AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 88:323-345 (1992)

Effects of Fronto-Occipital Artificial Cranial Vault Modification on the Cranial Base and Face JAMES M. CHEVERUD, LUCI A.P. KOHN, LYLE W. KONIGSBERG, AND STEVEN R. LEIGH Department of Anatomy & Neurobiology, Washington University School of Medicine, St. Louis, Missouri 63110 (J.M.C.,LA.P.K.);Department of Anthropology, University of Tennessee, Knoxville, Tennessee 37916 (L.W.K.);Department of Anthropology, Northwestern Unzuersity, Euanston, Illinois 60201 (S.R.L.)

KEY WORDS Artificial deformation, Ancon, Songish, Finite element scaling, Cranial growth

ABSTRACT Artificial reshaping of the cranial vault has been practiced by many human groups and provides a natural experiment in which the relationships of neurocranial, cranial base, and facial growth can be investigated. We test the hypothesis that fronto-occipital artificial reshaping of the neurocranial vault results in specific changes in the cranial base and face. Fronto-occipital reshaping results from the application of pads or a cradle board which constrains cranial vault growth, limiting growth between the frontal and occipital and allowing compensatory growth of the parietals in a mediolateral direction. Two skeletal series including both normal and artificially modified crania are analyzed, a prehistoric Peruvian Ancon sample (47 normal, 64 modified crania) and a Songish Indian sample from British Columbia (6 normal, 4 modified). Three-dimensional coordinates of 53 landmarks were measured with a diagraph and used to form 9 finite elements as a prelude to finite element scaling analysis. Finite element scaling was used to compare average normal and modified crania and the results were evaluated for statistical significance using a bootstrap test. Fronto-occipitally reshaped Ancon crania are significantly different from normal in the vault, cranial base, and face. The vault is compressed along an anterior-superior to posterior-inferior axis and expanded along a mediolateral axis in modified individuals. The cranial base is wider and shallower in the modified crania and the face is foreshortened and wider with the anterior orbital rim moving inferior and posterior towards the cranial base. The Songish crania display a different modification of the vault and face, indicating that important differences may exist in the morphological effects of frontooccipital reshaping from one group t o another. o 1992 Wiley-Liss, Inc. The cultural practice of artificially reshaping neurocranial vault form by various constraining appliances provides a “natural experiment” for investigating the relationship between cranial vault growth and growth of the cranial base and face in humans. Artificial reshaping of the neurocranium produces an increased range of variation in cranial vault form in a characteristic fashion. By increasing the range of morpho0 1992 WILEY-LISS, INC

logical variation in the neurocranial vault, normally subtle and difficult to detect relationships between neurocranial and facial growth can be discovered. While such effects

Received July 30, 1991;accepted January 9,1992. Address reprint requests to James M. Cheverud, Department of Anatomy & Neurobiology, Box 8108, Washington University School ofMedicine, 660 S. Euclid Ave., St. Louis, MO 63110.

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may not play a major role in organizing variation within a normal human population, they can be important in wider comparisons of populations over evolutionary time and in determining the underlying developmental bases of cranial variation within Homo sapiens and during hominid evolution. In this report we consider the effect of one form of artificial reshaping, fronto-occipital flattening, on growth of the cranial vault, base, and face. Fronto-occipital flattening results from binding the frontal to the occipital regions of the head using pads or boards. This binding constrains cranial vault growth primarily to a mediolateral dimension, restricting growth in anterior-posterior and superior-inferior dimensions, resulting in a short, wide cranial vault. The frontal and occipital lose their normal curvature and appear flattened. We analyze the morphology of the cranial base and face in order to determine whether direct modification of cranial vault shape results in indirect effects on the cranial base and face. We carried out this analysis in two different groups, the prehistoric Peruvian Ancon and the Northwest Coast Songish Indians. Each of these groups used different reshaping devices with varying effects on the cranial vault, although both are classed in the fronto-occipital flattening category. This type of deformation is also referred to as “Cowichan” (Boas, 1891), tabular erect (Imbelloni, 19251, “fronto-vertico occipital” (Neumann, 19421, and anterior-posterior (Anton, 1989) and was practiced by a number of Coast Salish groups living in British Columbia (Boas, 1891; Cybulski, 19751, by some coastal prehistoric Peruvian populations (Dorsey, 1895; Dingwall, 1931), and by Caddoan-speaking Indians from the southern United States (Bennett, 1961). Earlier studies of artificial cranial reshaping were descriptive and classificatory in nature (e.g., McGibbon, 1912; Dingwall, 19311, while later studies applied standard craniometric or cephalometric procedures in comparisons between reshaped and unmodified crania (Oetteking, 1924; Blackwood and Danby, 1955; Moss, 1958; Bjork and Bjork, 1964; McNeill and Newton, 1965; Hellmuth, 1970; Cybulski, 1975; Hanzel, 1977; Droessler, 1981; Shipman, 1982;

Heathcote, 1986; Anton, 1989). These studies have suggested effects of vault reshaping on the cranial base and face, but have not been consistent in their findings. Unlike the conspicuous modifications to the cranial vault, modifications of the cranial base are more subtle. Most workers find that the cranial base is wider in fronto-occipitally flattened crania (McNeill and Newton, 1965;Anton, 1989)and that the cranial base angle is more open (platybasic) in modified individuals (Oetteking, 1924; NcNeill and Newton, 1965; Hanzel, 1977; Anton, 1989). In contrast, Moss (1958) found that his “vertically deformed” group displayed a more closed cranial base, or clival kyphosis. In the most recent and carefully controlled study of artificial reshaping, Anton (1989) was unable to reproduce Moss’s (1958) results even though she correctly pointed out that Moss’s classification of crania was different than that used by other workers and accounted for this in her analysis. It is even more difficult to evaluate the effects of artificial vault reshaping on the face as reported in the literature. Bjork and Bjork (1964) provided some evidence for a shorter cranial base, maxilla, and mandible in fronto-occipitally reshaped crania. Cheverud and Midkiff (1992)found a wider intercondylar distance in mandibles from modified individuals in the Ancon series and suggested that there may also be an anterior-posterior shortening of the mandible. In the most complete study, Anton (1989) measured facial breadths and heights in Peruvian samples (including individuals from Ancon not included in the present study) and found that fronto-occipitally modified crania have wider faces (significantly wider for the biorbital, orbital, bimaxillary, and bizygomatic breadths) and higher faces (significantly larger upper facial height [nasion to prosthion]). Nasal height and width and palatal length and breadth were not different from normal in the modified group. Since cranial metric and non-metric traits appear to be dependent on common underlying developmental processes (Corruccini, 1976; Cheverud et al., 1979; Richtsmeier et al., 19841, it has been suggested that the frequency of skeletal non-metric traits of the vault, face, and cranial base are also affected

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by artificial vault reshaping. The most common finding has been an increase in lambdoidal wormian bones in artificially reshaped crania (Dorsey, 1897; Bennett, 1965; Ossenberg, 1970; Buikstra, 1976). El-Najjar and Dawson (1977) and Gottlieb (1978) did not detect this association in their samples. Konigsberg et al. (1992) found a general increase in sutural bones in artificially modified crania, including the Ancon series studied here. However, they were unable to detect any effects on facial non-metric traits. The results from non-metric traits confirm effects on the visibly reshaped cranial vault but do not provide convincing evidence of cranial base o r facial effects. Most of the studies cited above share a series of difficulties to a greater or lesser extent which impinge on the interpretation of cranial base and face modifications resulting from vault reshaping. A major problem has been in the selection of a control group to which the modified crania are compared. In many cases, the control group is quite clearly genetically distinct from the experimental group. As examples, Oetteking (1924) compared unmodified Chumash (Southern California) crania to reshaped Chinook (Northwest Coast and Lower Columbia River) crania. Moss (1958) compared modified crania from the Chinook, Peru, Bolivia, Louisiana, and the Dominican Republic to unmodified Kwakiutl (British Columbia) while McNeill and Newton (1965) compared fronto-occipitally reshaped and circumferentially modified crania from two different Northwest Coast tribes which are likely genetically distinct and practice different forms of cranial reshaping. Anton (1989) compared samples from geographically diverse areas of Peru, with the majority of the fronto-occipitally reshaped crania coming from the central coastal region while the unmodified controls are primarily from the southern coastal region. In each of these studies it is difficult to separate the effects of vault reshaping on the cranial base and face from the normal morphological variation expected among biologically diverse human groups. In an attempt to better control for the possibility of genetic and environmental differences between modified and unmodified groups, we will compare modi-

