Nervous and Sensory Functions
The brain of reptiles is similar to the brains of other verte-
brates. The cerebral hemispheres are somewhat larger than
those of amphibians. This increased size is associated with an
improved sense of smell. The optic lobes and the cerebellum
are also enlarged, which reflects increased reliance on vision
and more refined coordination of muscle functions.
The complexity of reptilian sensory systems is evi-
denced by a chameleon’s method of feeding. Its protruding
eyes swivel independently, and each has a different field
of view. Initially, the brain keeps both images separate, but
when an insect is spotted, both eyes converge on the prey.
Binocular vision then provides the depth perception for
determining whether or not the insect is within the range of
the chameleon’s tongue (see figure 20.12).
Vision is the dominant sense in most reptiles, and their
eyes are similar to those of amphibians (see figure 19.15).
Snakes focus on nearby objects by moving the lens forward.
Contraction of the iris places pressure on the gel-like vitreous
body in the posterior region of the eye, and displacement
of this gel pushes the lens forward. All other reptiles focus
on nearby objects when the normally elliptical lens is made
more spherical, as a result of ciliary muscles pressing the cili-
ary body against the lens. Reptiles have a greater number of
cones than do amphibians and probably have well-developed
color vision.
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