Anatomical and scanning electron microscopic investigations of
the eyelids of Egyptian agama
The eye of the Egyptian agama, Trapelus mutabilis , has three
eyelids: mobile upper and lower eyelids and a small, immobile
nictitating membrane. The upper eyelid is shorter than the lower eyelid.
The skin of the head above the upper eyelid extends laterally to form a
superior extension. This extension bears large, plate-like scales that
contain skin sense organs at their terminal points (Figs. 1a, b, and c).
Highly variable polygonal scales are observed on the external surface of
both eyelids, with approximately ten scales at the edges of the upper
and lower eyelids, clearly observed by SEM (Figs. 1 and 2). The
orientation of scales on the upper eyelid is similar to that on the
lower eyelid; these scales are arranged in an imbricate order, and their
surface features micro-ornamentation and Oberhäutchen with
honeycomb-like structures. These honeycomb-like structures consist of
numerous tiny honeycombs. Additionally, it was observed that the tips of
these scales possess skin sense organs (Figs. 1d and 2b)\RL.
The anatomical investigation of the nictitating membrane of T.
mutabilis revealed it to be a concave and non-mobile membrane. It is
reduced and appears as a small projection connecting with the lacrimal
gland posteriorly in the anterior canthus of the eye (Fig. 5a). SEM
investigation of the nictitating membrane revealed that its surface has
many folds marked by crypt-like structures (Fig. 5b).