Scanning electron microscopic observations of the digestive canal of the Great Bustard (Otis tarda)

This study focussed on the microstructure of the digestive canal of the Great Bustard (Otis tarda). Under scanning electron microscopy (SEM), different morphological plicae (rounded protrusions about 10 mu m in height) were observed at different locations along the inner surface of the oesophagus. Concentrated microvilli can be seen on the surface of the protrusions in high-power fields. There are papillae in the mucosal fold on the inner surface of the glandular stomach, with openings of about 250 mu m in diameter. In high-power fields, the tops of rod cells could be seen in somewhat circular forms with microvilli on them. Inside the muscular stomach, the scraggly- or wavy-formed surface of the cuticle layer could be seen. Stripping off the cuticle layer, at the tops of mucosal folds row- or rope-like forms could be seen. The mucosa of the small intestine is thrown into ridges running longitudinally in a zigzag pattern along the intestine, rather than the finger-like intestinal villi observed in mammals. There are villi on the inner surface of the caecum with impressions on their domes (the troughs between which have diameters of about 200 mu m). Villi on the inner surface of the rectum are even thicker, ranging from 200-500 mu m in diameter, and could be seen on the inner surface of the caecum and rectum. Outlines of cell domes are clearer on the inner surface of the caecum than those on the rectum. Studies on the fine structures of the inner surface of the Great Bustard digestive canal will enrich the knowledge of the comparative histology of birds, and provide a reference for raising bustards, as well as preventing and curing its diseases.