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

2.1 Introduction
This introduction will summarize the relevant background information of spectacle anatomy and
physiology described in Chapter 1 so as to provide a context for the research presented here such that
this chapter can be read as a standalone account.
The spectacle of snakes and geckos is a layer of transparent integument that overlays the eye,
isolating it from the external environment. Arising from the fusion of embryonic tissues that would
otherwise form eyelids (Schwartz-Karsten 1933; Neher 1935; Bellairs & Boyd 1947), the spectacle’s
anatomy is homologous with that of the skin in having a stratum corneum (the spectacle scale), a
complex epidermis and a dermis, but differs in possessing a subdermal conjunctival layer similar to
that of eyelids (Ficalbi 1888b; Walls 1942).
Unlike either the skin or most eyelids however, the spectacle is optically transparent, ideally
suited to vision but for one characteristic that it shares with the rest of the integument: its vascularity
(Figure 2-1).
Figure 2-1. Photographs of the eye of a coachwhip snake, Masticophis flagellum, during the
renewal phase of the integument (A) and with retro- and cross-illumination (B), showing the dorso-
ventrally arrayed spectacle blood vessels. (photos by K. van Doorn)!
A B
The presence of blood vessels in the spectacle dermis was first demonstrated by Quekett
(1852). The vascular supply to and anatomical layout of the snakes’ spectacle blood vessels was later
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