Visualizing the Unbalanced World of Domestic Dogs: An Interactive Examination of the Canid Vestibular System

Abstract

The bony labyrinth (BL) of the petrous contains the organs responsible for balance (vestibular system) and hearing (cochlea). The vestibular system is comprised of three semicircular canals (which detect angular acceleration of the head) and two otolith organs (for detecting linear acceleration and static tilt). Studies in mammals have shown that semicircular canal morphology reflects sensitivity to angular acceleration, particularly canal orientations at right angles to one another (orthogonality). Due to their significant variation in craniofacial form while exhibiting similar locomotion, canids provide an excellent natural experiment to understand the influence of shape on vestibular morphology. This study expands upon our earlier analyses on relationships among BL size, cranial base length and semicircular canal morphology across dog breeds and creates an interactive three‐dimensional (3D) model of the canid cranium and BL to visualize relationships among variables. A portion of the sample is derived from the comprehensive study by Schweizer et al. on canid inner ear metrics (2017). Results show that orthogonality between the anterior and posterior semicircular canals is significantly correlated with BL size and cranial base length, suggesting their intimate association across dog breeds. Small, highly derived breeds, such as the short‐faced pug, had anterior and posterior semicircular canals that deviated the most from orthogonality. Similarly, due to their compressed cranial form, such highly bred domestic dogs may also be expected to exhibit altered vestibular function. Our interactive 3D model will allow visualization of statistically significant relationships among BL size, cranial base length and semicircular canal morphology among the breeds. The model will show predicted correlated change in the bony labyrinth based on cranial dimensions. In addition, the visualization will allow the prediction of intermediate and extreme semicircular canal morphologies by manipulating the dimensions of the model itself. By constructing such a model, we hope to lay the foundation for future research into visualizing the morphological integration of inner ear tissues and cranial architecture.Support or Funding InformationThis research was supported by The Graduate Center, City University of New York through a Graduate Center Fellowship; the New York Consortium in Evolutionary Primatology; and the Center for Anatomy and Functional Morphology, Icahn School of Medicine at Mount Sinai.