Characterisation of the supraorbital foramen and notch as an exit route for the supraorbital nerve in populations from different climatic conditions.

The aim of this study was to obtain morphological data on the supraorbital foramina and notches related to sex and side of the skull in populations from different climatic conditions. We assume that the type and frequency of these supraorbital structures may depend on the climatic conditions in which the population lived. Populations from colder regions should have a higher frequency of foramina and populations from warmer climates should have a higher frequency of supraorbital notches than other populations. This may be a result of adaptive changes and developmental responses to ambient temperatures, for prevention of heat loss in the supraorbital neurovascular bundle passing through these supraorbital structures. Localisation of the supraorbital neurovascular bundle is higher and deeper when it passes through the foramen than in the notch. A total of 1978 orbits from 989 skulls collected in three climatic regions: warm, temperate and cold, were analysed. The highest frequency of supraorbital foramina (35.4%) was in skulls from cold climatic conditions. In samples from warm climates, the frequency of supraorbital foramina was lowest (16.4%). In contrast, the frequency of supraorbital notches was highest in the sample from warm climates (54.5%), and lowest in the sample from cold climatic conditions (44.0%). Statistically significant differences in the frequency of supraorbital structures were found between cold climate sample and the other two samples (p<0.05). Our results suggest a relationship between the type of supraorbital structure and climatic conditions as an adaptation to cold climate and thermoregulatory processes concerning the human head. This research is of direct relevance to clinical practice, and drawing attention to the differences in the frequency of these supraorbital structures may help surgeons to avoid injuring the neurovascular bundles. These data and studies may also contribute to the understanding of the impact of climate on the morphology of modern European skulls.