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fied and unmodified crania from single skeletal series. Another limiting factor in our interpretation of previous studies lies in their reliance on standard craniometric and cephalometric measurements of linear distances and angles between landmarks. These distances and angles often overlap different cranial regions making the precise location of morphological differences in these measurements problematic (Bjork and Bjork, 1964; McNeill and Newton, 1965; Hanzel, 1977). Furthermore, they are typically limited to dimensions which may not be the most different morphological dimensions among the groups compared (Cheverud and Richtsmeier, 1986). While such linear measurements and angles can certainly be informative, it is often difficult to detect local morphological variations using them (Moyers and Bookstein, 1979; Cheverud et al., 1983; Cheverud and Richtsmeier, 1986; Richtsmeier and Cheverud, 1986). We apply finite element scaling in the comparison among groups in an attempt to overcome these problems of mensuration and shed new light on the distinctions between normal and modified crania. MATERIALS AND METHODS Samples The samples in this study were chosen to allow the best possible control over the comparison between normal and modified crania. Two different samples of fronto-occipitally modified crania are included, Ancon and Songish, in order to determine whether this class of deformation is homogeneous and to determine the extent to which the results of this analysis can be generalized to other fronto-occipitally reshaped cranial samples. A further criterion was that both normal and modified crania should be available from the same skeletal series. Each series displays the full range of fronto-occipital flattening, from none to quite severe. We make this comparison within a single series as an attempt to control for subtle, genetically based, morphological differences between separate deforming and non-deforming populations which may confound our

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attempts to identify the effects of vault reshaping on facial growth. Peruvian Ancon The prehistoric Peruvian Ancon series was collected by George Dorsey (1895) in 1892 to be displayed at the World Columbian Exposition in Chicago and is currently housed at the Field Museum of Natural History. The sample was collected from the large “necropolis” at Ancon and probably dates to a number of different periods within the Middle Horizon (Huari Empire), lasting from approximately A.D. 600 to A.D. 1450 (Menzel, 1977). Dorsey (1895) noted that there was a custom of wearing bandages about the head which likely resulted in vault deformation, but did not believe that the deformation was intentional. Rather, he felt that it was an accidental side effect of the headdress. He also asserted that the crania displaying the greatest modification were those of greatest antiquity but since his excavations preceded any formal temporal schemes in Peruvian archeology, it is not clear how he determined which graves showed great antiquity. Ceramics associated with the Ancon crania should permit dating of individual graves but this work has not been done. The form of vault modification at Ancon is somewhat variable (Reichlen, 1982) but is generally of the fronto-occipital type. Occasionally, a depression can be found along the posterior portion of the sagittal suture, which may mark the position of a strap used in the deforming device (see Fig. 1) (Allison et al., 1981). The Ancon sample analyzed here contains 70 males and 41 females. The crania were visually scored for fronto-occipital flattening as not modified (27 male and 20 females), slightly modified (23 males and 10 females), and modified or greatly modified (20 males and 11 females) as described in Konigsberg et al. (1992). Modified skulls were identified by occipital flattening (the squamous occipital nearly orthogonal to the foramen magnum), extensive asymmetry, and frontal depressions. Extent of modification was a matter of judgment given the range of variation exhibited in the series.

Fig. 1. Two appliances which produce the fronto-occipital type of modification. A: Ancon headdress (modified from Allison et al., 1981).B: Songish cradle board (modified from Boas, 1891).

This classification scheme is highly repeatable (Konigsberg et al., 1992) and was confirmed by discriminant function analysis utilizing selected cranial vault arcs and chords. Two crania which were misclassified according to the discriminant function analysis and had high post-hoc probabilities of belonging to an alternative group were relocated to that group prior to analysis. Crania from both sexes and of varying degrees of modification were pooled for statistical analysis resulting in sample sizes of 47 unmodified and 64 modified crania. Results

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from separate analyses of the sexes and modification classes are similar to those reported here for the pooled analysis.

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tion within our sample, then the undeformed crania may serve as a relatively poor control. All but one of the modified crania are from Cox Island, British Columbia (the The Songish Indians remaining modified cranium is from VictoThe Songish Indian series is from a Coast ria). The provenience of this Cox Island is Salish group and was acquired in the vicin- uncertain as more than one island off the ity of Victoria, British Columbia, by Franz coast of British Columbia may have had this Boas. The Songish used an elaborate cradle- designation in historical time. Even so, Boas board with a pad across the front to com- certainly classified these crania as Songish press the infant’s head (see Fig. 1) (Boas, as did Cybulski (1975). The Songish sample is small, composed of 1891). The deformation was clearly intentional, for as Boas (1891, p. 572) notes, 6 unmodified and 4 modified male crania “They have a saying referring to children housed a t the Field Museum of Natural Hiswho have not been subjected to this treat- tory. Scoring was performed as above. Visument, and, therefore, according to Indian ally, the modified Songish crania are much taste, ill-looking” which translates as “as if more distinct than the Ancon. This small no mother had made you look nice.” Other sample is too small to detect subtle morphophysical manipulations to the face and rest logical effects but serves as a check on the of the body were performed at birth among results for the Ancon sample and allows us the Songish (Boas, 1891; Dingwall, 1931) to determine whether the Ancon results are but were of short duration and are thought applicable to other skeletal series containing fronto-occipitally reshaped cranial to have had no lasting effect. Given the cultural importance of vault vaults. modification in the Songish, a question may Measurements be raised concerning the origin of the unmodified crania from this series. All of the The three-dimensional coordinates of 53 unmodified crania utilized in this study are landmarks were collected using a diagraph from the Victoria, British Columbia, region (See Table 1)and input t o the computer with and there was an Indian reservation (the a two-dimensional digitizing tablet, the Songhees Reservation) near Victoria. Indi- third dimension being entered directly. The viduals who grew up on or near the reserva- crania were then registered using the antetion may have remained unmodified because rior nasal spine as the origin. The X axis modification was probably discouraged by extends from anterior t o posterior between the British. It is also possible that the un- the anterior nasal spine and lambda. The Y modified crania are from a socially distinct axis is orthogonal to the X and runs mediogroup. Hill-Tout (1907, p. 40) reports that laterally, closely paralleling a line connect“There appear to have been recognized de- ing the right and left external auditory grees of contortion marking the social status meati. A superior-inferior Z axis is orthogoof the individual. For example, slaves, of nal to the other two. Group means were obwhich the Salish kept considerable num- tained by averaging coordinate values after bers, were prohibited from deforming the registration. heads of their children, consequently a norThese landmark coordinates were used as mal, undeformed, head was a sign and the basis of a finite element scaling analysis badge of servitude. And in the case of the (Lewis et al., 1980; Cheverud et al., 1983; base-born of the tribes the heads of their Cheverud and Richtsmeier, 1986; Richtschildren were customarily but slightly de- meier and Cheverud, 1986; Lozanoff and formed, while the heads of the children born Diewert, 1986; Moss, 1988; Moss et al., of wealthy or noble persons, and particu- 1985; Skalak et al., 1982; Bookstein, 1978, larly those of chiefs, were severely and ex- 1983,1984,1986,1987)of morphological difcessively deformed.” If Hill-Tout’s interpre- ferences between normal and modified cratation is correct and modification does nia. This analysis was carried out using represent an inherited social class distinc- the SCAL3D (Cheverud et al., 1983) and

