BACKGROUND: The avian glottis channels air from the oropharynx to the trachea and is situated on an elevated
structure, the laryngeal mound. It is imperative that the glottis be protected and closed during swallowing, which in
mammals is achieved by covering the glottis with the epiglottis, as well as by adduction of the arytenoid cartilages.
An epiglottis, however, is reportedly absent in birds. Ratites such as Struthio camelus and Dromaius novaehollandiae
possess a very wide glottis in comparison to other birds. The question therefore arises as to how these large birds
avoid inhalation of ingesta through a wide glottis, with apparently little protection, particularly as their feeding
method involves throwing the food over the glottis to land in the proximal esophagus.
RESULTS: In S. camelus when the glottis was closed and the tongue body retracted, the smooth tongue root
became highly folded and the rostral portion of the laryngeal mound was encased by the pocket in the base of the
\ − shaped tongue body. In this position the lingual papillae also hooked over the most rostral laryngeal
projections. However, in D. novaehollandiae, retraction of the tongue body over the closed glottis resulted in the
prominent, triangular tongue root sliding over the rostral portion of the laryngeal mound. In both S. camelus and D.
novaehollandiae these actions resulted in the rostral portion of the laryngeal mound and weakest point of the
adducted glottis being enclosed and stabilised.
CONCLUSIONS: Only after conducting a comparative study between these two birds using fresh specimens did it
become clear how specific morphological peculiarities were perfectly specialised to assist in the closure and
protection of the wide glottis. We identify, describe and propose a unique anatomical mechanism in ratites, which
may functionally replace an epiglottis; the linguo-laryngeal apparatus.