Os intermetatarseum: a heritable accessory bone of the human foot.

The os intermetatarseum is a relatively common accessory bone of the human foot located at the tarsometatarsal border between the first and second metatarsals. It can occur as an independent ossicle or as an osseous spur projecting from the proximal ends of the first two metatarsals, or the distal end of the first cuneiform. To determine the frequency of this congenital defect in native North American groups and East Asians from Japan, the skeletons of 846 Native Americans and 125 modern Japanese and Ainu were examined for the presence of the os intermetatarseum. The North American skeletons are from archaeological sites in various parts of Canada and the United States, including the Arctic coast, the Subarctic, the Aleutian Islands, the Northern Plains, the Illinois River area, and the Southwest. Overall frequencies ranged from no occurrence among the Arctic samples to 8% of individuals from Pecos Pueblo. Second metatarsal spurs occurred in particularly high frequencies among American Indians, whereas the East Asians were only found to have os intermetatarseums associated with the first cuneiform. Because pedigrees have shown the os intermetatarseum to be an inherited defect, its high frequency among some Native Americans may be due, in part, to a higher degree of genetic relatedness among the individuals in the North American samples than among the relatively modern East Asians.

Retromolar foramen of the human mandible.

Analysis of retromolar foramen (RMF) in a large series of mandibles (N 2500) was undertaken to provide descriptive statistics for this variant. RMF of diameter 0.5 mm or greater were scored. Consistent with other data on accessory canals in the facial skeleton, RMF was found to occur more commonly in native populations of North America than in other populations (Africa, Europe, India, northeast Asia). The ratio of bilateral to unilateral occurrences was shown to increase with population incidence, a pattern consistent with the theoretical model of an epigenetic (threshold "quasicontinuous") variant. Male-female differences were not found. Age profiles were characterized by a marked peak in the adolescent cohort. In some populations RMF showed a positive intertrait correlation with accessory mandibular foramen and with accessory mental foramen, but correlations with presence/absence of third molar and three-rooted first molar were not found. With refinements in scoring criteria and, ideally, better evidence of its heritability, RMF should be useful along with other minor cranial variants for ethnohistorical studies.

Temporal crest canal: case report and statistics on a rare mandibular variant.

A child's mandible retrieved from a North American archaeological site had an anomalous canal 2 mm in diameter and 10 mm long, opening posteriorly behind the temporal crest and anteriorly in the retromolar fossa. Radiographic analysis revealed a second canal passing down from the temporal crest canal (TCC) toward the molar roots. A survey of retromolar variants in a large skeletal series (N2391) revealed TCC present in 1.7% of all persons on average, ranging up to 23% in certain population samples. It appeared to be more common in males than in females and in native Americans than in other racial groups. From its location and orientation, TCC was inferred to have conveyed all or part of the buccal nerve. The clinical significance of this variant is that pain fibers from the molar roots joining the nerve as it runs in this canal would exit the bone behind the temporal crest, thus escaping anesthetization in routine injections for inferior alveolar and buccal nerve block.

An argument for the use of total side frequencies of bilateral nonmetric skeletal traits in population distance analysis: the regression of symmetry on incidence.

In population studies based on frequencies of bilateral nonmetric skeletal traits, the choice between sampling by individuals or by sides should depend less on the exigencies imposed by fragmentary remains than on fundamental assumptions about the biological meaning of symmetry/asymmetry. Though the latter has been interpreted in various ways, little attention has focused on the possibility that bilateral correlation is meaningful in quantifying genetic liability for a trait. Analysis of two independent mandibular features, mylohyoid bridge and suppressed third molar, in Indian and Eskimo population samples (total N congruent to 1,200) reveals a statistically significant pattern of increasing bilateral occurrence with increasing population incidence. This pattern is consistent with the theory that liability for a "quasi-continuous" variant is normally distributed with constant increment between thresholds on an underlying scale. According to theory, phenotypes with more pronounced expression (bilateral occurrence) have greater genetic potential than those with less pronounced expression (unilateral occurrence). Therefore, scoring traits in total left and right sides, by giving greater weight to bilaterally affected individuals, may provide a better estimate of the liability for the trait in the population. Viewed in a theoretical context broader than that of the sampling debate, this pattern of positive regression of symmetry on incidence means that prevalence of unilateral occurrence probably cannot be used to assess the relative strength of genetic versus nongenetic control of threshold variants.

Congruence of distance matrices based on cranial discrete traits, cranial measurements, and linguistic-geographic criteria in five Alaskan populations.

Biological distances (C.A.B. Smith's Measure of Divergence) based on 25 nonmetric skull variants have been compared with distances (Mahalanobis' D2) based on cranial measurements of four Eskimo populations representing the Yupik subdivision of the Eskaleut linguistic stock, and one Aleut population. The ranking of Measures of Divergence (pooled-sex samples) for ten pairwise comparisons is significantly correlated (Spearman's rs) with both the male and female rankings of the F-values of D2. In addition, the non-metric distances showed stronger concordance than the metric distances with a hierarchy based on linguistic and geographical affinities. These findings indicate that, depending upon the particular battery of variants used, discrete traits provide valid taxonomical information in the study of extinct human populations.

Within and between race distances in population studies based on discrete traits of the human skull.

A battery of 24 discrete cranial traits has been tested for its power to discriminate within- and between-race distances for the two principal North American indigenous populations: Indian (7 samples, N = 366) and Eskimo (7 samples, N = 451). One of the Indian samples, Dakota Sioux, has been split according to tribal subdivisions, the intra-tribal mean distance providing a parameter of very close relationship. In addition, two Negro samples provide a parameter of relationship phylogenetically remote from the Amerinds. Separate male-female analysis of the three largest samples indicates that distances for pooled samples are not seriously affected by the sex component. Within-race distances (C. A. B. Smith's Measure of Divergence, MD), are smaller than between-race at the .00001 level of significance (Mann-Whitney U test) for both Indian-Eskimo and Amerind-Negro comparisons. The features most powerful for Indian-Eskimo and Amerind-Negro comparisons. The features most powerful for Indian-Eskimo discrimination are revealed by their percent contribution to the mean of 49 MD's. The African heritage of American Blacks is reflected in a characteristic Negro pattern of trait frequencies different from the Amerind. This battery of features yields valid taxonomical information useful in conjunction with other physical data to reconstruct affinities of extinct populations.