Behavior and Neurology of Lizarde 
N. Greenberg and P. D. MacLean, eds. 
NIMH, 1978. 
Analysis of the Visual System in a Lizard, 
Tupinambis Nigropunctatus 
Judith A. F. Cruce* 
Department of Anatomy 
Johns Hopkins University School of Medicine 
and 
William L. R. Cruce* 
Department of Anatomy 
Howard University College of Medicine 
and 
Department of Neurobiology 
Armed Forces Radiobiology Research Institute 
SUMMARY. Retinal projections were studied in the Tegu lizard, Tupinambis nigropunctatus, 
by employing the method of autoradiographic tracing of anterograde axonal transport. In agree- 
ment with the general pattern of vertebrate visual projections as outlined by Ebbesson (1970), 
retinal fibers terminate in six areas of the brain of the Tegu lizard, as follows : dorsal thalamus, 
ventral thalamus, pretectum, tectum, hypothalamus, and nucleus of the basal optic tract. Most of 
these areas receive fibers from both the contrlateral and ipsilateral eye with the exception of 
the hypothalamus and nucleus of the basal optic tract, which receive only contralateral fibers. 
INTRODUCTION 
The visual system plays an important role 
in the behavior of all vertebrates. Through 
the retina of the eye, visual information 
reaches many parts of the nervous system 
where the information can be analyzed, in- 
tegrated, and acted upon. Visual information 
is received by the retinal ganglion cells and 
transmitted via axons traveling first as the 
optic nerve and then as the optic tract to the 
brain. In the present study, projections from 
retinal ganglion cells to the brain will be 
described in one species of lizard, the Tegu 
lizard, Tupinambis nigropunctatus. The Tegu 
lizard possesses large eyes, is diurnal, and, 
based on our informal observations of these 
animals in the laboratory, it appears to be 
very attentive to visual stimuli. 
In recent years experimental analysis of 
the visual system has been made in a variety 
* Present Address; Department of Anatomy, North- 
eastern Ohio Univ. Coll. Med., Rootstown, Ohio 44272 
of different reptiles, including several species 
of lizards: Lacerta vivipara (Armstrong, 
1950), Xantusia vigilis (Butler, 1974), 
Iguana iguana and Anolis carolinensis (But- 
ler and Northcutt, 1971), Tupinambis nigro- 
punctatus (Ebbesson, 1970; Cruce and Cruce, 
1975), Gekko gecko (Northcutt and Butler, 
1974a). 
The retinofugal fiber system of lizards fol- 
lows the general pattern for all vertebrates 
as outlined by Ebbesson (1970). The axons 
of retinal ganglion cells terminate in six 
areas of the brain as follows: dorsal thala- 
mus, ventral thalamus, pretectum, tectum, 
hypothalamus, and nucleus of the accessory 
or basal optic tract. Some of these projections 
are contralateral only, while others are both 
contralateral and ipsilateral. 
Bilateral retinal projections appear to be 
related to binocular vision and may allow for 
more complex analyses of visual information 
in those animals which possess them than in 
those animals which do not. Among the rep- 
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