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J.M. CHEVERUD ET AL TABLE 1. Landmarks recorded for Ancon a n d Songish crania a nd the composition of finite elements composed o f these landmarks Landmark 1. Intradentale superior 2. Premaxilla (R) [anterior alveolar ridge between the canine and premolar] 3. Premaxilla (L) 4. Posterior nasal spine 5. Nasale 6. Zygomaxillare superior (R) 7. Zygomaxillare superior (L) 8. Zygomaxillare inferior (R) 9. Zygomaxillare inferior (L) 10. Infratemporal crest (R) 11. Infratemporal crest (L) 12. Vomer spine 13. Nasion 14. Frontomalare (R) 15. Frontomalare (L) 16. Pterion (R) 17. Pterion (L) 18. Optic foramen (R) 19. Optic foramen (L) 20. Bregma 21. Bregma-nasion [point halfway along bregma-nasion arcl 22. Bregma-pterion (R) [point halfway along bregma-pterion arcl 23. Bregma-pterion (L) 24. Lambda 25. Asterion (R) 26. Asterion (L) 27. Bregma-lambda [point halfway along bregma-lambda arcl 28. Bregma-asterion (R) [point halfway along- bregma-asterion arcl 29. B r e h a -ast eri on (L) 30. Pterion-asterion (R) [point halfway along pterion-asterion arcl 31. Pterion-asterion (L) 32. Pterion-lambda (R) [point halfway along pterion-lambda arcl 33. Pterion-lambda (L) 34. Lambda-asterion (R) [point halfway along lambda-asterion arcl 35. Lambda-asterion (L) 36. Opisthion 37. Basion 38. Opisthion-lambda [point halfway along opisthion-lambda arcl 39. External auditory meatus (R) 40. External auditory meatus (L) 41. Temporo-sphenoid (R) 42. Temporo-sphenoid (L) 43. Jugular process (R) 44. Jugular process (L) 45. Foramen lacerum (R) 46. Foramen lacerum (L) 47. Anterior nasal spine 48. Posterior maxilla (R) 49. Posterior maxilla (L) 50. Zygomatic arch (R) 51. Zygomatic arch (L) 52. Optic foramen midpoint [average of 18 and 191 53. Pterion-asterion midpoint [average of 30 and 311 1, 2, 48, 4, 5, 6, 10, 12 Lower face (R) 1, 3, 49, 4, 5, 7, 11, 12 Lower face (L) 13, 14, 16, 52, 5, 6, 10, 12 Upper face (R) 13, 15, 17, 52, 5, 7, 11, 12 Upper face (L) 16, 30, 31, 17, 45, 43, 44, 46 Cranial base 24, 28, 30, 53, 25, 36, 38, 43 Posterior vault (R) 24, 29, 31, 53, 26, 36, 38, 44 Posterior vault (L) 20, 22, 27, 28, 16, 24, 25, 53 Anterior vault (R) 20, 23, 27, 29, 17, 24, 26, 53 Anterior vault (L)

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FIESCA (Morris, 1989) programs. Finite element scaling analysis measures the difference between forms and has the ability to localize morphological differences between individuals or populations to the regions surrounding specific anatomical landmarks. The registration described above is convenient for checking data, deriving means, and discussing the results but has no influence on the interpretation of the finite element scaling analysis. To carry out the finite element scaling analysis, three-dimensional coordinates are collected for a series of homologous landmarks (53 in this case). These landmarks are then connected to form a series of discrete, finite elements. Here, we formed 9 elements representing the right and left upper face, lower face, anterior cranial vault, and posterior cranial vault and the cranial base (see Fig. 2 and Table 1). These elements define a model of the skull and the analysis proceeds by measuring the amount of morphometric strain required to produce one model, the target, from the other, the reference. By morphometric strain we refer t o differences in morphometric size and shape between the objects being scaled, not to physical strain induced in bones during growth. The numerical outcome of a three-dimensional finite element scaling analysis at each landmark comparing a reference to a target object is a 3 x 3 symmetrical matrix called the form tensor (see Fig. 3) (Cheverud and Richtsmeier, 1986). This tensor measures the change in size and shape of a tetrahedron formed by the landmark of interest with the other three landmarks with which it is connected in the finite element. Thus it represents the change in position of a given landmark relative to the other three. For example, the results reported for the right premaxillary landmark refer to the tetrahedron formed by it with intradentale superior, the right maxillary tuberosity, and the right zygomaxillare superior landmarks within the right lower facial finite element (see Table 1and Fig. 2 ) . The form tensor measures the local strain a t each landmark required to reproduce the target form from the reference form. The tensor associated with each landmark de-

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scribes numerically the local change in size and shape from a sphere into an ellipsoid required in the transformation of the reference to target form (see Fig. 3). The diagonal elements of this matrix represent the increase or decrease in magnitude along the arbitrary X, Y, and Z axes of the reference form (normal strain) while the off-diagonal elements represent the change in angle between the X, Y, and Z axes in the reference form (shear strain) at any given landmark. The form tensor can be rotated to any arbitrary coordinate system and the local increase or decrease in length obtained for any arbitrary anatomical dimension. A particularly useful arbitrary coordinate system in which to consider the tensor is its principal coordinate system, the coordinate system in which all of the strain is normal and none is shear. The principal axes are the form tensor’s eigenvectors and remain orthogonal in both the reference and the target form. The principal values are the eigenvalues of the form tensor and measure the increase or decrease in size along their associated principal axes (see Fig. 3). The principal axes and values are analogous to the principal components and associated variances obtained in principal components analysis of a variancelcovariance matrix. The numerical results of a finite element scaling comparison between two forms can be displayed graphically by drawing the tensors as ellipses (or ellipsoids in three dimensions) on the reference form. One ellipse is drawn on each landmark displaying the localized morphological differences between the forms compared. The FIESCA program (Morris, 1989) draws these figures in twodimensional projections using the results of the scaling analysis. We have found true three-dimensional views to be difficult to view. It is conventional to first draw a circle around the landmark to represent the reference size and shape. The ellipse representing the form tensor (or deviation of the target from the reference form) is then superimposed on the landmark and the reference circle. Dimensions along which the target form is locally larger than the reference are indicated by radii of the ellipse which extend beyond the circle while dimensions along which the target form is locally

J.M. CHEVERUD ET AL.

330 A

Fig. 2. Landmarks listed in Table 1 are identified by number. The nine elements represent the right and left lower face, anterior cranial vault, and posterior cranial vault and cranial base and are illustrated by connecting the appropriate landmarks. Landmarks not connected by lines are not used in these analyses. A. View of cranium from the bottom. B: Lateral view of the cranium. Note that only landmarks and elements on the left side

of the cranium are represented in the lateral view, since their complements on the right side would appear superimposed in the figure. Superimposition occurred with lateral and midline landmarks 43 and 44,45and 46,30, 31, and 53, and 16 and 17, since the cranial base element shown in lateral view includes landmarks from both the right and left sides.

