The asymmetry and modularity of the hyoid bone

Abstract

Morphological variation is a result of interplay among multiple intervening factors. For hyoid bones, the shape and size differences have been scarcely covered in the literature and in majority limited to studies of sexual dimorphism or age dependency. To our knowledge, the human hyoid bone, in complete opposite to other cranial bones, has not been fully utilized to address development questions in terms of asymmetry or modularity. In the present paper, we used landmark-based methods of geometric morphometrics and multivariate statistical approach to study human hyoid morphology represented by the hyoid body and greater horns in a sample of 211 fused and non-fused bones. Within a sample variation analysis, we showed that the hyoid bone is, by nature, asymmetrical bone which exhibits both directional and fluctuating types of asymmetry and is composed of well-integrated anatomical elements for which the biomechanical load of attached muscles is the most determining factor of variation. Yet, the covariance and evidence of unequal amount of fluctuating asymmetry among modules suggests a certain degree of independence during early stages of development.