The Role of the Ocular Lids of the Black-Winged Kite, Elanus caeruleus, in the Immune Protection of the EyeNahed Ahmed Shawki1, Abdelraheim H Attaai2, Amany Mohamed Abdel- Mageed1, Fatma Abdel- Regal Mahmoud11 Assiut University, Faculty of Science. Zoology Department, Assiut, Egypt.2 Department of Anatomy and Embryology, Faculty of Veterinary Medicine, Assiut University, Assiut, Assiut 71526, Egypt.2 Department of Anatomy and Histology, School of Veterinary Medicine, Badr University in Assiut, Assiut 11829, Egypt; [email protected]

The present study aimed to describe the anatomical, scanning electron microscopic, and histological features of the ocular eyelids and muscles of the Egyptian agama, Trapelus mutabilis. The eye of the Egyptian agama is characterized by mobile upper and lower eyelids and a small, immobile, nictitating membrane. The upper eyelid appears shorter than the lower one, and the head skin above the upper eyelid extends laterally to form a superior extension. The scales of the eyelids are arranged in the same order and are equipped with micro-ornamentation and sense organs at their tips. In contrast, the histological structure of the upper eyelid is similar to that of the lower eyelid. The external surface of both eyelids is composed of keratinized stratified squamous epithelium of 2-4 cell layers, while cuboidal stratified epithelium lines their internal surface. Both eyelids contain iridophores and melanophores. The immobile nictitating membrane (third eyelid) appears as a small protrusion with a concave surface that connects with the lacrimal gland posteriorly at the anterior canthus of the eye. Its external surface is covered with stratified squamous epithelium, while its internal surface is lined by one or two layers with rounded nuclei attached to the conjunctival epithelium. Video recordings of eye movement in the laboratory revealed that the movement of the eyelid is synchronized with the eyeball movements, allowing all eye movements to be observed. The placement of the eye inside the skull, its protection by two eyelids equipped with hard scales and sensory organs, and the presence of a superior extension of broad scales acting as an umbrella for the eyes, in addition to the presence of two types of pigment cells, enhance eye protection against ultraviolet rays. All these characteristics are well-suited for the remote desert environment in which the agama lives.

The aim of the study was to describe the morphological features and microstructure of the upper, lower, and third eyelids of black-winged kite, Elanus caeruleus, as well as characterize the organized lymphoid follicles and lymphocytes in the eyelid’s mucosa, and to illustrate the importance of the eye adnexa in the eye’s immune protection. The black-winged kite has large forward-facing eyes placed under a bony shelf (lacrimal process) that shaded them. Both eyelids have thick and pigmented edges and bear two rows of long and finely modified filoplume feathers that increase at the anterior canthus. It was found that the lower eyelid appears longer and thinner than the upper one, as well as having sparse feathers on the skin surface of the lower eyelid but lack on the upper. The third eyelid is a white opaque membrane moving obliquely over the cornea surface. The melanocytes appear in the stratum basal of upper and lower eyelids and the Langerhans cells were observed within the layers of stratum spinosum, near the feather follicle and around the blood vessel. Aggregations of lymphatic cells were present under the conjunctival epithelium within the stroma of the lower eyelid (in the orbital zone near the tarsal plate), while absent in the upper eyelid and nictitating membrane. The present study revealed that many high endothelial venues (HEV) are distributed along the lower eyelid and increase in the palpebral marginalis, while in the upper eyelid, it is restricted in the marginal region. The density of goblet cells on the conjunctiva surface of the upper eyelid and the nictitating membrane is higher than that of the lower eyelid. The leading edge and bulbi surface of the third eyelid reveal the irregular surface of the apical cell, with many cilia having variable amounts of secretory vesicles as shown by TEM.