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ARTIFICIAL CRANIAL RESHAPING FORM

=

ASIZE

+

Li = In [(I + 2Pi)1/2]

ASHAPE

PI

where Piis the principal value and Li is the value transformed to a linear scale (Lozanoff and Diewert, 1986). The term within brackets [I (or the antilog of Li) is the proportional increase in length along the anatomical dimension specified. Local size change is the average of the linearized principal values

ASIZE ONLY

ap2

s = (L,

+ L, + L,)/3

while the amount of local shape change is their standard deviation t

ASHAPE ONLY

Fig. 3. Form strain tensor can be represented geometrically by an ellipse. The ellipse represents the local change in size and shape of a region surrounding a landmark in the comparison of a reference and a target form. The tensor describes the degree to which the circle changes size (increase or decrease) and is deformed into a n ellipse in the transformation. P1 and P2 represent the principal axes of deformation. The first figure illustrates form change as the sum of size change (increase) and shape change. The second figure represents a transformation involving only size change, with all anatomical dimensions increasing by the same amount. The third figure represents a transformation involving only shape change, there being no change in area while some anatomical dimensions increase and others decrease.

smaller than the reference form are indicated by ellipse radii which do not reach the circle’s boundary. A simple example of this type of finite element representation is presented in Figure 4. Two particularly useful measurements can be obtained from the principal values of the form tensor after transformation to a linear scale, local size change (s), and the amount of local shape change (t)(Cheverud and Richtsmeier, 1986). Transformation of the form tensor’s principal values or normal strains t o a linear scale is accomplished by the following equation:

=

{[(L, - Sl2 + (L,

-

Sl2

+ (L, - s)21/3}1”

(Cheverud and Richtsmeier, 1986).Thus, local size change measures the increase in size averaged over all anatomical dimensions while the amount of local shape change measures the differences in size change among anatomical dimensions. Bookstein (1984) developed statistical tests for similar size and shape metrics based on the multiplicative scale. The orientation of the local shape change is given by the principal axes of the form tensor. Global measures of size and shape differences were also obtained. Global size measures the difference in size over the whole skull by averaging local size measures across all landmarks. Global shape difference is measured by the standard deviation of local size measures across the landmarks (Cheverud and Richtsmeier, 1986). In addition we provide measures of percent volume change for each of the finite elements defined above. Statistics

Given the difficulties in deriving appropriate analytical statistical tests for landmark data (Bookstein, 1984, 1986; Lele and Richtsmeier, 19901, statistical tests will follow the nonparameteric bootstrap procedures suggested by Lele and Richtsmeier (1991). The observed difference between normal and reshaped skulls was obtained by measuring the strain required to deform the average normal skull into the average modified skull. For the Ancon, weighted averages were used to make the sex ratio of the nor-

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Fig. 4. Graphical representation of the morphological differences between two arbitrary forms. At each reference landmark, the circle represents no change, and the ellipse represents the magnitudes of increase or decrease in each anatomical direction between the reference and target forms. Dimensions along which the tar-

get is larger than the reference extend beyond the circle and dimensions along which the target is smaller than the reference do not extend beyond the circle. Form change at landmark 2 is characterized by a decrease in both the X and Y dimensions, but an increase in the +XY to -XY direction.

ma1 group correspond to that found in the modified group. Bootstrap normal and modified samples were obtained by random sampling with replacement from the complete unmodified sample. In the Ancon, this sampling was stratified by sex so that the sex ratio of the bootstrap normal and modified groups matched the sex ratio observed among the modified crania. The statistical significance of this difference was obtained as the proportion of bootstrap samples out of 500 for which differences exceeded those observed between the groups. The bootstrap procedure was also used to obtain statistical significance for local and global size and shape differences and element volumes. The particular pattern of local shape difference represented by the principal directions should be interpreted with caution unless the amount of local shape difference between the groups is statistically significant (Bookstein, 1984). The same warning holds concerning global shape difference.

RESULTS

Ancon

The average modified and unmodified Ancon crania are superimposed in lateral and basal views in Figure 5, after registration using Procrustes rotations (Goodall and Bose, 1987). From these figures it is apparent that the cranial vault is wider mediolaterally and foreshortened along an anterior-superior to posterior-inferior axis, confirming earlier visual impressions. The results of the finite element scaling analysis are given in Table 2 and Figure 6. Overall, there is no significant difference between normal and reshaped groups in overall cranial size or in the size of any of the 9 regions (elements) of the skull. The significant local size differences include a 4% reduction at lambda-opisthion. Other midline landmarks, bregma and opisthion, approach significant levels of reduction. All three landmarks lie under the deforming appliance (Allison et al., 1981).A 3%reduction of

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333

IL

Fig. 5. Superimposition of average normal (solid line) and average modified Ancon (broken line) after Procrustes registration of all landmarks. A Basal view. B: Lateral view.

the left lateral lower face (left premaxillary point and zygomaxillare superior) and the right lateral upper face (fronto-malare) was observed. There was a 2% increase in local size at the right bregma-asterion. However, the degree of variation in local size differences across the skull is not unusually large

and did not reach statistical significance (P = 0.122) so that these local size differences should be considered with caution. Local shape differences are common in the cranial vault, as expected given the direct application of deforming devices. Only right and left bregma-pterion, left pterion-aster-

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TABLE 2. Results of finite elements scaling analysis of normal into reshaped Ancon crania Landmark Cranial vault Bregma Bregma-lambda Lambda Lambda-opisthion Opisthion Pterion-aster. midpoint Pterion (R) Pterion (L) Bregma-pterion (R) Bregma-pterion (L) Bregma-asterion (R) Bregma-asterion (L) Pterion-asterion (R) Pterion-asterion (L) Asterion (R) Asterion (L) Cranial base Jugular process (R) Jugular process (Lj Foramen lacerum (R) Foramen lacerum (L) Optic foramen midpoint Vomer spine Infratemporal crest (R) Infratemporal crest (Lj Face Fronto-malare fR) Fronto-malare (L) Zygomaxillare sup. (R) Zygomaxillare sup. (L) Nasion Nasale Intradentale superior Posterior nasal spine Maxillary tuberosity (R) Maxillary tuberosity (L) Premaxilla-maxilla (R) Premaxilla-maxilla (L) Global Elements Lower face (R) Lower face (Lj Upper face (Rj Upper face (L) Cranial base Posterior vault (R) Posterior vault (L) Anterior vault (R) Anterior vault (L)

Size (Prob)

Shape (Prob)

PV1 (Dirj

PV2 (Dir)

-1.63 (0.96413 -1.80 (0.880) -0.77 (0.856) -3.76 (0.998)2 -1.32 (0.972)3 0.13 (0.352) 0.48 (0.222) 0.18 (0.556) 2.20 (0.030)3 0.29 (0.580) 1.87 (0.024)' 0.70 (0.198) 2.45 (0.066) -0.79 (0.742) 0.53 (0.224) 0.04 (0.460)

4.03 (0.001)' 5.52 (0.002)2 3.83 (0.001)* 6.22 (0.001)2 3.00 (0.002)2 3.51 (0.001)2 2.35 (0.002)2 2.65 (0.001)2 2.35 (0.310) 3.12 (0.140) 4.52 (0.006)' 3.99 (0.042)' 6.49 (0.036)2 4.20 (0.096j3 3.39 (0.001)' 2.02 (0.192)

2.6 (M-L) 6.0 (M-L) 3.5 (M-L) 1.4 (M-L) 0.9 (M-L) 4.5 (M-L) 3.8 (M-L) 3.6 (M-L) 5.5 (ALS-PMI) 4.2 (M-L) 8.3 (AM-PL) 6.5 (M-L) 10.6 (AL-PM) 4.9 (M-L) 3.6 (AMI-PLSj 2.5 (M-L)

