Morphological Variation

A summary of the t-test results is given in Table 20. Sixteen chords, three angles and five indices exhibit significant mean differences for at least one regional pair. Further discussion of these results deals first with the chord variables alone, then with the angle and index variables.

Chord variables

Of the 16 chord variables displaying significant regional mean differences, five are either unrelated measurements in terms of the morphological features they describe, or they are significantly variable over only one or two dichotomous regional pairs. These are maximum bi-parietal breadth (MA-ER, CG-ER), minimum postorbital breadth (NK-ER), glabella prominence (CG-ER, NK-ER), cheek height (MA- CG, CG-NK) and nasospinale-prosthion (CG-NK) . The remaining 12 chord measurements display individually regular patterns of significant variation throughout the six regional pairs. When these are jointly considered, they indicate a generally regular pattern of significant

Table 20. Summary of individual variable mean comparisons for each of six Central Highland regional pairs. An asterisk indicates the regional pair shows significant differences for t at p < .05

Regional Pairs

Variable MA-CG MA-NK MA-ER CG-NK CG-ER NK-ER

G l a b e l l a - o p i s t h o c r a n i o n * * * M a x i m u m b i - p arietal br. B i -auriculare * * B a sion-bregma M a x i m u m supraorbital br. * * M i n i m u m p o s t o rbital br. N a s i o n -bregma * M e t o p i o n height * * N a s i o n - m e t o p i o n * * * * Glabella prominence * ★ Lambda-bregma * * * * Parietal subtense h t . * * * * Bregma- p a r i e t a l subtense M a s t o i d length L a m b d a -asterion L ambda-inion B a s i o n -lambda A u r i c u l a r e - b a s i o n * * F o r amen m a g n u m length F o ramen m a g n u m breadth N a s i o n - p r o s t h i o n Bi-zygion N a s i o n - n a s o spinale Nasal breadth * * Cheek, height Orbital height Orbital b r e adth B i - m a x i l lofrontale * * Naso f r o n t a l articulation Al v e o l a r length Al v e o l a r breadth * * * B a s i o n-nasion * * * * Basion-n a s o s p i n a l e Basion- p r o s t h i o n * * * N a s o s p i n a l e - p r o s t h i o n ★ P r o s thion angle * * * * N a s o s pinale angle * Subnasal angle Cranial module * * * * * Cranial index * * * *

Frontal curvature index * * *

Parietal curvature index U p per facial index

Orbital index * * * * Nasal index M a x i l l o - a l v e o l a r index * * * Gnathic index * * * *

variation throughout the Division for a number of morphological features. These are vault length, sagittal vault curvature and elements of facial breadth and facial prognathism.

Nebilyer-Kaugel is distinguished from the other three regions by a regularly greater mean vault length (glabella-opisthocranion) . None of the other three regions is significantly different for this variable.

Mariko is distinguished from the other three regions by a significantly narrower supraorbital region (maximum supraorbital breadth and nasofrontal articulation) and a broader nasal aperture (nasal breadth). None of the other regions is significantly different for these three variables.

A complex pattern of regional variation in sagittal vault curvature is indicated by a number of chord variables. Regional variation in the form of the frontal is indicated by significant differences in metopion height (MA-CG and MA-NK) and nasion-metopion (MA-CG, MA-ER, CG-ER and NK-ER). Mariko is generally distinguished by its greater absolute frontal curvature height and Erave by its more anteriorly located point of maximum frontal curvature, although both Mariko and Chimbu Gorge are also somewhat variable for this latter

feature.

Regional variation in the form of the parietal is indicated by significant mean differences in both lambda-bregma length and parietal subtense height (MA-NK, MA-ER, CG-NK and CG-ER for both variables) and in bregma-parietal subtense length (CG-NK and CG-ER) . If only the first two variables are considered, there is no apparent separation of any one region from the others, but if all three variables are considered together, Chimbu Gorge is distinguished by parietals of

intermediate curvature but with the point of maximum curvature located more anteriorly.

Lastly, significant mean differences in basion-nasion (MA-CG, MA- NK, MA-ER and CG-NK) and basion-nasospinale (MA-CG, MA-NK and CG-NK) indicate regional differentiation in the degree of facial prognathism. Mariko, Chimbu Gorge and Nebilyer-Kaugel are characterised by significant and regularly increasing mean values for both variables and, given a lack of significant variation in basion-prosthion length, the regional trend might be expected to show decreasing degrees of facial projection from Mariko in the east to Nebilyer-Kaugel in the west.

Angle and index variables

The angle and index variables tend to confirm the patterns described for related morphological features identified by the chord variables. A lack of significant regional variation in the cranial module indicates generally uniform vault size throughout the Division. However, significant variation in the cranial index (MA-CG, MA-NK, MA- ER and CG-NK) certainly differentiates Mariko from the other three regions on the basis of its greater mean vault breadth. Nebilyer- Kaugel is also distinguished as a result of its greater vault length.

Significant variation in nasal breadth which differentiates Mariko from the other regions is reflected by variation in the nasal index (MA-CG, MA-NK and NK-ER). There does not appear to be any significant variation in overall upper facial shape however (neither the upper facial index nor the orbital index are regionally variable), and variation in facial breadth is therefore confined to the nasal and

supraorbital regions (identified by the individual chord measurements).

Regional variation in the degree of sagittal vault curvature is also indicated by variation in both the frontal (MA-CG, MA-NK, MA-ER) and parietal (MA-NK, MA-ER, CG-NK and CG-ER) curvature indices, although now a geographically regular pattern is evident in the former. Mariko is distinguished by a significantly greater degree of frontal curvature, the other three regions being similar with no significant variation indicated. The parietal curvature index remains significantly variable throughout the entire Division and indicates a regularly increasing degree of posterior sagittal vault curvature from Mariko in the east to Erave in the west.

Variation in the degree of facial prognathism is also indicated by significant variation in the gnathic index (MA-CG, MA-NK, MA-ER and CG-ER), the prosthion angle (MA-CG, MA-NK, MA-ER and CG-ER) and the subnasal angle (MA-CG, MA-NK, MA-ER, CG-NK and CG-ER). An identical pattern of variability for the prosthion angle and the gnathic index is to be expected, given that they are computed from the same three chord measurements and measure the same morphological feature. Together, they distinguish Mariko from the other three regions on the basis of its greater degree of general upper facial prognathism. A regularly decreasing degree of facial prognathism from east to west, postulated earlier, is reflected by the pattern of significant subnasal angle variation.

It is interesting to note that the nasospinale angle is significantly different for only a single regional pair, Chimbu Gorge- Nebilyer-Kaugel. This indicates that differences in overall facial prognathism are largely subnasal in origin.

5.2.3.4 Summary

In summary, it is possible to draw a number of conclusions concerning regional craniometric variation within the Central Highlands Division on the basis of significant regional pairwise mean differences for a number of chord, angle and index variables:

1. The Division is generally homogeneous for most aspects of vault