Macro- And Microanatomical Study of the Orbital Glands of the Common Moorhen "Gallinula Chloropus"

Abstract

Numerous and variable studies have been done about the avian orbital glands. However, more comparative investigations including several species need more attention. The current study intends to investigate the relationship between the morphological, histological, and histochemical features of the orbital glands of the common moorhen (Gallinula chloropus), and their protective function for the eye. There are two lacrimal glands in the common moorhen, which differ in size, shape, location, and position of their openings. The dorsal lacrimal gland appears as a bilobed cylindrical gland with dorsoventrally compressive tissues situated within the fossa in the dorsal orbital rim, and unites anteriorly beneath the lacrimal bone to form its draining duct. A small lateral lacrimal gland is located on the posterior pole of the eyeball. The Harderian gland appears voluminous with an irregular, multi-lobed shape. Histologically, the orbital glands are composed of compound tubulo-alveolar type, with each acini lined with cuboidal cells with large spherical nuclei and covered with a pigmented capsule. These glands reveal various positive reactions with periodic acids Schiff's reagent and Alcian blue (pH = 2.5). The present study concluded that the common moorhen possesses different types of orbital glands: two lacrimal glands and a voluminous Harderian gland. The current study suggested that the orbital glands change their features in this bird that catches their food from underwater to adjust the water-visual refraction; furthermore, according to their acidic secretions, this gland may allow the protection of the eye against any water pollution.