Aspects of the Ontogenesis of the Avian Columella Auris

Abstract

Observations on embryological material from Spheniscus demersus, Acridotheres tristis, Geopelia cuneata and Gallus domesticus strongly suggest that the avian stapes represents part of an infrapharyngohyal while the rest of the pharyngohyal material (supra- plus infrapharyngohyal) together with the epihyal and a secondary laterohyal component form the extracolumella. The latter structure bears three so-called processes: the supracolumellar arcade or process (de Beer's lateral prong) whose inner limb is derived from the suprapharyngohyal and the outer limb (comprising at least part of the intercalary) from the laterohyal blasteme; the tympanic process (extracolumellar process) also derived from laterohyal blasteme; and the infracolumellar process (formed by the distal tip of the epihyal and a composite interhyal) which is continuous with the ceratohyal in most birds. Our investigation suggests that the supposed great variation in the development of the columella among birds is a fallacy.