What prevents Struthio camelus and Dromaius novaehollandiae (Palaeognathae) from choking? A novel anatomical mechanism in ratites, the linguo-laryngeal apparatus

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.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.In mammals the glottis is protected and closed during swallowing mainly by covering it with the epiglottis, as well as the pulling together (adduction) of the cartilages on either side of the glottis. Birds, however, have a slightly different laryngeal cartilage arrangement to mammals, with both the thyroid and epiglottic cartilages being absent. Struthio camelus (ostrich) and Dromaius novaehollandiae (emu), in comparison to neognathous birds, possess a very wide glottis [1]. The question can therefore be asked [2] (and remains unanswered) as to how it is possible for these large birds to have such a wide glottis, with apparently little protection, and yet avoid inhalation of food particles and fluid. Despite feeding and drinking studies in Gallus gallus[3] and in palaeognaths [4,5] using cinematography and radiography, no attempt has been made to explain or demonstrate how the glottis is prot