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

The two layers he described in the snake spectacle are now known to consist of different types
of keratin, just as are other scales in the snake integument (Maderson 1985). While the complex
layering of the keratins have been studied in snakes (Alibardi and Toni 2005a), geckos (Alibardi and
Toni 2005b) and other squamates (Alibardi and Toni 2006), no work has been published on the
specifics of the spectacle scale. Chapter 4 will discuss the keratin composition of the squamate
integument and spectacle scale in greater detail.
Although the spectacle shares the same overall anatomical structure as the skin, it is markedly
more thin (Rochon-Duvigneaud 1943; Duke-Elder 1958). Due to tissue distortion that occurs during
most histological preparations, the exact thickness of the whole spectacle had not been accurately
ascertained until the development of modern ocular imaging techniques. Making use of
ultrasonography, Hollingsworth et al. (2007) found spectacle thickness to vary between species. Its
thickness is comparable between corn snakes (Elaphe guttata), California kingsnakes (Lampropeltis
getula californiae) and ball pythons (Python regius), varying from 184 to 190 µm in these species, but
is thicker in the gopher snake (Pituophis melanoleucus) at 220 µm. This variation may be largely due
to the thicker spectacle scale of P. melanoleucus (see Chapter 3), indicating that the epidermis, dermis
and conjunctiva together are of comparable thicknesses in all these species.
The surface of all scales of the snake integument bear microscopic ultrastructural features,
such as micropits and interdigitating plates with varied stepping heights between the plates, somewhat
similar in appearance to shingles on a roof (Hoge and Souza Santos 1953; Chiasson and Lowe 1989).
The micropits have been suggested to serve as channels for sebaceous secretions (Chiasson et al.
1989). The morphology, patterning and density of these structures differ in different scales. Campbell
et al. (1999) have shown that the spectacle scale of a python has larger plates with lower stepping
heights than other scales, resulting in an overall smoother surface, which would improve transparency
of the scale by reducing light scatter.
A curious feature of the spectacle that it shares with the rest of the integument is its vascularity.
Other than the neural retinas of mammals and snakes and the corneas of Florida manatees (Harper et
al. 2005), no other vertebrate is known to have blood vessels within the optically transmissive portions
8