Craniometry

Craniometry. The application of precise methods of measurement marks a definite phase in the development of most branches of modern science, and thus craniometry, a comprehensive expression for all methods of measuring the skull (cranium), provides a striking landmark in the progress of anthropological studies. The origin of craniometry appears to be twofold. Certain artists made measurements of heads and skulls with a view to attaining greater accuracy in their representation of those parts of the human frame. Bernard de Palissy and A. Dürer may be mentioned as pioneers in such researches. Again, it is clearly shown in the literature of this subject, that anatomists were led to employ methods of measurement in their study of the human skull. The determining cause of this improvement in method is curious, for it appeared at the end of a famous anatomical controversy of the later middle ages, namely the dispute as to whether the Galenic anatomy was based on the study of the human body or upon those of apes. In the description of the dissection of a chimpanzee (in 1680) Tyson explains that the measurements he made of the skull of that animal were devised with a view to exhibiting the difference between this and the human skull.

The artists did not carry their researches very far. The anatomists on the contrary continued to make measurements, and in 1764 Daubenton published a noteworthy contribution to craniometry. Six years later, Pieter Camper, distinguished both as an artist and as an anatomist, published some lectures containing an account of his craniometrical methods, and these may be fairly claimed as having laid the foundation of all subsequent work. That work has been described above as anthropological, but as the studies thus defined are very varied in extent, it is necessary to consider the subdivisions into which they naturally fall.

Fig. 1.—The Skull and head of a young orang-utan, and of a negro, showing the lines including the facial angle (MGND) devised by Pieter Camper.

In the first place (and omitting further reference to the contributions of artists), it has been explained that the measurements were first made with a view to elucidating the comparison of the skulls of men with those of other animals. This wide comparison constitutes the first subdivision of craniometric studies. And craniometric methods have rendered the results of comparison much more clear and comprehensible than was formerly the case. It is further remarkable that among the first measurements employed angular determinations occur, and indeed the name of Camper is chiefly perpetuated in anthropological literature by the “facial angle” invented by that artist-anatomist (fig. 1). It appears impossible to improve on the simple terms in which Camper describes the general results of the employment of this angle for comparative purposes, as will appear from the following brief extract from the translation of the original work: “The two extremities of the facial line are from 70 to 80 degrees from the negro to the Grecian antique: make it under 70, and you describe an ourang or an ape: lessen it still more, and you have the head of a dog. Increase the minimum, and you form a fowl, a snipe for example, the facial line of which is nearly parallel with the horizon.” (Camper’s Works, p. 42, translated by Cogan, 1821.)

In the 19th century the names of notable contributors to the literature of craniometry quickly increase in number; while it is impossible to analyse each contribution, or even record a complete list of the names of the authors, it must be added that for the purposes of far-reaching comparisons of the lower animals with mankind, craniometric methods were used by P. P. Broca in France and by T. H. Huxley (figs. 2 and 3) in England, with such genius and success as have not yet been surpassed.

The second division of craniometric studies includes those in which the skulls of the higher and lower races of mankind are compared. And in this domain, the advent of accurate numerical methods of recording observations brought about great advances. In describing the facial angle, it will be seen that the modern European, the Greek of classical antiquity and the Negro are compared. Thus it is that Camper’s name appears as that of a pioneer in this second main division of the subject. Broca and Huxley cultivated similar comparative racial fields of research, but to these names that of Anders Retzius of Stockholm must be added here. The chief claim of Retzius to distinction rests on the merits of his system of comparing various dimensions of the skull, and of a classification based on such comparisons. These indices will be further defined below. It is convenient to mention here that the first aim of all these investigators was to obtain from the skull reliable data having reference to the conformation or size of the brain once contained within it. Only in later days did the tendency to overlook this, the fundamental aim and end of craniometry, make its appearance; such nevertheless was the case, much to the detriment of craniometric science, which for a time seems to have become purely empirical.

Fig. 2.—The spheno-ethmoidal, spheno-maxillary and foramino-basal angles are shown in the crania of:—A, a New Britain native (male); B, a gorilla (male) C, a dog. N.Pr.B, Spheno- ethmoidal angle; P.Pr.B, Spheno-maxillary angle; Pr.B.Op, Foramino-basal angle. The spheno- ethmoidal and spheno-maxillary angles were first employed by Huxley.

Fig. 3.—The spheno-ethmoidal, spheno-maxillary and foramino-basal angles are shown in the crania of:—A, a New Guinea native (male); B, a European woman. N.Pr.B, Spheno-ethmoidal angle; P.Pr.B, Spheno-maxillary angle; Pr.B.Op, Foramina-basal angle.

The third subdivision of craniometric researches is one in which the field of comparison is still further narrowed. For herein the various sub-racial types such as the dark and fair Europeans are brought together for the purposes of comparison or contrast. But although the range of research is thus narrowed and restricted, the guiding principles and the methods remain unchanged. In this department of craniometry, Anders Retzius has gained the foremost place among the pioneers of research. Retzius’s name is, as already mentioned, associated not with any particular angle or angular measurement, but rather with a method of expressing as a formula two cranial dimensions which have been measured and which are to be compared. Thus for instance one skull may be so proportioned that its greatest width measures 75% of its greatest length (i.e. its width is to its length as three to four).

From Tylor's Anthropology, by permission of Macmillan & Co., Ltd.

