Author(s) :

Ghulam Murtaza, Razia Kausar, Muhammad Adil, Bushra Zaidi.

Volume/Issue :

Abstract :

This review examines the nictitating membrane, a specialized third eyelid present in various animal groups, and its relation to the plica semilunaris. It highlights the distinctive features of the nictitating membrane in birds, its sophisticated neuro-muscular mechanism, and its protective role in maintaining vision. Besides this, the study investigates the plica semilunaris of mammals and illustrates its structural complexities, including a cartilaginous base, and its role in clearing foreign particles from the eye. Microscopic analyses of both structures in birds and mammals reveal unique tissue compositions and glandular arrangements, further elucidating their functional disparities. Particularly, the examination underscores the differences in the neuro-muscular apparatus in mammals compared to birds, emphasizing the presence of two distinct mechanisms controlled by different cranial nerves. The study proposes the use of the terms "plica intercipiens" and "cartilage intercipiens" to accurately describe these structures. Additionally, it emphasizes the necessity of exploring the ontogeny of mammalian structures to understand their morphological distinctions from the nictitating membrane fully. Overall, this review emphasizes the critical need for a comprehensive understanding of the protective eye mechanisms across different animal species, contributing to our knowledge of their evolutionary adaptations and functional significance.

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18