Abstract
BackgroundThe 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.ResultsIn 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.ConclusionsOnly 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.
Highlights
The avian glottis channels air from the oropharynx to the trachea and is situated on an elevated structure, the laryngeal mound
As the tongue was retracted, the smooth tongue root became highly folded and was effectively obliterated (Figure 3b) as the rostral portion of the laryngeal mound was encased by the pocket in the base of the tongue body (Figures 1c, 2b)
In the absence of an epiglottis, the wide glottis of ratites appears to be protected by the linguo-laryngeal apparatus and which may functionally replace the epiglottis
Summary
The avian glottis channels air from the oropharynx to the trachea and is situated on an elevated structure, the laryngeal mound. An epiglottis is reportedly absent in birds Ratites such as Struthio camelus and Dromaius novaehollandiae possess a very wide glottis in comparison to other birds. In this study we aim to marry the functional data on living Ratidae and morphological observations on fresh and preserved material to demonstrate how the intricate relationship between the variably structured tongue body, tongue root and laryngeal mound, of S. camelus and D. novaehollandiae, functions to close off and stabilise the glottis during swallowing, partially fulfilling the role of an epiglottis. It is demonstrated that this relationship in the living animal, with such perfectly fitting structures, cannot merely be explained away as a coincidence This unique proposed anatomical mechanism has tentatively been named the linguo-laryngeal apparatus
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