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

1.1.2 The Spectacles of Scolecophidian Snakes
Figure 1-9. Early diagram of the typhlopid eye and its
relationship with the spectacle. The spectacle dermis (d) is
noticeably thinned compared to surrounding areas. cj. s. conjunctival
sac; b. brille (spectacle); F. cj. fornix conjunctiva; cor. choroid/iris; o.s.
outer stratum corneum; l. lens; r. retina. Reproduced from Eigenmann
1909.
All the descriptions thus far have been on alethinophidian snakes, that largest superfamily which
includes all but the most basal snakes, the Scolecophidia or blind and thread snakes. These share
similarities of the spectacle anatomy with alethinophidians (Eigenmann 1909; Foureaux et al. 2009),
including the thinning of the tissues immediately overlaying the eye, but differ in the size of the scale
covering the eye. In alethinophidians, the spectacle scale is sufficiently broad to cover the cornea of the
eye and little beyond. In scolecophidians, however, the scale overlaying the eye extends well beyond
its margins, in some cases covering a significant portion of the head. In these species, the scale is more
properly referred to as the ocular scale, and in those where it extends to the mouth, it may be called the
oculolabial scale. In all species, usage of the term “spectacle” should be restricted to the specialized
integument immediately overlaying the eye.
A recently discovered species of leptotyphlopid, Leptotyphlops macrops (“larged eyed thread
snake”), is distinguished in having much larger eyes than all other scolecophidians (Broadley and
Wallach 1996). To accommodate the size of the eyes, a dome is formed in the ocular scale. The eyes of
this unique snake may represent a transitional form in the evolution of snake eyes from the reduced
scolecophidian form to the more sophisticated alethinophidian eye.
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