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

Figure 1-6. Photograph of the eye of a
coachwhip snake, Masticophis flagellum,
during the renewal phase. The vertically
oriented blood vessels of the spectacle are
visible around the pupil. The clouding of the eye
is characteristic of the renewal phase of the
integument. (photo by K. van Doorn)
Mead (1976) added to this work by showing the layout of spectacle blood vessels of crotaline
vipers to have a radial arrangement as in boids and pythons and that elapid snakes (specifically a
siamese cobra, Naja naja kaouthia) have a vertically oriented meshwork as in colubrids but with a
reduction in vessel size at the centre of the spectacle and a much greater degree of complex
anastomoses away from the optic axis. Although Mead made no mention of the adaptive significance
of this latter point, it is again a compelling thought that this arrangement is such that visual disturbance
due to the vessels might thus be minimized on the animals’ optic axis, an anatomically distinct but
functionally similar adaptation to that found in A. nasuta. Although Mead also reported examining the
spectacle vasculature of a xenopeltid snake, but did not include a description or images of its
organization. On the vascular flow through the spectacle vessels, Mead (1976) reported only that “the
vessels [ ] fill without any obvious directional priority in the anesthetized animal.”
Lüdicke’s studies of spectacle vasculature also included the measurement of blood vessel
diameters. In Python reticulatus, the diameters of the proximal afferent vessels are approximately 30
µm, large enough to pass several erythrocytes abreast. No values were given for the smaller branches,
but it is evident from photographs of the injected vessels that their diameters decreased toward the
center of the spectacle at the optic axis -- again hinting at an adaptation to minimize visual disturbance.
In the case of A. nasuta, no values were given for the vessels’ diameters, but a photograph of the
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