Visual System in a Lizard 
87 
Ventral Thalamus 
The cytoarchitectonic map of J. Cruce 
(1974) was used as a reference on which to 
place the results of our experimental study. 
It was found, however, that the pattern of 
labeling of retinal terminals did not com- 
pletely correspond with the cytoarchitectonic 
pattern as described from normal cell stained 
material. In addition to the prominent ventral 
lateral geniculate nucleus located on the 
medial edge of the optic tract, two small 
areas ventral to that nucleus had dense 
terminal labeling and probably represent 
subdivisions of that nucleus ; these same 
subdivisions were identified in the Tegu 
lizard by Ebbesson, Jane, and Schroeder 
(1972) as recipients of contralateral projec- 
tions from the retina in the Tegu lizard. 
Based on an autoradiographic study in the 
loggerhead sea turtle (Caretta caretta), Bass 
and Northcutt (1975) were able to distin- 
guish dorsal and ventral components of the 
GLV, both of which receive retinal terminals. 
In the present results, the retina was seen 
to project bilaterally to the GLV, with the 
ipsilateral GLV receiving a less dense pro- 
jection. Ebbesson (1970), in his study of the 
Tegu lizard mentions only a contralateral 
projection from the retina to GLV. Butler 
and Northcutt (1971) saw only one animal 
in which an ipsilateral projection was evi- 
dent. On the other hand, bilateral projections 
to the GLV from the retina were found in 
Lacerta (Armstrong, 1950), Xantusia (But- 
ler, 1974), and Gekko (Northcutt and Butler, 
1974a). 
Pretectum 
The pretectum is an area of the brain 
which shows a great deal of variation in both 
form and nomenclature from species to spe- 
cies. In all species studied some of the pre- 
tectal nuclei have been observed to be recip- 
ients of retinal ganglion cell axons. Ebbesson 
(1970), in his study of retinal projections in 
the Tegu lizard, indicated that nucleus post- 
erodorsalis of the pretectum receives a bi- 
lateral retinal projection; our results are in 
agreement. According to Ebbesson (1970), 
nucleus geniculatus pretectalis and nucleus 
lentiformis mesencephali receive only con- 
tralateral fibers from the retina, whereas 
we found these projections to be bilateral. In 
addition, we found a contralateral projection 
to nucleus pretectalis and to the dorsal edge 
of nucleus pretectalis dorsalis ; Ebbesson 
(1970) does not mention these projections. 
One explanation for the discrepancy be- 
tween our findings and those of Ebbesson 
in the same species (Tupinambis nigro- 
punctatus), may be the different techniques 
that were employed. Ebbesson (1970) used 
anterograde degeneration, and we used 
anterograde transport. Even within the same 
species, we have seen what appears to be 
anomalous degeneration which can cause 
staining of pathways which were not ex- 
perimentally lesioned (Cruce and Cruce, 
1975). A small number of degenerating fibers 
might not be distinguishable from normal 
stained fibers whereas the silver grains of 
the labeled protein molecules are more easily 
distinguished above background levels of 
labeling, especially using dark-field illumina- 
tion. 
Contralateral retinal fibers invariably ter- 
minate in nucleus geniculatus pretectalis and 
nucleus lentiformis mesencephali. As in the 
present study, there are bilateral projections 
in Gekko and Xantusia (Northcutt and But- 
ler, 1974a; Butler, 1974). Armstrong (1950) 
did not find any retinal fibers terminating 
in the nucleus posterodorsalis of Lacerta, 
whereas other authors did. The nucleus pre- 
tectalis as shown here has not been identified 
by any authors except Butler and Northcutt 
(1971) who, in agreement with our observa- 
tions in the Tegu lizard, found that it re- 
ceives contralateral retinal fibers. 
Tectum 
In all reptiles the contralateral optic tec- 
tum receives an input from the retina. Only 
two other reports in lizards (Butler 1974; 
Northcutt and Butler, 1974a) and one in a 
snake (Reperant, 1973) contain descriptions 
