Despite numerous morphological studies on the avian tongue, very little meaningful information is currently available on the surface features of this organ using scanning electron microscopy (SEM). The only SEM description of a ratite tongue is that of the ostrich, although the descriptions are brief and superficial. This SEM study of the emu tongue confirms and compliments the comprehensive macroscopic and histological data available for this commercially important species. The tongues of five emus were fixed, cut into blocks representing the dorsum, ventrum and root and routinely processed for SEM. Three morphologically distinguishable surface types (desquamating, non-desquamating and lymphoepithelium) related to peculiarities in surface cell shape and status (desquamating or non-desquamating), cell surface modifications and distribution of gland openings, and which showed a regional distribution, could be identified. Three basic types of cell surface modifications (microplicae, microvilli and cilia) were observed, with microvilli and cilia being described for the first time in an avian tongue by SEM. The desquamating surface cells fulfil a mechanical protective function, whereas the microplicae, microvilli and cilia appear to be adaptations for the trapping and spreading of mucus which also fulfils a protective function.

Information on the gross morphology of the upper digestive tract of ratites is sparse. This is an important region considering that it is the first area for food selection and intake which is vital to the nutrition and growth of the animal and therefore its commercial viability. Twenty-three heads from sub-adult (12-14 months) emus were used to provide a definitive description of the oropharynx and proximal oesophagus. Besides supplying baseline morphological data of veterinary importance, this study also underlines the functional importance of this region. The mandibular and maxillary nails, and serrations on the rostral mandibular tomia, provide the emu with a formidable combination of gripping, tearing and pecking power. The folded oropharyngeal floor allows distention of the dorso-ventrally flattened cavity during eating and drinking. The laryngeal mound performs both respiratory and digestive functions, whereas the distensible proximal oesophagus supports the particular feeding method employed by ratites.

Although a number of brief, fragmented descriptions have been provided on the gross morphology of the ratite tongue, very few studies have documented the histological structure of this organ. This paper presents the first definitive histological description of the emu tongue and reviews, consolidates and compares the scattered information on the histology of the ratite tongue available in the literature. Five tongues were removed from heads obtained from birds at slaughter and fixed in 10 % neutral buffered formalin. Appropriate longitudinal and transverse segments were removed, routinely processed for light microscopy, and sections examined after staining with H & E and PAS. The entire tongue (body and root) is invested by a non-keratinized stratified squamous epithelium. The supporting connective tissue of the tongue dorsum displays only large, simple branched tubular mucussecreting glands, whereas the caudal tongue body ventrum and tongue root, in addition to these glands, also exhibits small, simple tubular mucus-secreting glands. Herbst corpuscles are associated with the large, simple branched glands. Lymphoid tissue is restricted to the tongue ventrum and is particularly obvious at the junction of the ventral tongue body and frenulum where a large aggregation of diffuse lymphoid tissue, with nodular tissue proximally, was consistently observed. A structure resembling a taste bud was located in the epithelium on the caudal extremity of the tongue root of one bird. This is the first reported observation of taste buds in ratites. Forming the core of the tongue body is the cartilaginous paraglossum lying dorsal to the partially ossified rostral projection of the basihyale. The histological features of the emu tongue are generally similar to those described for the greater rhea and ostrich, except that taste buds were not identified in these species. The results would suggest that the emu tongue functions as a sensory organ, both for taste and touch (by virtue of taste receptors and Herbst corpuscles, respectively), as well as fulfilling an immunological function.

The final publication is available at http://www.springerlink.com/content/6j37487920884049/ Abstract The tongue body of Rhea americana is triangular and partially pigmented with each caudo-lateral margin displaying a round, sub-divided lingual papilla. The tongue root is a smooth, non-pigmented tract of mucosa. The tongue body is supported by the paraglossum and distal half of the rostral projection of the basihyal (RPB), and the tongue root by the proximal half of the RPB, body of the basihyal and proximal ceratobranchials. An urohyal is absent; however, peculiar to R. americana, the caudal margin of the cricoid body displays a median projection, which may represent the remnant of the urohyal incorporated into the cricoid. The laryngeal mound is less elevated, the arytenoid cartilages are smaller than in other ratites, and the caudal margin displays pharyngeal papillae that vary in shape and number. The unique morphology of the lingual skeleton and its positioning within the tongue of R. americana, the rostral insertion of the M. ceratoglossus, the absence of the urohyal (enhanced ventroflexion) and the caudal positioning and mobile attachment of the ensheathed basihyal to the paraglossum would appear to allow independent movement of the tongue body relative to the hyobranchial apparatus. Additionally, the deeply indented base and rostral oval opening in the paraglossum limits the length of cartilage present in the midline of the tongue body. This may allow the tongue the necessary flexibility for the lingual papillae to clean the choana. The cleaning action of the tongue would occur simultaneously Communicated by T. Bartolomaeus.M. Crole ( ) • J. Soley Department of Anatomy and Physiology, Faculty of Veterinary Science, University of Pretoria, Private Bag X04, Onderstepoort 0110, South Africa e-mail: martina.crole@up.ac.za with the previously described role of this organ and associated structures during feeding. Thus, the so-called reduced, ancestral tongue of R. americana may be structurally and functionally more complex than previously believed.