0.4 (AI-PS) -3.9 (S-I) 0.1 (AI-PS) -0.1 (AI-PS) 0.7 (AI-PS) 0.4 (AI-PS) -0.2 (S-I) -1.3 (AI-PS) 1.8 (AMI-PLS) -1.8 (A-P) 1.3 (AL-PM) -0.5 (AI-PSI 4.1 (AMI-PLS) -1.5 (AMS-PLI) 2.4 (ALI-PMS) 0.2 (AI-PS)

-1.86 (0.972)3 -0.94 (0.846) 1.13 (0.322) 1.53 (0.228) 1.19 (0.078) 0.88 (0.172) -0.37 (0.616) 0.26 (0.364)

4.34 (0.02412 2.99 (0.098)3 4.33 (0.580) 2.62 (0.862) 2.81 (0.05413 2.81 (0.022)' 3.50 (0.09213 4.54 (0.000)2

2.5 (ALS-PMI) 2.5 (ALS-PMI) 7.1 (ALS-PMI) 5.7 (AL-PM) 4.3 (M-L) 3.8 (M-Lj 3.9 (M-L) 6.8 (M-L)

-0.2 (A-P) -0.5 (A-P) 0.8 (AMS-PLI) 0.0 (MI-LS) 2.1 (AI-PSI 1.2 (AI-PS) 0.0 (S-I) -1.1 (AI-PS)

-7.2 -4.6 -3.8 -0.8 -2.5 -2.2

-2.40 (0.974P -1.73 (0.896) -0.90 (0.706) -3.12 (0.984)' -0.96 (0.836) -0.76 (0.774) -1.06 (0.800) 1.84 (0.256) 0.15 (0.4121 0.06 (0.490) -0.57 (0.686) -2.96 (0.992)' -0.36 (0.732) Volume difference -0.20 (0.474) -2.96 (0.860) 0.37 (0.380) -1.45 (0.706) 2.56 (0.114) -2.15 (0.860) -2.37 (0.870) 0.86 (0.288) -0.53 (0.578)

5.29 (0.014)2 4.52 (0.184) 3.92 (0.100)3 4.69 (0.022)' 1.54 (0.480) 1.39 (0.196) 1.93 (0.07213 4.06 (0.402) 4.29 (0.024)' 3.84 (0.022)' 2.87 (0.168) 2.26 (0.284) 0.02 (0.122)

2.7 (MS-LI) 1.9 (AMI-PLS) 4.1 (MS-LI) 0.7 (AI-PSI 0.9 (M-L) 1.0 (M-L) 0.6 (S-I) 6.5 (S-I) 5.4 (M-L) 3.3 (M-L) 3.1 (M-L) -0.9 (AMS-PLI)

-0.1 (AMI-PLS) 1.1(AMS-PLI) -1.0 (AMI-PLS) -0.4 (AM-PL) -0.9 (A-P) -0.9 (S-I) 0.1 (M-L) 3.2 (M-L) 0.7 (ALS-PMIj 2.1 (S-I) -0.8 (A-P) -1.8 (AMI-PLS)

-8.8 (ALS-PMI) -7.5 (ALS-PMI) -5.3 (ALS-PMI) -8.8 (ALS-PMI) -2.8 (S-I) -2.3 (A-P) -3.6 (A-P) -3.5 (A-P) -5.1 (AI-PS) -5.2 (A-P) -3.8 (S-I) -5.8 (ALI-PMS)

PV3 (Dir)

~

-6.6 (AS-PI) -6.6 (A-P) -5.5 (As-PI) -11.1 (AS-PI) -5.3 (As-PI) -4.1 (As-PI) -2.0 (A-P) -2.6 (AS-PI) -0.5 (MS-LI) -3.0 (S-1) -3 2 (As-PI) -3.4 (As-PI) -5.8 (S-I) -5.2 (AS-PI) -4.1 (AS-PI) -2.5 (AS-PI)

(MS-LJ) (MS-LI) (AS-PI) (AMS-PLI) (AS-PI) (AS-PI) -4.6 (A-Pj -4.3 (AS-PI)

~~

~

I Measurementsreported include size and the proportion of bootstrap samples displaying a larger difference than that observed (a two-tailed test

so that landmarks with proportions greater than 97.5%are significantly smaller than normal while those with a proportion less than 2.5%are significantly larger); shape and the proportion of bootstrap sample showing larger shape differences than those observed (one-tailed test); the three principal values (PVi)and their associated anatomical dimensions(A, anterior; P, posterior;M, medial;L, lateral; S, superior;I, inferior).At the end of the table the proportionaldifferences in volume is given for each finite element. Indicates statistically significant at the 5% level. Indicates statistically significant at the 10%level.

ion, and left asterion failed to reach statistical significance for local shape change. As shown in Figure 6 and Table 2, the landmarks of the cranial vault are characterized by a mediolateral principal axis displaying about a 5%increase in the reshaped sample.

Even landmarks which do not have a strictly mediolateral principal axis have two principal axes associated with relatively large positive principal values running in a general mediolateral direction (right bregma-pterion, asterion, bregma-asterion, pterion-aste-

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A

B

z

I

Fig. 6. Finite element scaling results of the deformation of normal and modified Ancon drawn on the average normal Ancon cranium. Ellipses represent magnitudes and directions of difference between the normal and modified Ancon. Ellipses are exaggerated by a factor of 3 to aid in interpretation. A Basal view. B: Lateral view.

rion). The right pterion-asterion landmark displayed marked difference from the rest of the vault with a 10.6% increase along an anterior-lateral to posterior-medial dimension.

There is also an approximately 5% decrease in size along a principal axis running from anterior-superior to posterior-inferior throughout the cranial vault. This axis is approximately parallel to an axis joining

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bregma and lambda in a normal skull. The most extreme difference was a 11%decrease at lambda-opisthion. Overall the cranial vault is wider and compressed along an anterior-superior to posterior-inferior axis in the reshaped crania. There are only minor differences along an anterior-inferior to posterior-superior axis which remains relatively unaffected by the vault reshaping. In the cranial base, there was significant shape change at the vomer spine, the right jugular process, and the left infratemporal crest. Shape change at the left jugular process, the optic foramen midpoint, and the right infratemporal crest approached statistical significance. In the posterior portion of the cranial base, the jugular process decreased 6% along a lateral-inferior to medial-superior dimension and increased 2.5% along a lateral-superior to medial-inferior dimension indicating a shallower posterior cranial base. This is in contrast to the changes in the cranial vault and to non-significant changes at foramen lacerum which increased along an anterior-lateral to posterior-medial dimension by 6-7% on both sides. The anterior cranial base, with landmarks connecting the cranial base and face, displayed mediolateral increases of about 6 5 % at all landmarks, including the optic foramen midpoint, vomer spine, and the right and left infratemporal crests. These landmarks also displayed a slight 2 4 % decrease along an anterior-superior to posterior-inferior dimension. Decreases along this dimension are much smaller than for the same dimension in the cranial vault. Significant shape changes in the face were found at the right frontomalare, the right and left maxillary tuberosity, and the left zygomaxillare superior. The right zygomaxillare superior and intradentale superior both approached statistical significance. In the upper lateral face there is a relatively large decrease of about 7% along an anterior-lateral-superior to posterior-medial-inferior axis, paralleling a line connecting the right fronto-malare to the vomer spine. The alveolus shows a mediolateral increase at the maxillary tuberosities of about 5% accompanied by a generally anteriorposterior decrease of 5%. All facial points