Fig. 4.—Top view of skulls. (A) Negro, index 70, dolichocephalic; (B) European, index 80, mesaticephalic; (C) Samoyed, index 85, brachycephalic.

This ratio (of 75%) is termed the cephalic or breadth-index, which in such an instance would be described as equal to 75. A skull providing a breadth-index of 75 will naturally possess very different proportions from another which provides a corresponding index equal to 85. And in fact this particular index in human skulls varies from about 58 to 90 in undistorted examples (fig. 4). Such is the general scheme of Retzius’s system of classification of skulls by means of indices, and one of his earliest applications of the method was to the inhabitants of Sweden. One striking result was to exhibit a most marked contrast in respect of the breadth-index of the skull, between the Lapps and their Scandinavian neighbours, and thus a craniometric difference was added to the list of characters (such as stature, hair-colour and complexion) whereby these two types were already distinguished. Since the publication of Retzius’s studies, the cephalic or breadth-index of the skull has retained a premier position among its almost innumerable successors, though it is of historical interest to note that, while Retzius had undoubtedly devised the method of comparing “breadth-indices,” he always qualified the results of its use by reference to other data. These qualifications were overlooked by the immediate successors of Retzius, much to the disadvantage of craniometry. In addition to the researches on the skull forms of Lapps and Swedes, others dealing with the comparison of Finns and Swedes (by Retzius) as well as the investigation of the form of skull in Basques and Guanches (by Broca) possess historic interest.

Fig. 5.—Callipers used in Craniometry, Professor Martin’s (P. Hermann, Zürich) model.

Fig. 6.—Flower’s Craniometer as modified by Dr W. L. H. Duckworth.

Thus far little or nothing has been said with regard to instruments. Camper devised a four-sided open frame with cross-wires, through which skulls were viewed and by means of which accurate drawings could be projected on to paper. The methods of Retzius as here described require the aid of callipers of various sorts, and such instruments were quickly devised and applied to the special needs of the case. Such instruments are still in use, and two forms of simple craniometer are shown in the accompanying illustrations (figs. 5 and 6). For the more accurate comparison required in the study of various European types, delicate instruments for measuring angles were invented by Anthelme in Paris (1836) and John Grattan in Belfast (1853). These instruments enabled the observer to transmit to the plane surface of a sheet of drawing paper a correct tracing of the contour of the specimen under investigation. A further modification was devised by the talented Dr Busk in the year 1861, and since that date the number and forms of these instruments have been greatly multiplied. With reference to contributors to the advance of knowledge in this particular department of craniometry, there should be added to the foregoing names those of Huxley, Sir W. H. Flower and Sir W. Turner in England, J. L. A. de Quatrefages in France, J. C. G. Lucae and H. Welcker in Germany. Moreover, the methods have also been multiplied, so that in addition to angular and linear measurements, those of the capacity or cubical contents of the cranium and those of the curvature of its surface demand reference. The masterly work of Cleland claims special mention in this connexion. And finally while two dimensions are combined in the cephalic index of Retzius, the combination of three dimensions (in a formula called a modulus) distinguishes some recent work, although the employment of the modulus is actually a return to a system devised in 1859 by Karl E. von Baer.

Fig. 7.—The facial angle of the Frankfort Agreement is shown in the crania of:—A, a New Britain native (male) 62°; B, a gorilla (male) 50°; C, a dog 42°. This angle has now replaced the facial angle of Camper (cf. fig. 1).

The fourth subdivision of craniometry is closely allied to that which has just been described, and it deals with the comparison of the prehistoric and the recent types of mankind. The methods are exactly similar to those employed in the comparison of living races; but in some particular instances where the prehistoric individual is represented only by a comparatively minute portion of the skull, some special modifications of the usual procedures have been necessitated. In this field the works of W. His and L. Rütimeyer on the prehistoric races of Switzerland, those of Ecker (South Germany), of Broca in France, of Thurnam and Davis in England, must be cited. G. Schwalbe, Kramberger, W. J. Sollas and H. Klaatsch are the most recent contributors to this department of craniometry.

Fig. 8.—The facial angle of the Frankfort Agreement is shown in the crania of:—A, a Guinea native (male) 75°; B, a European (woman) 93°; C, a new-born infant (93°).

Thus the complexity of craniometric studies has inevitably increased. In the hands of von Török of Budapest, as in those of M. Benedikt of Vienna at an earlier date, the number of measurements regarded as necessary for the complete “diagnosis” of a skull has reached a colossal total. Of the trend and progress of craniometry at the present day, three particular developments are noteworthy. First come the attempts made at various times to co-ordinate the systems of measurements so as to ensure uniformity among all observers; of these attempts two, viz. that of the German anthropologists at Frankfort in 1882 (figs. 7 and 8), and that of the Anthropometric Committee of the British Association (1906) seem to require at least a record. In the second place, the application of the methods of statistical science in dealing with large numbers of craniometric data has been richly rewarded in Prof. Karl Pearson’s hands. Thirdly, and in connexion with such methods, there may be mentioned the extension of these systems of measurement, and of the methods of dealing with them on statistical principles, to the study of large numbers of the skulls of domestic and feral animals, such as white rats or the varieties of the horse. And lastly no account of craniometry would be complete without mention of the revolt, headed by the Italian anthropologist Sergi, against metrical methods of all kinds. It cannot, however, be alleged that the substitutes offered by the adherents of Sergi’s principles encourage others to forsake the more orthodox numerical methods.

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