, of Elkind for Warsaw, of Zakrewsky, Majer, and Kopernicki for Galicia, of Hirsch for Massachusetts, of Guthe for Boston, as well as the investigations of Frets, Bryn, Schreiner, Geipel, Abel, Pessler, and the more recent ones of Dornfeldt and Sacchetti. The conclusions that seem most probable, according to the latter, suggest a reaction norm of individual traits (such as head shape) in the strict genetic sense of the expression, and in cases where transformations have been confirmed following environmental changes (due to the migration of entire groups, etc.). In particular, the cephalic index, in comparison with all other anthropometric traits of the bony head, has shown great and significant interracial variability; this result might seem to contradict the aforementioned knowledge about possible variations in the trait due to environmental stimuli. Yet a careful analysis of the phenomena shows that even those minor variations in head shape, which so concerned anthropologists at the beginning of the century (leading to a division into two opposing camps over whether to admit or exclude environmental influences), need not be seen as contradictory to the very capacity of the trait to differentiate groups, let alone to their actual differing morphological and demogenetic constitution when considering the strictly genetic and physiological aspect connected to II. This is a principle of reactivity tied to the individual genetic heritage and expressed through the phenotype. Thus, only in this way can we explain how, in the face of the same social and geographical environment (e.g., in the United States), racially different populations (Polish Jews, brachycephalic, and Sicilians, dolichocephalic Mediterraneans) have reacted in opposite ways to each other, regardless of their individual forms of mixture with local populations (Boas). Similar outcomes have been observed among some immigrant groups in Italy (Sacchetti). Environmental reactivity and heredity are thus not opposing concepts, at least for certain craniological traits in anthropology. But similar examples are already cited in various fields of genetics application, particularly demogenetics. Thus, alongside the static and exclusively morphological study of the human cranium, a new method of investigation has emerged in the field of demogenetic determinism, always in relation to the reciprocal mechanical adaptation of forms. This brings us ever closer to explaining the real, complex phenotypic expression of human groups as they are in their natural environment and their potential reactivity to external factors.
BML: List of particularly noteworthy publications to which the standard treatises on anatomy and physiology must be added. A. De Quatrefages - E. T. Hamy, *Crania ethnica. Les crânes des races humaines*, Paris 1882; P. Topinard, *Eléments d'anthropologie générale*, ibid. 1885; G. Sergi, *Specie e varietà umane*, Turin 1900; S. Jacob, A. Lee, K. Pearson, *Preliminary Note on the interracial characters and their correlation in Man*, in *Biometrika*, 2 (1902-1903); E. Auerbach, *Zur Plastizität des Schädels mit Bemerkungen über den Schädellinde*, in *Arch. f. Rassen u. Gesellschaftsbiologie*, 5 (1912); F. Boas, *Changes in bodily forms of descendants of immigrants*, Columbia Univ. Press, New York 1912; F. Boas-H. M. Boas, *The head-forms of the Italians as influenced by heredity and environment*, in *American Anthropologist*, new series, 15 (1913); W. Gregory, *The origin and evolution of the human dentition*, in *Journ. of dental Research*, 2 (1920) and 3 (1921); A. Ivanowsky, *Physical modifications of the populations of Russia under famine*, in *American Journ. of Physic. Anthropol.* 6 (1923); K. Pearson-L. H. C. Tippet, *On stability of the cephalic indices within the race*, in *Biometrika*, 16 (1924); A. Schreiner, *Zur Erblichkeit der Kopfform*, in *Genetica*, 5 (1924); K. Hilden, *Zur Kenntnis der menschlichen Kopfform in genetischer Hinsicht*, in *Hereditas*, 6 (1925); M. J. Herskovits, *Correlation of length and breadth of head in american negroes*, in *American Journ. of Phys. Anthropol.* 9 (1926); N. Hirsch, *Cephalic index of americanborn children of three foreign groups*, ibid., 10 (1927); S. Sergi-V. CAPRI, *Osservazioni sui rapporti di forma e dimensione tra le volte delle orbite ed il c. cerebrale*, in Riv. di antropol., 28 (1928-29); R. Martin, *Lehrbuch der Anthropologie*, Jena 1928; F. Frassetto, *Les formes normales du crâne humain*, in Bull. de la Soc. de Morph., 3-4 (1929); S. Sergi-J. Pastore, *Sulle variazioni di forma delle orbite negli Omididi*, in Riv. di antropol., 29 (1930); P. Godin, *Idé-rité de l'indice cefalique*, in Bull. et Mém. de la Soc. d'anthrop. de Paris, 8 (1931); G. P. Fretz, *Über die Dominanz des brachypothalamen Kopfindex*, in Zeitschrift. f. Morphol. u. Anthropol., 20 (1931); Saller, Gutbier, Kohl, Schiereck, *Über die Vererbung der Kopfmasse u. Indizes*, in Zeitschrift. f. Konstitutionelle, 18 (1933); W. Abel, *Die Vererbung von Antlitz und Kopfform des Menschen*, in Zeitschrift. f. Morph. u. Anthrop., 33 (1934); S. Sergi, *Sulle variazioni di forma e di posizione dell'osso temporale nell'uomo*, in Riv. di antropol., 31 (1935-36); G. Pessler, *Untersuchung über den Einfluss der Grossstadt auf die Kopfform*, in Zeitschrift. f. Morph. u. Anthrop., 38 (1936); S. Sergi, *Sulle variazioni di posizione dell'osso megalitico nell'uomo*, in Riv. di antropol., 33 (1940-42); W. Dornfeldt, *Studien über Schädelform und Schädelveränderung von Berliner Ostjuden und ihren Kindern*, in Zeitschrift. f. Morphol. u. Anthrop., 39 (1941); A. Sacchetti, *Variabilità e correlazione intra ed interrazziale*, in Atti Acc. d'Italia, 7° serie, 3 (1942); id., *Sul valore dell'indice facciale come mezzo di differenziazione dei gruppi umani*, in Atti IV Riun. Soc. Ital. di statistica, 1942; id., *Le variazioni intra ed interrazziali dell'indice cefalico*, in Riv. di antropol., 34 (1942-43); G. Natoli, *L'indice cefalico nei primi mesi di vita*, ibid.; A. Sacchetti, *Ricerche comparate sull'architettura facciale dei melanesiani*, in Riv. di biologia cefalico, 7 (1946); S. Sergi, *Il secondo Paleantropo di Saccolopastro*, in Riv. di antropol., 36 (1948); A. Sacchetti, *Il metamor-fismo razziale come fattore di adattamento morfologico ad architetturale della faccia umana*, in Archivio zoologico italiano, 34 (1949).
CRANIUM - Examples of extreme variations in the shape of the orbit (from Wolff). A) Egyptian cranium with hypsiconchy, B) Australian cranium with chamaeconchy.