display either a decrease or no change along the anterior-posterior axis. Note that there is little or no difference between groups along an anterior-medial-inferior to posterior-lateral-superior axis through the face. Songish The average modified and unmodified Songish crania are shown in lateral and basal views in Figure 7, after registration using Procrustes rotations (Goodall and Bose, 1987). From this figure it is apparent that the cranial vault is wider mediolaterally and foreshortened along an anterior-superior to posterior-inferior axis, as in the Ancon. It is also apparent that the asymmetry often seen in individual crania is more prominent in the means of this small sample than it was in the Ancon. The unmodified Songish crania were 12% larger in total volume than the reshaped crania. Since we are primarily interested in shape changes due to the deforming appliances, the reshaped crania were scaled up by multiplying all coordinate values by the cube root of 1.12. The results of the finite element scaling analysis are given in Table 3 and Figure 8. After resizing the modified crania, there is no significant difference between normal and reshaped groups in cranial size or in the size of any of the 9 regions (elements) of the skull, although the lower face seems to be smaller and the upper face larger in the modified crania. The only significant local size differences are a relative increase of 5% in anterior upper facial dimensions, an increase of 3.7% at the left bregma-asterion, and a decrease of 2.9% at lambda in the reshaped crania, There are several significant shape differences in the posterior and inferior cranial vault, including pterion, lambda, opisthion, pterion-asterion midpoint, right asterion, right bregma-asterion, and pterion-asterion. The midline points (bregma, bregmalambda, lambda, lambda-opisthion,opisthion, pterion-asterion midpoint) have an approximately 8.5%mediolateral increase and a 7% decrease along an anterior-superior to posterior-inferior axis. In contrast to these midline landmarks, anterior-lateral cranial vault landmarks, bregma-pterion and pterion, show an opposite morphological change,

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A

Y

L x

Fig. 7. Superimposition of average normal (solid line) and average modified Songish males (broken line) after Procrustes registration of all landmarks. The average of the modified Songish males was increased in overall size to equal the size of the average normal Songish male. A: Basal view. B: Lateral view.

with an approximately 9% increase along an anterior-medial-superior t o posterior-lateral-inferior dimension and a 7% decrease along an anterior-inferior to posterior-superior dimension. Posterior-lateral cranial

landmarks, (asterion, bregma-asterion, pterion-asterion) display a relatively large 12.5%increase along an anterior-medial-inferior to posterior-lateral-superior direction and a decrease about 5% along an anterior-

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TABLE 3. Results of finite element scaling analysis of normal into reshaped average Songish crania after correction to equal total volume' Landmark Cranial vault Bregma Bregma-lambda Lambda Lambda-opisthion Opisthion Pterion-aster. midpoint Pterion (R) Pterion (L) Bregma-pterion (R) Bregma-pterion (L) Bregma-asterion (R) Bregma-asterion (L) Pterion-asterion (R) Pterion-asterion (L) Asterion (R) Asterion (L) Cranial base Jugular process (R) Jugular process (L) Foramen lacerum (R) Foramen lacerum (L) Optic foramen midpoint Vomer spine Infratemporal crest (R) Infratemporal crest (L) Face Fronto-malare (R) Fronto-malare (L) Zygomaxillare sup. (R) Zygomaxillare sup. (L) Nasion Nasale Intradentale superior Posterior nasal spine Maxillary tuberosity (R) Maxillary tuberosity L) Premaxilla-maxilla (R) Premaxilla-maxilla (L) Global Element Lower face (R) Lower face (L) Upper face (R) Upper face (L) Cranial base Posterior vault (R) Posterior vault (L) Anterior vault (R) Anterior vault (L)

-

Size (Prob)

Shape (Prob)

PV1 (Dir)

PV2 (Dir)

PV3 (Dir)

1.13 (0.308) 0.93 (0.444) -2.87 (0.999)' -3.14 (0.724) -3.07 (0.874) -0.73 (0.848) 0.38 (0.476) 0.15 (0.518) 0.72 (0.444) 0.73 (0.390) 4.16 (0.132) 3.68 (0.001)' 5.49 (0.142) - 1.00 (0.658) 1.70 (0.180) 2.64 (0.086)

4.69 (0.426) 6.12 (0.538) 6.05 (0.016)' 6.66 (0.182) 10.24 (0.001)' 8.24 (0.010)' 7.62 (0.038)' 6.81 (0.028)' 5.58 (0.442) 6.56 (0.334) 12.31 (0.004)' 5.32 (0.660) 23.94 (0.018)2 13.59 (0.036)' 7.83 (0.044)' 4.28 (0.514)

7.5 (M-L) 9.8 (M-L) 5.5 (M-L) 5.8 (AOI-PRS) 10.7 (AOI-PRS) 11.7 (M-L) 10.5 (M-L) 8.9 (AMS-PLI) 8.4 (AMS-PLI) 7.7 (AMS-PLI) 25.2 (AMI-PLS) 12.5 (AMI-PLS) 43.4 (ALS-PMI) 14.3 (ALI-PMS) 12.1 (AMI-PLS) 8.0 (ALI-PMS)

0.9 (AOS-PRI) -0.3 (AS-PI) -4.2 (ARI-POS) -4.0 (AR-PO) -3.5 (ARI-POS) -3.7 (ARI-POS) 0.7 (ALS-PMI) 0.7 (ALS-PMI) 0.2 (M-L) 3.4 (ALS-PMI) 1.4 (AS-PI) 0.4 (MS-LI) 13.2 (AMI-PLS) 4.2 (AMI-PLS) 2.6 (AMS-PLI) 3.5 (AM-PL)

-4.3 (A-P) -5.6 (AOI-PRS) - 8.6 (AS-PI) -9.7 (S-I) -13.2 (AS-PI) -8.2 (AS-PI) -8.3 (AI-PSI -7.8 (AI-PSI -5.5 (AI-PS) -7.6 (AI-PS) -8.5 (ALI-PMS) -0.5 (ALS-PMI) -20.5 (MS-LI) -16.2 (Asmi - 7.7 (ALS-PMI) -2.9 (ALS-PMI)

1.19 (0.344) 4.90 (0.116) -5.93 (0.730) -2.04 (0.582) -5.09 (0.940) -0.87 (0.718) -1.26 (0.684) 1.86 (0.332)

14.64 (0.012)2 4.95 (0.632) 48.45 (0.012)' 23.82 (0.016)' 13.96 (0.060)3 5.81 (0.132) 4.83 (0.772) 8.30 (0.528)

21.6 (MI-LS) 12.0 (S-I) 83.2 (AL-PM) 18.2 (AMS-PLI) 12.7 (M-L) 6.7 (M-L) 4.6 (M-L) 14.1 (M-L)

3.5 (AM-PL) 5.7 (A-P) 2.1 (AMS-PLI) 16.3 (AL-PM) -3.6 (AS-PI) -0.9 (A-P) -0.9 (A-P) 1.0 (A-P)

-14.9 (ALI-PMS) - 1.4 (M-L) -37.4 (AI-PS) -25.5 (AI-PS) -18.3 (AI-PSI -7.4 (S-I) -6.9 (S-I) -7.3 (S-I)

6.81 (0.044)3 4.86 (0.080) -3.87 (0.876) 4.00 (0.188) 2.88 (0.038)3 0.81 (0.324) -2.95 (0.888) -1.10 (0.816) -3.24 (0.764) -4.30 (0.824) -0.69 (0.616) -3.91 (0.910) 0.08 (0.538) Volume difference -6.88 (0.920) -2.50 (0.662) 3.03 (0.282) 4.44 (0.126) 1.04 (0.460) -5.95 (0.818) -2.55 (0.672) 1.05 (0.416) 3.99 (0.054)

17.73 (0.082)3 10.73 (0.218) 5.67 (0.774) 5.12 (0.876) 7.41 (0.224) 4.30 (0.292) 4.12 (0.402) 6.34 (0.574) 7.05 (0.472) 10.87 (0.234) 5.92 (0.536) 6.01 (0.272) 0.10 (0.474)

