Chapter 1, The Reptilian Spectacle - UWSpace - University of ...

Gymnophthalmus (spectacled tegus) and Micrablepharus (Walls 1942; Greer 1980; Greer 1983). This
list is by no means exhaustive but hopefully conveys the diversity of eyelid modifications in reptiles.
The anatomy of windowed eyelids and spectacles in these species has been little studied
beyond their superficial morphology. Mead (1976) reported finding blood vessels in the spectacle of a
xantusiid night lizard but did not describe the layout of the meshwork. It is thus still not known if and
how the eyelid windows and spectacles in these species are vascularized. Cross-sections of eyelid
windows have been presented as diagrams (Angel and Rochon-Duvigneaud 1941; Bellairs and Boyd
1947), but no high-resolution studies of their histology have been published. The pressing question
remains of whether eyelid windows are vascularized and whether the eyelid muscles and glands are
arrayed in such a way to minimize their presence in the transparent portion. Curiously, Ablepharus and
Ophisops, both fully spectacled, retain the depressor palpebralis inferioris muscle which inserts into
the spectacle’s inferior border (Underwood 1970).
1.2 Spectacle Development
The development of the spectacle has been described for snakes and geckos (Schwartz-Karsten 1933;
Neher 1935; Bellairs and Boyd 1947; Bellairs 1948; Boughner et al. 2007). It generally consists of the
proliferation over the developing eye of mesenchymal tissues until they meet and fuse, becoming
transparent and void of all glands and typically of muscles otherwise found in eyelids (Underwood
1970). The tissues may take the form of eyelids, with the margin of the lower “lid” gradually
progressing upward until it meets the upper lid and fuses, while in others, the extraocular tissues
migrate inward from all around the circumference of the eye, gradually shrinking the aperture over the
eye until it vanishes. While the former description of fusing eyelids may have the appearance of a
truncated version of mammalian eyelid development, in which developing integumentary tissues fuse
over the eye and then separate again as distinct eyelids (Addison and How 1921; Pearson 1980;
Findlater et al. 1993), it should be emphasized that eyelid development in birds and reptiles does not
appear to involve fusion at any stage (Hamburger and Hamilton 1951; Hays and Lecroy 1971; Billy
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