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

4.1 Introduction
The reptilian spectacle is a layer of specialized integument that overlays the eyes of snakes, most
geckos, and a varied array of other squamates (Walls 1942). A hard, optically transparent scale forms
its outer surface. This scale is of a highly specialized nature, as few other reptilian scales achieves the
same degree of optical transparency (see Chapter 3).
Ficalbi (1888b) established that the snake spectacle scale consists of two main layers, an
internal and an outer stratum corneum, separated by a clear layer (see Figure 1.2 in Chapter 1). Given
that the spectacle scale likely has the same anatomical layering as the rest of the reptile integument, the
two main layers should correspond with the alpha (inner) and beta (outer) layers, distinguished by the
predominant type of keratin of which they are composed, while the clear layer is likely to be an
artifactual separation of the mesos layer that frequently occurs during histological procedures. Little
research has been done on the fine anatomy of the spectacle stratum corneum specifically, but if it is
assumed to be layered similarly to the integument, an intact spectacle would contain 4 layers
(Maderson 1964; Landmann 1986; see Figure 4-1, next page): 1) an oberhautchen layer on the surface,
which consists of surface ultrastructural features; 2) a hard beta layer beneath this, often thick in
snakes, called as such because it is primarily composed of beta(ß) keratins; 3) the mesos layer,
consisting of thin repeating layers of keratin and lipid; and (4) an alpha layer, referred to as such
because it is primarily (but not exclusively) composed of α keratin (Maderson 1965; Maderson 1966;
Alexander & Parakkal 1969; Maderson 1998; Alibardi 2005). Two additional α keratin layers form
during the renewal phase: (5) the lacunar layer and (6) the clear layer. These are thought to be involved
in shedding the old, outer stratum corneum and remain attached to the shed skin. Ficalbi briefly
mentioned that the gecko spectacle is similar to a snake’s other than perhaps a thinner stratum
corneum. No other research has been published on the fine histology of the gecko spectacle, so the
spectacle scale’s layered structure is not known. Between scales is the hinge region which contains less
or no ß keratin and is therefore more elastic, allowing for an unrestrained range of motion and
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