The assessment of the relationship between the traits of temporal muscle and the massiveness of the supraorbital region of the Homo sapiens crania including the influence of the neurocranial shape and size of the occlusal surface of the upper molars – preliminary study

The knowledge about the pattern of the relationship between the morphological variability of the supraorbital region of human skulls and the features of the temporal muscle is far from complete. The main aim of this study was to determine the relationships between the traits of human temporal muscle (i.e., its relative height and length) and the relative massiveness of the supraorbital region of the frontal bone with taking into account the potential influence of the neurocranial shape and the relative area of the occlusal surface of the upper molars. Skulls of African and Australian males (n = 44) exhibiting high variability in the massiveness of the supraorbital region, the presence of two types of the upper molars (first and second, n = 88) and a good state of the preservation of the braincase with the clearly visible inferior temporal line were examined. The qualitative scales were used to assess the degrees of the massiveness of the supraorbital regions. Metric traits of temporal muscle and that used to calculate the index of the neurocranial shape, size of the braincase and the facial skeleton were collected. Values of the occlusal areas of the molars were obtained using the ImageJ software. Spearman’s rank correlation and partial rank correlation analyses were performed. The results of our study showed the relationships between the traits of the temporal muscle and only the degree of the robusticity of most lateral part of the supraorbital area (trigonum). However, when the influences of the neurocranial shape and the relative occlusal area of molars were excluded, these relationships disappeared. The greatest importance of the neurocranial shape for the formation of the morphology of the trigonum was indicated. The results of the study were discussed from the perspective of the potential role of the temporal muscle as the part of the mastication apparatus for the development of the robusticity of the cranial supraorbital region.