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

Figure 1-5. Illustration of the spectacle vasculature
in Hierophis viridiflavus. Vessels enter from around
the circumference of the spectacle, showing complex
anastomoses in the periphery and largely dorso-
ventral orientation at the center. Reproduced from
Ficalbi 1888b.
The vascular anatomy of the spectacle was further explored by Manfred Lüdicke who mapped
out the meshwork of blood vessels in several species of snake from several families (Lüdicke 1940,
1969, 1973, 1977; Lüdicke and Kaiser 1975). Lüdicke demonstrated that the arrangement of spectacle
vessels varies between families. For example, those of colubrid snakes exhibit a predominantly dorso-
ventral (i.e. ventral) arrangement with few anatomoses in the center (eg. Figures 1-5 and 1-6, next
page), whereas those of boids, pythonids, acrochordids and aniilids are radially arranged with varying
degrees of organization and anastomoses. The meshwork of Gekko gecko has a similar radial
organization with entry of the vessels from around the circumference. Curiously and significantly,
Lüdicke (1969) also found in the green vine snake (Ahaetulla nasuta, Colubridae), one of few snake
species known to have foveas, that the distribution of vessels is such that the nasal region of the
spectacle, which serves the temporally-located foveas and the binocular field, has a lower density of
vessels than elsewhere in the spectacle. This suggests an adaptation specifically to minimize loss of
visual clarity due to the vessels, a rather compelling theory given the highly visual nature of this
species and one that will be further discussed later.
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