The morphogenesis of the avian Columella auris with special reference to <i>Struthio camelus</i>

Abstract

The columella auris of the ostrich is derived as in the crocodile from three sources; the two upper segments of the hyoid arch (pharyngohyal and epihyal) and a laterohyal component. The latter contributes the homologue of the crocodilian suprastapedial (or lacertilian intercalary) as well as the tympanic process and the material of the lateral limb (which is not lacking as stated in the literature) of the lateral prong (supracolumellar arcade). Conditions in Struthio camelus confirm the views expressed by the authors in their paper on Crocodilus niloticus regarding the homologies of the columellar processes. The avian infracolumellar process represents the crocodilian infrastapedial plus the interhyal which in addition to primary arch material, includes a secondary subepidermal part. The ceratohyal (usually called stylohyal in the literature) remains attached to the columella through the infracolumellar process.