Sex determination from the foramen magnum: discriminant function analysis in an eighteenth and nineteenth century British sample

The successful identification of the deceased is vital to the progress of any forensic investigation. One of the principal biological traits to be established from skeletal remains is the sex of the individual. This becomes more difficult if only parts of a skeleton are found or if the bones are compromised by physical insults such as fire, explosions or violence. The basal region of the occipital bone is covered by a large volume of soft tissue and is therefore in a relatively well-protected anatomical position, and as such, classification of sex using the occipital bone may prove useful in cases of significantly disrupted remains. The aim of this paper is to evaluate manually recorded morphometric variables of the region of the foramen magnum using both discriminant function analysis and linear regression. The skulls utilised in this study were selected from the eighteenth to nineteenth century documented skeletal collection of St. Bride’s Church, Fleet Street, London. Adult human skulls n = 158 (♂82/♀76) were measured to derive statistical functions. The results demonstrated that significant sexual dimorphism is present in the cranial base of the St. Bride’s material. The correctly classified crania within this population ranged from 65.8% for univariate functions to 70.3% for multivariate functions within the cranial sample. Males were correctly classified at 70.7% and females at 69.7% using multivariate functions. The linear regression equations predicted sex in the cranial sample correctly for 76% of the males and 70% for the females using different variables; however, overall highest correct prediction percentage was only 68%. Cross-validation brought the percentage down in some cases, but it was concluded that, overall, the expression of sexual dimorphism in the foramen magnum region within the St. Bride’s population is significantly demonstrable, and therefore, this area of the skull should be considered useful in the identification of sex.