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.

Waarnemings op embriologiese preparate van Spheniscus demersus, Acridotheres tristis, Geopelia cuneata en Gallus domesticus dui sterk daarop dat die stapes by voSIs deel van 'n infrafaringohiale verteenwoordig terwyl die res van die faringohiale materiaal (supra- plus infrafaringohiale) saam met die epihihiale en 'n sekonddre laterohiale komponent die ekstrakolumella vorm. Laasgenoemde struktuur dra drie sogenaamde uitsteeksels: die suprakolumellaar-uitsteeksel of -arkade (‘lateral prong’ van de Beer) waarvan die ‘binnebeen’ van die suprafaringohiale afkomstig is en die ‘buitebeen’ (wat minstens 'n deel van die interkalare insluit) deur die laterohiale blasteem bygedra word; die timpaniese uitsteeksel of ekstrakolumellaar-uitsteeksel wat ook van die laterohiale blasteem afkomstig is; en die infrakolumellaar-uitsteeksel (gevorm deur die distale punt van die epihiale enn saamgestelde interhiale) wat by meeste vo荤is aaneenlopend met die keratohiale voorkom. Ons ondersoek dui daarop dat die vermeende groot variasie wat ten opsigte van die ontwikkeling van die kolumella by vofils sou bestaan, 'n dwaling is.