Histological investigation of the nictitating membrane ofElanus caeruleus
The nictitating membrane of Elanus caeruleus is divided into two
regions; the head and body. Further, the head of the membrane can be
distinguished into two parts: the plica marginalis (free margin)
externally and the leading edge internally (Fig.10 a& b), and both are
covered by stratified epithelium (Fig. 10 b). This epithelium changes
into stratified cuboidal epithelium to form the leading edge (Fig. 10
b). This stratified cuboidal epithelium has short cytoplasmic extensions
(Fig. 10 b), which decrease gradually and then disappear toward the
fornix conjunctiva bulbi (Fig. 10 c). Numerous pigmented granules are
interspersed in the connective tissue of the plica (Fig. 10 b). The body
of the nictitating membrane possesses two surfaces: the palpebral and
bulbar surfaces. Both surfaces are covered by stratified cuboidal
epithelium with an irregular apical membrane (Fig. 10 c). while This
epithelium changes into the stratified columnar type containing goblet
cells toward the fornix conjunctiva bulbi (Fig.10 d).
The high magnification of the epithelium of the bulbar surface of the
nictitating membrane of Elanus caeruleus revealed four nucleated
cell layers; the stratum basal has cells with irregular basal lamina
forming basal finger-like fine protrusions (Fig. 11 b). The apical
membrane of the superficial cells located between the folds has a short
cytoplasmic extension. Moreover, there are numerous scattered goblet
cells, which increase in the fornix conjunctiva bulbi (Fig. 11 b). The
palpebral surface is composed of six nucleated cell layers. The
superficial cells have pale cytoplasm and irregular apical membrane
(Fig. 11 a)
Ultrastructure investigation of the nictitating membrane ofElanus caeruleus
The ultrastructure of the nictitating membrane of Elanus
caeruleus revealed the flattened cells of the palpebral surface appear
loosely connected with each other by complex interdigitations of the
cell membranes. Furthermore, the cytoplasm contains many cytoplasmic
vacuoles of varying size (Fig. 12 a).
The Immature M cells observed in the bulbar surface are lighter compared
to the neighboring
enterocytes and abundant various
sizes of vacuoles in the apical cytoplasm. M cells exhibited shorter and
irregular microvilli on their apical membrane compared to the
neighboring enterocytes. In addition, goblet cell with free edge (Fig.
12 b & c) and enterocyte-like columnar cells were observed (Fig. 12 b
& c)