Histology of the trachea and lung of Siphonops annulatus (Amphibia, Gymnophiona).

The structure of the trachea and lung of Siphonops annulatus was studied in ten specimens of routinely fed animals. The trachea is constituted mainly by incomplete cartilage rings lined by a respiratory epithelium (ciliated and mucous cells) with variable morphology according to the region observed. A rich vascularization of this organ suggests its participation in blood-air gas exchange. The right lung in this species is developed and the left one is atrophied. This organ is constituted mainly by longitudinal septa formed by connective tissue, smooth muscle cells and blood capillaries. These structures are covered by pneumocytes of one type only, which present cytoplasmic particles that have been related with surfactant activity described in the lung of Gymnophiona.