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

specialized mechanoreceptor tubercles on colubrid spectacles, in contrast with scales elsewhere on
their head. Of course this demonstrates nothing about what receptor types spectacles do possess, with
the possible exception of the leptotyphlopid. It is likely that the spectacle innervation is at least partly
sensory in function, given that nerve endings extend to the epidermis, but autonomic innervation to the
spectacle vasculature may also be present as it is with all cutaneous vasculature (Baker et al. 1972;
Rowell 1977), particularly in light of the spectacle vascular dynamics presented in Chapter 2.
Figure1-7. Early illustration of the spectacle nerves of
the colubrid snake Natrix tessellata. The nerves are seen
penetrating radially into the spectacle from all around the
circumference with complex anastomoses occurring in the
branches. From Crevatin 1904.
An interesting aside about the spectacle nerves is that, as Crevatin (1904) observed and
remarked upon with enthusiasm, their layout is similar to that of corneal nerves in other species.
Human corneal nerves, for example, penetrate into the corneal stroma from around the corneolimbal
circumference with only the exception of the dorsalmost and ventralmost areas. Within the stroma,
they extend fine nerve endings toward the epithelium (Müller et al. 1997). Morphologically, the
individual neurons of the spectacle are similar as well to those of human corneal nerves as observed
with in vivo confocal microscopy (Figure 1-8, next page) where mitochondrial aggregations in the
form of beads can be observed along the axons.
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