41.4 (AS-PI) 23.4 (AS-PI) 1.2 (AI-PSI 11.1 (M-L) 13.8 (AI-PS) 4.7 (AI-PSI 1.8 (AO-PR) 6.4 (AOI-PRS) 4.0 (AM-PL) 8.6 (AM-PL) 5.4 (M-L) 4.5 (A-P)

3.2 (AMI-PLS) 2.2 (AMI-PLS) -0.9 (AMS-PLI) 4.7 (AMS-PLI) 2.4 (AR-PO) 3.3 (M-L) -2.3 (AR-PO) 0.1 (AR-PO) -0.7 (ALS-PMI) -2.3 (AL-PM) 1.6 (A-P) -5.7 (S-I)

-11.3 -6.3 -10.5 -2.4 -5.6 -5.0 -7.6 -8.6 -11.3 -15.5 -8.1 -9.0

(M-L) (ALI-PMS) (AL-PM) (AI-PS) (AS-PI) (AS-PI)

(S-I) (AS-PI) (S-I) (S-I) (S-I) (M-L)

'Measurements reported include size and the proportion of bootstrap samples displaying a larger difference than the observed one (a two-tailed test so that landmarks with proportions greater than 97.5% are significantly smaller than normal while those with a proportion less than 2.5% are significantly larger); shape and the proportion ofhootstrap sample showing larger shape differences than those observed (one-tailed test); the three principal values (PVi) and their associated anatomical dimensions (Dir) (A, anterior; P, posterior; M, medial; L, lateral; S, superior; I, inferior; and for midline points R, right; 0, left). Also provided are the proportional differences in volume between unmodified and modified crania. 'Indicates statistically significant a t the 5% level. %dicates statistically significant a t the 10%level.

lateral-superior to posterior-medial-inferior axis. Pterion-asterion had a unique shape change with very large increases along an anterior-lateral to posterior-medial axis and

large decreases in the anterior-superior to posterior-inferior dimension. The shape changes along the midline and in the anterior and posterior cranial vault

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339

B

Fig. 8. Finite element scaling results of the deformation of normal and modified Songish males drawn on the normal average Songish male cranium. Ellipses represent magnitudes and directions of difference between the normal and modified Songish. Ellipses are exaggerated by a factor of 2 to aid in interpretation. Ellipses which appear as straight lines indicate extreme shape change. A Basal view. B: Lateral view.

are directly opposed to one another, with size increasing at pterion and bregmapterion along dimensions which are decreasing for midline and posterior-lateral landmarks. Furthermore, pterion-asterion also

changes shape in opposition to surrounding landmarks. These opposed shape changes lead to a shearing of the entire cranium and contrast with the homogeneity of transformation displayed by the Ancon crania.

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The posterior cranial base has several significant shape changes at the jugular process and at foramen lacerum. However, the shape changes are quite different at these two landmarks, again resulting in a sheared cranial base. At the jugular process there is a 20%medial-inferior to lateral-superior increase and a 15%anterior-lateral-inferior to posterior-medial-superior decrease. In contrast, at foramen lacerum there is a large 50% anterior-lateral to posterior-medial increase coupled with a 30% anterior-inferior to posterior-superior decrease, as in the anterior-lateral cranial vault. The anterior cranial base displays a 9.5% mediolateral increase and a 7% superior-inferior decrease. The face has only one significant shape difference, at the left fronto-malare. In the upper lateral face, fronto-malare shows a very large 30%increase in an anterior-superior to posterior-inferior direction and a 6% decrease in an anterior-lateral-inferior to posterior-medial-superior direction. Zygomaxillare superior also shows an anteriorlateral to posterior-medial decrease of about 5%.The upper facial midline landmarks, nasion and nasale, increase 10%along an anterior-inferior to posterior-superior axis and decrease 5% along an anterior-superior and posterior-inferior axis. The lower facial landmarks decrease 9.5% along a superiorinferior dimension and typically increase about 5% mediolaterally, making for a shorter-wider lower face.

cranial base. Functional competence must be maintained by the continued connection between these parts of the skull. The widening cranial base results in a general anterior-posterior reduction in facial dimensions, particularly in the maxillary alveolus and nasal regions. Furthermore, the upper, orbital portions of the face are drawn down and inwards towards the cranial base. Rather surprisingly, the amount of difference between normal and modified groups is not very diverse across the various regions of the skull. Average shape change was 3.82 for the vault, 3.49 for the base, and 3.38 for the face. Likewise, typical percentage increases and decreases along extreme principal axes were about 5% in all parts of the cranium. These differences are more visually obvious in the neurocranial vault because the vault is much larger than the face, comprising 84% of the volume of all the finite elements. Thus, while vault differences are much larger in absolute terms, they are nearly the same as facial differences in proportional terms. We can describe these cranial modifications with a simple geometric model, treating the braincase as a quadrilateral and the face as a triangle (Fig. 9). We will describe this in a two-dimensional view for the sake of clarity, although the processes referred to occur in all three dimensions. The normal skull is shown with a rectangular braincase, the anterior wall representing the cranial base. The cranial base also forms the base of a triangle representing the face. Fronto-ocDISCUSSION cipital flattening results in the widening Fronto-occipital flattening of the cranial and anterior-superior to posterior-inferior vault has a significant indirect effect on the shortening of the braincase. This involves a cranial base and face in the Ancon. The widening of the cranial base. Since the craphysical reshaping of the neurocranial vault nial base forms the base of the facial trianresults in a series of compensatory bony gle, its increased width requires a decrease changes required for normal neural growth. in anterior-posterior dimensions. The obThe size of the neurocranial vault remains served 5%anterior-posterior decrease in the the same. The restriction of growth between faces of modified skulls is approximately the the frontal and occipital bones results in a amount required by the observed widening compensatory increase mediolaterally be- of the cranial base. A similar model was tween the parietal bones. This is accompa- used to describe the effects of fronto-occipinied by a widening of the anterior cranial tal flattening on mandibular morphology base and a shallower posterior cranial base. (Cheverud and Midkiff, 1992). These results confirm and extend the obSince facial size is unchanged by fronto-occipital flattening, it must also change shape servations of previous workers concerning to compensate for the increased width of the fronto-occipitalflattening. The most compa-

ARTIFICIAL C F KVIAL. RESHAPING

341

along an anterior-lateral-superior to posterior-medial-inferior axis (nearly parallel to a line connecting fronto-malare to the vomer spine) could not be compared to Anton’s (1989) results because she was not able to include any measurements paralleling this dimension. This deficiency, along with the general deficiency in anterior-posterior linear measurements, is a result of following traditional measurement protocols which in turn are based on distances between landmarks which can be comfortably spanned by calipers. However, morphological differences between forms may not be restricted to dimensions which can be recorded with calipers. An advantage of collecting data as three-dimensional coordinates and performing finite element scaling analysis is that Fig. 9. Geometric model representing the cranium the dimensions along which we can detect (quadrilateral) and face (triangle). Fronto-occipital mod- and quantify morphological variability are ification results in shortening of the cranium along the not limited to those which can be spanned by antero-superior t o posterior-inferior dimension and wid- a caliper. The three-dimensional morphologening of the cranium along the mediolateral dimension. Modification of the face is required for the face to con- ical dimensions of greatest variability are identified and quantified in finite element from to the cranial base. scaling (Cheverud and Richtsmeier, 1986). Furthermore, even when a caliper can span rable study is Anton’s (19891, which used a morphological dimension, standard measome specimens from the Ancon series surement protocols have tended to collect which were not included here and was re- measurements in generally anterior-postestricted to Peruvian samples. Nearly all of rior, mediolateral, or superior-inferior diher significant differences in linear mea- mensions. If the morphological dimensions surements were in mediolateral orientation, which are most different between the groups including biorbital, interorbital, orbital, bi- compared do not happen to fall along these maxillary, bizygomatic, and cranial base axes, as is often the case here, real morphobreadth. We also found increased anterior logical differences between groups may be cranial base width of about 5%, a similar hidden or grossly underestimated. The results for the Songish are based on magnitude to that found by Anton (1989) and generally increased widths across the small samples and are often not statistically face. We did not find an increase in facial significant. Even so, the results often consize along an axis corresponding to the 4% flicted with those for the Ancon, even increase in nasion-prosthion height re- though both are assigned to the same class ported by Anton (1989) (see Fig. 5). Her trait of artificial modification, fronto-occipital set only included one anterior-posterior di- flattening. Superimposed modified average mension, palate length, which was not sig- Ancon and Songish crania are displayed in nificantly different in her comparisons. This Figure 10 after increasing the Ancon skull’s contrasts with our general finding of ante- volume to match that of the Songish. The rior-posterior facial reduction, especially in modification is more severe in the Songish the maxillary alveolus. She also did not find than in the Ancon. There were also distinct an increase in palatal breadth, although we differences from normal in the two groups. found significant mediolateral increases in While the Songish midline cranial vault landmarks followed the same pattern found the lower face. The most striking change in facial mor- throughout the Ancon cranial vault, mediophology reported here, the 7% decrease lateral increase and anterior-superior to

