Role of Spatial Integration in the Morphology of the Bony Labyrinth in Modern Humans

Abstract

The bony labyrinth corresponds to the osseous wall of the inner ear, the hearing and balance organ located in the petrous pyramids, in the base of the cranium. The morphology of the labyrinth reflects phylogenetic and ecological signals. In hominoid primates, it is also influenced by its anatomical environment. The aim of this study is to determine whether, in the species Homo sapiens, the morphological relationships between the labyrinth and the skull result from geometrical constraints linked to equilibrioception, or from spatial constraints due to the inclusion of the inner ear in the petrous bone. Based on CT-scans of the skulls of adult individuals (n=30), two sets of 22 landmarks each were placed on the labyrinth and on the basicranium. The covariations between these two sets were investigated using twoblock partial least squares (2B-PLS) analyses. The shape of the labyrinth is significantly correlated with the cranial base, but not with the isolated temporal bone. This indicates that the morphology of the labyrinth mainly results from functional constraints. However, several observations suggest that spatial constraints also have an influence, especially on the cochlea. The associated changes in shape are consistent with the ontogenetic trend, but differ slightly from the phylogenetic trend. These covariations caution against exclusively ecological interpretations of the morphology of the labyrinth.