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

1.1 Anatomy of the spectacle
The simplest description of a spectacle is that of transparent integument that overlays the eye. Walls
(1942) recognized three main types of spectacle, which he referred to as primary, secondary, and
tertiary types, differentiated from one another by their developmental origin and anatomical
relationship with the eye. Primary spectacles, found in lampreys, are perhaps the most primitive form,
composed of skin overlaying the eye, under which the eye is apposed directly against the dermis but
remains unattached so it may move freely. Secondary spectacles are found in some fishes and differ
from the primary type in that the cornea is fused with the dermis, but with sufficient loose tissue
around the eye to still allow for rotation. Tertiary spectacles, found in reptiles, amphibians and again in
some fishes, appear to be the most evolved form in which eyelids develop a transparent component and
are manifested as “windowed” eyelids or altogether fuse over the eye. While similar to the primary
type, the tertiary form differs in that the cornea of the eye is not apposed directly against the
spectacle’s dermis, but rather the posterior of the spectacle is lined with conjunctival epithelium,
continuous with that of the eye, which encloses a fluid filled pocket between the spectacle and cornea,
allowing the eye to rotate freely, lubricated by a fluid analogous to the tear layer of lidded vertebrates.
Because only the tertiary spectacle is found in reptiles, this discussion will focus entirely on its
characteristics. Historically, the nomenclature of the spectacle has been as varied as the linguistic
heritages of the anatomists who have studied it and their beliefs of its origin: paupière, brille, lunette,
apparecchio palpebrale... Modern English accounts have settled on “spectacle” and its German
translation “brille” (‘brill-uh’), and though this review will primarily make use of “spectacle,”
historical precedent necessitates certain brillar references.
1.1.1 The Spectacles of Snakes
There was little agreement among early anatomists and naturalists regarding the nature of the
spectacle’s relationship with the eye. While it was certainly understood by anyone who came across a
snake’s shed skin that its eye was covered by a transparent scale, as attested by Rochon-Duvigneaud’s
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