ip

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Fig. 10. Superimposition of average modified Ancon (solid line) and average modified Songish (broken line) after Procrustes registration of all landmarks. The average modified Ancon male was increased in size to equal the size of the average modified Ancon male. A Basal view. B: Lateral view.

posterior-inferior decrease, the lateral cra- terior-superior to posterior-inferior). This nial vault in the Songish is modified in a results in less of a box-shaped cranial vault complex fashion. Neighboring landmarks in the modified Songish as compared with increase in size along opposed morphologi- the modified Ancon. cal dimensions with pterion and bregmaThe cranial base changes which accompterion even increasing along the dimension pany fronto-occipital flattening in the two orthogonal to the deforming appliance (an- groups are quite similar, including the me-

ARTIFICIAL CRANIAL RESHAPING

diolateral increase in anterior cranial base landmarks. However, there are several differences in facial changes relative to normal crania in the two groups. The anterior-superior to posterior-inferior increase seen at pterion and bregma-pterion in the Songish is also observed along the lateral orbital rim at fronto-malare. This contrasts strongly with the results from the Ancon. However, anterior-lateral to posterior-medial decreases are seen in both groups in the lateral face. The lower facial landmarks show a mediolateral increase in both groups, although the Songish decrease along a superior-inferior dimension, not along the anterior-posterior dimension as observed in the Ancon. The differences between the Ancon and Songish modifications could arise from several sources. The Songish are more severely modified which may require more compensatory growth in the lateral neurocranium and lead to the different anterior-lateral neurocranial vault morphologies observed in the two populations. This difference in vault reponse to the modification could also be responsible for the differences in facial response observed, even though the cranial base responds in a similar fashion in both populations. The differences in response to modification could also be due directly to the different appliances used by the two groups. The bands shown for Huari Empire headdress (Allison et al., 1981) and the Songish cradle (Boas, 1891) are fairly different devices (see Fig. 1).The Songish cradle board is open laterally while the Ancon headdress includes a band running around the lateral sides of the head. The cradle, being open laterally, may have allowed some anteriorposterior compensatory growth laterally, as seen at pterion and bregma-pterion. Regardless of the cause of the differences in response to modifying appliances in these two populations, fronto-occipital flattening does not appear to be a unitary phenomenon and its morphological effects may differ depending on the particular device and conventions used in applying it. One should be careful in using these results across broad classes of artificial cranial reshaping. Instead, generalization should be restricted to similar extents and types of modification within local cultural traditions.

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In addition to uncovering dimensions which are very different between normal and artificially modified crania, finite element scaling identifies dimensions which differ only a little or not at all due to artificial modification. In the Ancon cranial vault the anterior-inferior t o posterior-superior dimension is only 0-1% different in most landmarks (an average of 0.6%). This dimension also shows relatively little change in the cranial base. In the face, anteriormedial to posterior-lateral and anterior-latera1 to posterior-medial dimensions are only slightly different between groups. These dimensions would be suitable for comparing populations including modified crania. The results presented here have more general implications for human cranial growth and evolution. Fronto-occipital flattening of the cranial vault in the Ancon leads to a cascade of developmental effects on the growing cranial base and face resulting in a wider cranial base and a foreshortened, wider face. This indicates that the growing parts of the cranium are not largely independent, as suggested by functional cranial analysis (Moss, 19731, although it is clear that there is still much freedom for facial variation independent of cranial vault form. The proportional magnitude of the effects observed here is likely to be on the order of magnitude of evolutionary transformations in the human lineage, indicating that primary evolutionary changes in vault shape would have important effects on the face and cranial base. When we consider gross changes in cranial morphology during human evolution, we should consider the effects of changing cranial vault shape on the face rather than treating these variations independently. Our “natural experiment” in human cranial growth does not allow us to specify the effects of primary evolutionary changes in the face on the cranial vault. In general evolutionary terms, it is likely that genetic and environmental effects on morphology mimic one another by operating through the same, relatively invariant, developmental system (Cheverud, 1988). Based on the results of quantitative genetic studies, we expect that modifications to the growth of the cranial vault, whether due to the application of external appliances (as in this study), genetic mutations, or other envi-

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ronmental factors, will also have some effect on the growth of the cranial base and face. Cheverud (1982) found genetic correlations between cranlal vault and facial traits in rhesus macaques which may arise through epigenetic mechanisms similar to those documented here. Thus, with facial size held constant, we predict that a gene, or set of genes, which results in a wider brain will also typically result in a wider neurocranial vault, a wider anterior cranial base, and a foreshortened, wider face just as we found that a constraining appliance has these effects. New methods in quantitative and molecular genetics will allow tests for such pleiotropic single gene effects (Cheverud, 1993). ACKNOWLEDGMENTS We thank Dr. Glenn Cole and the Field Museum of Natural History for access to skeletal material. We also thank Dr. Joan T. Richtsmeier for making FIESCA available to us, and Nyuta Yamashita and Jim Midkiff for help in collecting the data. This research was supported by NSF grant BNS 89-10998. LITERATURE CITED Allison M, Gerszten E, Munizaga J, Santoro C, and Focacci G (1981) La practica de la deformacion craneana entre 10s pueblos Andinos Precolombinos. Chungara 7:23&260. Anton SC (1989) Intentional cranial vault deformation and induced changes of the cranial base and face. Am. J. Phys. Anthropol. 79r253-268. Bennett KA (1961)Artificial cranial deformation among the Caddo Indians. Tex. J. Sci. 13:377-390. Bennett KA (1965) The etiology and genetics ofwormian bones. Am. J. Phys. Anthropol. 23:255-260. Bjork A, and Bjork L (1964) Artificial deformation and cranio-facial asymmetery in ancient Peruvians. J. Dent. Res. 43:353-362. Blackwood B, and Danby PM (1955)A study of artificial cranial deformation in New Britain. J. R. Anthropol. Inst. 85:173-192. Boas F (1891) Second general report on the Indians of British Columbia. Rep. British Assoc. Advancement Sci. 60562-715. Bookstein FL (1978) The measurement of biological shape and shape change. Lecture Notes in Biomathematics, No. 24. New York: Springer-Verlag. Bookstein FL (1983) The geometry of craniofacial growth invariants. Am. J. Orthod. Dentofacial Orthop. 83:221-234. Bookstein FL (1984) A statistical method for biological shape change. J . Theor. Biol. 107:475-520. Bookstein FL (1986)Size and shape spaces for landmark data. Stat. Sci. 1:181-242.

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