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).