Abstract
Despite numerous papers addressing the topic, the gross morphology of the ratite tongue and more specifically that of the emu, has been superficially or poorly described. This paper presents the first definitive macroscopic description of the emu tongue and reviews, consolidates and compares the scattered information on the gross morphology of the ratite tongue available in the literature. Twenty-three heads obtained from birds at slaughter were used for this study. Specimens were fixed in 10 % neutral buffered formalin, rinsed and the gross anatomy described. The emu tongue is divided into a body and a root. The body is triangular, dorsoventrally flattened, pigmented and displays caudally directed lingual papillae on both the lateral and caudal margins. The root, a more conspicuous structure in comparison to other ratites, is triangular, with a raised bulbous component folding over the rostral part of the laryngeal fissure. Following the general trend in ratites, the emu tongue is greatly reduced in comparison to the bill length and is specifically adapted for swallowing during the cranioinertial method of feeding employed by palaeognaths. This study revealed that it is not only the shape of the tongue that differs between ratites, as previously reported, but also its colour, appearance of its margins and root, and its length in comparison to the bill, and the shape of the paraglossum.
Highlights
The gross morphological features of the avian tongue have been described in numerous species and the structural adaptations of this organ linked to diet and mode of feeding (Gardner 1926, 1927)
Harrison (1964), on the other hand, proposed the classifica tion of avian tongues into five functional groups, namely tongues specialized for collecting food, eat ing, swallowing, taste and touch, and nest building
Echoing the suggestion by Gardner (1926, 1927) that microscopic data would enhance the under standing of macroscopic features, recent studies have generally supplied more comprehensive infor mation on the structure of the avian tongue by using both light and electron microscopy in addition to macroscopic descriptions (Kobayashi, Kumakura, Morphology of tongue of emu (Dromaius novaehollandiae)
Summary
The gross morphological features of the avian tongue have been described in numerous species (see McLelland 1979 for a review of the earlier lit erature) and the structural adaptations of this organ linked to diet and mode of feeding (Gardner 1926, 1927). During the past 180 years numerous publications on the ratite tongue have appeared in the form of sketches, descriptions and comparisons (Meckel 1829; Cuvier 1836; Gadow 1879; Owen 1879; Py craft 1900; Göppert 1903; Duerden 1912; Faraggi ana 1933; Roach 1952; Feder 1972; McCann 1973; Cho, Brown & Anderson 1984; Fowler 1991; Bonga Tomlinson 2000; Gussekloo & Bout 2005; Porches cu 2007; Crole & Soley 2008; Jackowiak & Ludwig 2008; Tivane 2008) Many of these studies, how ever, provide incomplete and sometimes mislead ing information on the macroscopic features of this organ. This study contributes to a better understanding of the upper digestive tract of the emu and provides data that can be used for more meaningful future comparative studies of the ratite tongue
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