Ultrastructure investigation of the upper and lower eyelids ofElanus caeruleus
Transmission electron microscopical study of the eyelids skin ofElanus caeruleus revealed melanocytes of spherical to oval shape and are located mainly in the basal layer of the epidermis. Moreover, they have an oval nucleus with clumps of condensed chromatin. The cytoplasm of the melanocytes has numerous melanin granules and the cytoplasmic processes of melanocytes were also clearly observed (Fig.7a &b).
The keratinocytes in stratum spinosum are characterized by a large rounded euchromatic nucleus. They are tightly connected by numerous tonofilaments (keratin filaments) crossing the intercellular spaces and extending into junctions between the cells (Fig.7a &b).
The Langerhans cells are non-pigmented, and found in the basal and spinosum layers. They are characterized by pale cytoplasm, deeply indented and heterochromatic nucleus and the presence of specific Langerhans granules. In addition, free ribosomes, mitochondria and some membranous vesicles of variable size (Fig. 7a & c). The stratum corneum constitutes the superficial layer, which lacks nuclei and is formed of wavy keratin (fig .7a)
The ultrastructure of the conjunctival epithelium of the lower eyelid revealed irregular cytoplasmic extensions emerging from the cell surface. Moreover, the epithelial cell contains a round and euchromatic nucleus and is enriched with smooth endoplasmic reticulum, few mitochondria and numerous membranous vesicles of varying size (Fig. 7d).
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Morphological investigation of the nictitating membrane of Elanus caeruleus
The nictitating membrane of Elanus caeruleus is a white opaque membrane, have palpebral and bulbar surfaces (Fig.8a). Anatomical and scanning electron microscopy of the nictitating membrane revealed several folds on their surfaces (Figs.8 a& c). the irregular surface of the free margin has a few shallow pores (Fig.8b). Furthermore, moderate-density cytoplasmic extension appeared in the apical cells on the bulbar surface (Fig. 8), which disappears towards the fornix conjunctiva bulbi and the intercellular border of the bulbar surface (Fig.8e). Many pores scattered between the folds of the bulbar surface (Fig.8e).
The laboratory observation of the movement of the eyelids ofElanus caeruleus showed that the nictitating membrane slips rapidly in an oblique direction from the dorsonasal angle toward the ventrotemporal direction (Fig.9).