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Cruce & Cruce 
of the presence of ipsilateral retinotectal 
fibers such as we have seen in our present 
study of the Tegu lizard. In the Tegu lizard 
these terminals form a thin band in layer 9 
and are limited to the rostral part of the 
tectum. The results of the other three studies 
mentioned were based on the degeneration 
observed after unilateral enucleation. In 
Gekko (Northcutt and Butler, 1974a) de- 
generating fibers were seen in layers 8-9 of 
the ipsilateral tectum, while in Xantusia 
(Butler, 1974) layers 8-14 in the rostral half 
of the tectum appear to be involved. In 
Vipera, Reperant (1973) saw scattered de- 
generation in layers 8-14 in the anteromedial 
part of the ipsilateral tectum. The observed 
variations in exact site of termination of ipsi- 
lateral retinotectal projections may reflect 
sensitivity of techniques (autoradiography 
vs, degeneration) or species differences in 
the predominance of type of synapse (e.g., 
axodendritic in the cell sparse layer 9 vs. 
axosomatic in layers with greater cell den- 
sity). 
The possibility exists that ipsilateral ret- 
inotectal fibers have been overlooked in other 
studies since they represent a very small 
number to a limited site. We feel that the 
autoradiographic method proved invaluable 
to our demonstration of these fibers, since in 
our anterograde degeneration material dem- 
onstration of such a projection was, at best, 
equivocal. 
Hypothalamus 
Although the presence of a retinohypo- 
thalamic connection has been mentioned in 
other accounts of the reptilian visual system 
we have been able to demonstrate the precise 
location of the terminals of these retino- 
hypothalamic fibers in relation to the cells 
of the supraoptic nucleus. Armstrong (1950) 
and Butler and Northcutt (1971) found no 
evidence of optic fibers terminating in the 
hypothalamus of Lacerta, Iguana, or Anolis. 
Ebbesson (1970) lists the hypothalamus as 
an area which receives contralateral retinal 
afferents, but he does not mention any specific 
hypothalamic nucleus. In more recent papers, 
Butler (1974) and Northcutt and Butler 
(1974a) mention the possibility of fibers pro- 
jecting into the hypothalamus in Xantusia 
and Gekko but did not see terminal areas. 
With the anterograde degeneration tech- 
nique, one often sees fibers within the hypo- 
thalamus which may be undergoing degen- 
eration, but with the autoradiographic label- 
ing of terminals the existence and precise 
location of these fibers can be ascertained. 
Using autoradiography in Caiman sclerops, 
Reperant (1975) also found the supraoptic 
nucleus to be the site of a contralateral 
retinal projection. 
Nucleus of the Basal Optic Tract 
The nucleus of the basal optic tract has 
been identified as a recipient of contralateral 
retinal fibers in all lizard brains studied. This 
structure is also known as the nucleus opticus 
tegmenti (Armstrong, 1950; Butler, 1974; 
Butler and Northcutt, 1971 ; Northcutt 
and Butler, 1974a) or nucleus of the acces- 
sory optic tract (Ebbesson, 1970). 
Conclusions 
By experimental techniques of anterograde 
degeneration and anterograde axonal trans- 
port, used in the present study, the regions 
of termination of retinal ganglion cells can 
be identified (Fig. 6). Such identification is 
the first step in understanding the function 
which these brain nuclei play in the visual 
behavior of the animal. 
ABBREVIATIONS 
ac. Anterior commissure 
AH, Anterior hypothalamic area 
AT, Area triangularis 
AVA, Area ventralis anterior 
AVM, Area ventromedialis 
DA, Dorsal hypothalamic area 
DH, Nucleus dorsalis hypothalami 
