Morphological investigation of the upper and lower eyelids ofElanus caeruleus
The black-winged kite, Elanus caeruleus has large forward-facing eyes placed under a bony shelf (lacrimal process) that shades them (Fig.1a). The skin covering the lacrimal process carries regular rows of feathers, like a brow, which appears as a canopy to cover the upper eyelid (Fig.1 b). This bird has un-drooping eyelids, and the lower eyelid appears more extensive and larger than the upper eyelid (Fig.1 b).
The palpebral margin of each eyelid is pigmented at variable degrees and puckered into bumps that increase toward the anterior canthus (Fig.1d). Near the margin of each eyelid, there are two rows of long and finely modified filoplume feathers as eyelashes (Fig.1c). Meanwhile, on the lower eyelid skin, filoplume feathers spar, while no feathers appear on the upper eyelid. Furthermore, a collection of copious plumage exists next to the anterior canthus of the eye (Fig.1b).,
Scanning electron microscopy investigation of the upper and lower eyelids of the Elanus caeruleus revealed the presence of heavy detached keratin and modified filoplume feathers at the ridge of the palpebral margin of each lid (Fig.2 a& b). The detached keratin disappeared at the mucocutaneous junction (MCJ) (Fig.3a), and the intercellular borders are clearly observed, as well as many scattered pores appearing on the conjunctival surface (Fig.3 b& c). In the lower eyelid, these pores are restricted \soutin to the tarsal region, and increase in size and density in its orbital region (Fig.3d). Furthermore, the microfold cells (M cell) were noticed on the surface of the two eyelids (Fig.3c) and Langerhans cells were observed underlying the basal lamina protruding their dendrites and connected with the collagen fibers (Fig.2c). Moreover, macrophage cell with filamentary pseudopods in between the collagen bundles (Fig.2d).