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

1.1.4 The Spectacles of Amphisbaenids
Figure 1-11. Early generalized diagram of the
amphisbaenid eye and its relationship with the spectacle.
c. outer covering of the eye; con. cav. conjunctival cavity; vit.
vitreous humour; scl and chr. sclera and choroid; 1-10. layers
of the retina. The dermis (unlabeled) remains thick in this
species. Reproduced from Eigenmann 1909.
Like scolecophidian snakes, amphisbaenids are small, burrowing squamates with reduced eyes. And
rather than having a spectacle scale, theirs is an ocular scale that extends beyond the margins of the
eye, streamlining the head for burrowing, although in some the spectacle immediately overlaying the
eye may protrude convexly outward (Gans 1978). Their spectacles are composed of all the same
integumentary layers as other spectacled squamates: a stratum corneum, 2-layered epidermis, dermis
and conjunctiva (Foureaux et al. 2009). Unlike other spectacled reptiles, the amphisbaenid spectacle is
not always thinner than the surrounding integument and it may also be pigmented. The thickness and
degree of pigmentation of the spectacle seems to vary between species, being thinner in some than the
surrounding integument (eg. Trogonophis weigmanni, Amphisbaena alba, Amphisbaena mertensi, and
Leposternon infraorbitale), of the same thickness and degree of pigmentation as the integument in
others (eg. Amphisbaena strauchi, and Amphisbaena darwinii), or massively thickened and pigmented
as in Amphisbaena fuliginosa (Fischer 1899; Bellairs and Boyd 1947; Gans 1978; Foureaux et al.
2009). These reports seem to indicate that thickness of the spectacle and its degree of pigmentation are
positively correlated, suggesting that the emphasis placed on vision varies significantly among these
fossorial squamates.
In those amphisbaenids with thinned spectacles, the thinning was shown by Foureaux et al.
(2009) to be achieved by thinning each integumentary layer individually, as in other spectacled
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